62 files changed, 6783 insertions, 414 deletions

diff --git a/.gitignore b/.gitignore
index a140ec2..f1140f6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,6 @@
 *.pem
 *.key
 /text
+
+# The browser build pins its dependency tree.
+!web/play/package-lock.json
diff --git a/AGENTS.md b/AGENTS.md
index ab794f8..3827957 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -37,20 +37,79 @@
   transaction.
 
 ## Crash
-- The client draws the multiplier from its own clock for display only. A
-  cashout carries a session id and nothing else; the multiplier and payout come
-  from the server's clock at receipt.
+- The client draws the multiplier from its own clock, corrected by the server
+  time in `HELLO`/`PONG`, for display only. A cashout carries a session id and
+  nothing else; the multiplier and payout come from the server's clock at
+  receipt.
 - Never send the crash point to the client before the round ends. A client that
   knows it can cash out at `crash - epsilon` every round for a guaranteed win.
 - The crash point is `max(1.0, (1 - edge) / (1 - u))`; do not "fix" the 1% of
   rounds that crash at 1.00x. That is where the house edge is charged on an
   instant cashout, and it is why no cashout lockout is needed.
+- Each round draws a 32-byte seed. `commit = sha256(seed)` goes out with
+  `CRASH_START`; the seed itself is revealed only when the round ends. The
+  crash point is `crash_point_from_seed(seed)` (first eight bytes, big-endian,
+  over 2^64), so a client can recompute it. Never reveal the seed while the
+  round is live. The guarantee is "fixed before you acted", not "ungrindable";
+  see ADR 0004.
 - The crash event is a server-initiated line (`CRASH_BUSTED`), not a reply.
   Client code must drain the socket on a timer and route pushed lines by
   prefix instead of assuming the next line answers the last request.
 - `ServerCore::poll` must be idempotent: it settles the round, removes the
   session, and pushes once. A second poll must produce nothing.
 
+## Protocol v5
+- Every packet is `[u32 big-endian length][UTF-8 payload]`, at most 64 KiB.
+  Never read a declared length above the limit into memory; close instead.
+- Payloads are `REQ <id> [idem=<token>] <command>`, `RES <id> <body>` and
+  `EVT <seq> <body>`. The command/body text grammar is unchanged.
+- `ClientCore` allocates request ids. Adapters must return a reply with
+  `handle_reply_id`; a reply with an unknown id is ignored, never applied to
+  whatever request happens to be pending.
+- The server caches the last 256 request ids **per connection** and replays a
+  matching reply. A reused id with a different payload is an error. Do not make
+  this durable without a new ADR.
+- `HELLO` and `PONG` carry Unix milliseconds. The offset is for display and
+  interpolation; the server settles crash. Never derive a payout from a
+  browser or gateway clock.
+- While a crash round runs, `poll` pushes at most one `crash.tick` per 100 ms
+  per session. Settlement (`CRASH_BUSTED`) is never dropped or replaced by a
+  tick.
+- A wire change is a MAJOR bump. Do not add a compatibility mode for v4.
+
+## Web gateway (`webd/`)
+- The browser is a frontend, not a client. It sends `Command` JSON and renders
+  `View` JSON. It must never parse the game wire, compute a payout, or hold a
+  credential.
+- `webd/` is a separate workspace member. Its dependencies (tungstenite,
+  serde_json, cookie handling) must not enter the TUI, GUI or server build
+  graph.
+- One session thread owns one `ClientCore` and one upstream TLS connection.
+  No async runtime, no browser TOFU: `ZAGAN_UPSTREAM_FINGERPRINT` is required
+  and a mismatch refuses to connect.
+- The session cookie is HttpOnly, SameSite=Strict, and Secure on HTTPS. Never
+  store a password or credential in the browser or gateway. Session-only auth;
+  no remember-me without a new ADR.
+- Close is not forfeit: the gateway holds upstream for `ZAGAN_GRACE_SECONDS`
+  (default 60). Expiry closes upstream, which is the server's forfeit. A new
+  socket with the same cookie takes over; tell the old tab it was replaced.
+- Bind to loopback and let nginx terminate TLS. Check `Origin` against
+  `ZAGAN_WEB_ORIGIN`. `/ws` is the only gateway route; `/play/` is static.
+- A gateway restart loses live sessions and forfeits their rounds. Do not add
+  protocol-level resume here without an ADR.
+
+## Web app (`web/play/`)
+- Vanilla TypeScript + esbuild. No framework runtime, no game rules, no wire
+  protocol. DOM for the shell, canvas for the game surface.
+- Colours and spacing come from `web/play/style.css`, which mirrors
+  `gui/src/theme.rs`. Felt green is only ever the roulette table.
+- Build with `cd web/play && npm ci && npm run build`; commit the generated
+  `app.js` so the site needs no Node at deploy time.
+- `/play/` is the app; `/` stays the download page. Web v1 is play-money only:
+  no deposits, withdrawals or KYC copy.
+- The browser cookie covers refresh and the grace window only. A closed tab
+  that returns later logs in again.
+
 ## GUI
 - The GUI is a second frontend over `ClientCore`, not a second client.
   Frontends send `Command` and render `View`; the core owns navigation and
diff --git a/CONTEXT.md b/CONTEXT.md
new file mode 100644
index 0000000..6fefd53
--- /dev/null
+++ b/CONTEXT.md
@@ -0,0 +1,76 @@
+# Context
+
+zagan-bet is a small play-money casino: one Rust workspace with a shared
+library, a terminal client, a server, a desktop GUI and a browser frontend. This file names the things the code and the docs talk about. Keep it
+current when a term changes meaning.
+
+## Product terms
+
+- **Play credit** — the unit a player wins and loses. Registration grants a
+  starting balance. There are no deposits, withdrawals, cash-outs or KYC; the
+  web app is a game, not a regulated gambling service.
+- **Server** — the authoritative process. It owns the database, the game
+  rules, the balances, the random draws and the clock used to settle crash.
+- **Frontend** — a presentation adapter over `ClientCore`: the terminal client,
+  the egui desktop app, or the browser app behind the web gateway. Frontends
+  send `Command` values and render `View` values. They never compute payouts.
+- **ClientCore** — the I/O-free state machine shared by every frontend. It owns
+  navigation, the current game view, the pending request, and the local clock
+  anchor for crash. It contains no terminal, network or egui types.
+- **Gateway (`webd`)** — a server-side frontend adapter for the browser. It owns
+  one upstream TLS connection and one `ClientCore` per browser session, and
+  translates browser JSON into `Command`/`View`. The browser never speaks the
+  game wire protocol.
+- **Upstream** — the game server the gateway connects to. Its address and SPKI
+  fingerprint are operator configuration. The browser never sees a certificate.
+- **Session** — one browser login held by the gateway. Identified by an
+  HttpOnly cookie. A refresh or a new tab reattaches to the same session during
+  the grace window; a later visit starts a new login.
+
+## Wire terms
+
+- **Frame** — `[u32 length][UTF-8 payload]`, length big-endian, at most 64 KiB.
+  The frame is the unit of transport; the payload is text.
+- **Envelope** — the first token of a frame payload:
+  - `REQ <id> [idem=<token>] <command>` — client request.
+  - `RES <id> <body>` — the reply to that request.
+  - `EVT <seq> <body>` — a server-initiated event, numbered per connection.
+- **Request id** — a client-chosen `u64`, unique on the connection while its
+  reply is cached. It correlates a reply with the request that caused it.
+- **Idempotency key** — an optional opaque token on a request. The connection
+  caches the last 256 request ids; resending the same id and payload replays the
+  stored reply instead of performing the action twice.
+- **Event sequence** — a server-chosen `u64`, incremented once per `EVT` on a
+  connection. Clients use it to drop duplicates and to notice gaps.
+- **HELLO** — the first request after TLS. Client and server must share
+  `MAJOR.MINOR`; the reply carries the server version, download URL and the
+  server's Unix time in milliseconds.
+- **Tick** — `EVT crash.tick session=<id> t=<server_ms> m=<multiplier>`, pushed
+  at most every 100 ms while a crash round runs. The server clock still settles
+  a cash-out.
+- **Commit** — `sha256(seed)` in hex, sent with `CRASH_START` before the player
+  can act. **Reveal** — the seed itself, sent when the round ends. The crash
+  point is a pure function of the seed, so a player can check both.
+
+## Deployment terms
+
+- **Download site** — `web/`: `index.php` lists builds, `latest.php` feeds the
+  stable installers, `install.sh`/`install.ps1` fetch and verify the newest app.
+- **Play app** — the static browser bundle under `/play/`, built from
+  `web/play/` with esbuild and served by nginx.
+- **Grace window** — the 60 seconds the gateway keeps an upstream connection
+  after the last browser socket closes. Reattaching within it preserves a live
+  round; expiry closes upstream and the server forfeits per its existing rule.
+- **Takeover** — a new browser connection presenting an existing session cookie
+  replaces the old socket; the old tab is told it was replaced.
+
+## Invariants
+
+- One payout formula, one place. `process_action` stores raw data;
+  `calculate_result` derives the result. Frontends only render.
+- Every balance mutation is transactional, and an audit row exists before the
+  balance moves.
+- A crash point never reaches a client before the round ends.
+- The server clock, not a browser or gateway clock, settles cash-out.
+- `MAJOR.MINOR` is lockstep between client and server; only the patch component
+  may differ. A wire change is a MAJOR bump.
diff --git a/Cargo.toml b/Cargo.toml
index 16ed8c6..0a4aa76 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,9 +1,9 @@
 [workspace]
-members = ["gui"]
+members = ["gui", "webd"]
 
 [package]
 name = "zagan-bet"
-version = "4.4.0"
+version = "5.0.0"
 edition = "2024"
 license = "GPL-3.0-or-later"
 
diff --git a/docs/GUI-PLAN.md b/docs/GUI-PLAN.md
index c0370a0..95ec922 100644
--- a/docs/GUI-PLAN.md
+++ b/docs/GUI-PLAN.md
@@ -5,7 +5,10 @@ Decisions and rationale live in `docs/adr/0001-gui-frontend-architecture.md` and
 
 ## Non-goals
 
-Audio, 3D, macOS, auto-update, a browser client, and pixel-golden tests in CI.
+Audio, 3D, macOS, auto-update, a webview inside the desktop app, and
+pixel-golden tests in CI. A separate browser frontend is no longer a non-goal:
+it shipped in v5.0.0 through the `webd/` gateway, planned in
+`docs/WEB-PLAN.md`.
 
 ## Phase 0 — version handshake (v4.0.0)
 
diff --git a/docs/PROTOCOL-IDEAS.md b/docs/PROTOCOL-IDEAS.md
new file mode 100644
index 0000000..3991a84
--- /dev/null
+++ b/docs/PROTOCOL-IDEAS.md
@@ -0,0 +1,170 @@
+# Server ↔ client transport ideas
+
+Status: design notes, written 2026-11-08. Items 1–5 were adopted (with the
+differences recorded in `docs/adr/0004-protocol-v5.md`): correlation ids,
+per-connection idempotency, clock sync + ticks, commit–reveal crash, and
+length-prefixed framing. Items 6–7 remain future work.
+
+These came out of reviewing zagan-bet's transport, but they were prompted by a
+*different* app. Nothing here is a backlog item for this repository. The
+zagan-bet paths are included because that is where the patterns were worked
+out; treat the ideas as portable.
+
+zagan-bet's current shape, for context:
+
+- TLS with TOFU over the certificate's SPKI fingerprint, trust decision after
+  the handshake and before credentials (`src/client/transport.rs`,
+  `src/tofu.rs`).
+- Newline-delimited text lines over the TLS stream (`src/protocol.rs`).
+- `HELLO MAJOR.MINOR` lockstep before auth (`src/version.rs`).
+- Request/reply plus exactly one server-initiated line, `CRASH_BUSTED`
+  (`src/bin/server/handler.rs`, `ServerCore::poll`).
+- `ClientCore` is I/O-free; frontends send `Command` and render `View`
+  (`src/client/core.rs`). The GUI owns the stream in `gui/src/net.rs`.
+
+Each idea below lists the wire shape, where it would attach, and the cost.
+
+## 1. Correlation IDs, so a single `Pending` can go away
+
+One request in flight, and pushes distinguished by string prefix
+(`expects_push`, `CRASH_BUSTED`, `src/client/core.rs:622`). A late reply can
+race a pushed bust; the code already has a special case for it
+(`src/client/core.rs:211`). An envelope removes the whole class:
+
+```
+REQ 42 idem=f3a1... INFO
+RES 42 OK balance=1200 account=...
+EVT seq=913 crash.tick {"session_id":"...","server_ms":837412,"multiplier":1.42}
+```
+
+`REQ`/`RES` correlate by id; `EVT` is connection-scoped and never answers
+anything. The core keeps a map of in-flight requests instead of one `Option`,
+and "a stale reply must not clobber the result" becomes a generic rule rather
+than a crash-specific branch. Also allows pipelining, e.g. clock probes while a
+`HISTORY` is in flight, without app-layer head-of-line stalls. Keep line
+framing for now; just prepend tokens.
+
+## 2. Idempotency keys on every balance mutation
+
+A request can be applied server-side and the reply lost. Today that is safe
+only because nothing retries automatically; the moment a client retries or
+resumes, it can double-debit.
+
+```
+REQ 43 idem=9c2e... PLAY_START crash 50
+```
+
+Server keeps `seen_requests (idem PRIMARY KEY, user, reply, created_at)`. The
+replay check, the debit, and the row insert sit in the same transaction as the
+existing reservation (`database::reserve_play`). A duplicate returns the stored
+reply and never re-executes. TTL-sweep at startup next to
+`recover_orphaned_reservations`. Scope by user, not connection, so a resumed
+session cannot replay someone else's key.
+
+## 3. Clock sync and a real tick stream
+
+zagan-bet advances timed games on read timeouts (`POLL_INTERVAL`,
+`src/bin/server/handler.rs:7`) and the client draws crash locally from an
+`Instant`. Payouts are correctly server-clock authoritative, but the client
+does not know its offset. Two parts:
+
+**Clock sync**, Cristian/NTP style over the existing connection:
+
+```
+REQ 7 idem=... TIME t0=837412
+RES 7 OK t0=837412 t1=837498     # t1 = server monotonic ms
+```
+
+`offset = t1 - (t0 + t2) / 2`; keep the minimum-RTT sample over a sliding
+window. Render timed games from `server_now`.
+
+**Ticks** at 10–20 Hz, monotonic `seq`, no reply semantics:
+
+```
+EVT seq=914 crash.tick {"session_id":"...","server_ms":837520,"multiplier":1.44}
+```
+
+Coalesce in the writer: replace an unqueued tick, never drop a settlement.
+That also enables lag compensation — render at `server_now - presentation_delay`
+(e.g. 150 ms) so the displayed number never exceeds what the server accepts at
+the moment of a click. A cleaner fairness story than trusting the client clock.
+
+## 4. Commit–reveal instead of a hidden `Option<f64>`
+
+zagan-bet already withholds the crash point (`CrashState::crash_point`,
+`src/crash.rs`). Make it verifiable:
+
+```
+RES 51 OK COMMIT 7f3a... 4b9c...   # sha256(server_seed), round id
+...round runs...
+EVT seq=980 crash.busted {"seed":"<server_seed>","crash_point":2.37,...}
+```
+
+Player supplies a client seed; the server echoes it. Crash point derives from
+`HMAC-SHA256(server_seed, client_seed)` → 52 bits → `[0, 1)` → the existing
+`crash_point_from_uniform`. Verification is a pure function and belongs in a
+unit test, not a network test. A hash chain lets the server pre-commit every
+future round at session start; that is stronger than needed in most cases.
+
+## 5. Framing: length prefix, then maybe QUIC
+
+Weaknesses in newline framing:
+
+- `LineBuffer` grows without bound; a client that never sends `\n` is a memory
+  DoS. Reject oversized frames *before* allocating.
+- `from_utf8_lossy` silently rewrites corrupt input. Newline framing is only
+  safe while `serde_json` keeps escaping newlines — an implicit dependency.
+
+```
+[u32 LE len][u8 proto_version][u8 kind][payload]
+```
+
+This allows a move to `postcard`/CBOR later without touching the read loop.
+The larger swing is QUIC (`quinn`): separate streams so a slow `HISTORY`
+cannot block ticks, 0-RTT resumption, connection migration for NAT rebinds
+mid-round, and unreliable datagrams for ticks where latest-wins beats
+retransmission. zagan-bet already uses rustls on the client, so this would also
+drop OpenSSL from the server build. Cost: UDP reachability, TLS 1.3 only, a
+rustls bump.
+
+## 6. Resume tokens and a blocking reader thread
+
+`AUTH` returns an opaque HMAC-signed resume token plus a session id;
+`RESUME <token> since=<seq>` replays missed `EVT`s from a bounded per-session
+buffer. Turns disconnect from "forfeit everything" into a policy choice; a
+server-clocked round is trivially resumable. In zagan-bet this contradicts the
+AGENTS rule that disconnect = forfeit, so it would need an explicit carve-out
+and a grace window.
+
+Separately, both ends poll with timers: the server's 50 ms read timeout, and
+the GUI flipping `SO_RCVTIMEO` to 1 ms every 8 ms in
+`TlsStream::read_available_line`. A dedicated blocking reader thread feeding an
+`mpsc` removes the per-call timeout mutation, `expects_push`, and
+`POLL_INTERVAL`; the handler becomes a `select` over inbound lines, a tick
+deadline, and shutdown. Still no async runtime.
+
+## 7. Small ones worth batching
+
+- `HELLO 5.0 caps=idem,tick,commit` with server-side intersection instead of
+  strict MAJOR.MINOR lockstep for additive changes. Keep MAJOR for framing.
+- Structured errors: `ERR code=INSUFFICIENT_FUNDS retryable=0 msg=...` so the
+  frontend can tell "reconnect" from "show text".
+- `set_nodelay(true)` plus an app-level `PING` deadline; a half-open TCP
+  connection is otherwise noticed only on the next write.
+- Per-connection token-bucket rate limiting. Every inbound line is logged, so a
+  chatty client is also a log-flood/disk problem.
+- A protocol fuzzer (`proptest`/`cargo-fuzz`) asserting the server never panics
+  and `balance >= 0` for arbitrary input, plus transcript-replay tests.
+
+## If only three
+
+1. Correlation IDs + idempotency keys — small, kills two bug classes.
+2. Clock sync + coalesced ticks — turns a special-case push into a generic
+   event channel.
+3. Commit–reveal — cheap, and the strongest fairness story for a betting
+   server.
+
+The envelope plus idempotency is the least invasive pair: it touches
+`src/protocol.rs`, `ServerCore::handle_message`, and
+`ClientCore::handle_reply`, and can sit behind a `caps=` flag so version
+lockstep stays intact.
diff --git a/docs/TESTING.md b/docs/TESTING.md
index 09ceb82..fbd510b 100644
--- a/docs/TESTING.md
+++ b/docs/TESTING.md
@@ -210,9 +210,9 @@ terminal client; a saved login from one signs in the other.
 
 1. `play crash` shows the ready board with a 1.00x multiplier; Space starts and
    reserves the bet.
-2. The multiplier rises smoothly with no network traffic. Cash out with C and
-   confirm the board shows the cashout multiplier, the payout and the new
-   balance.
+2. The multiplier rises smoothly from the server-clock anchor and is refreshed
+   by 10 Hz ticks. Cash out with C and confirm the board shows the cashout
+   multiplier, the payout and the new balance.
 3. On another round, press nothing. The board must switch to `CRASHED at Xx`
    by itself when the crash point is reached, and the bet must be lost.
 4. Press C just as a round crashes. Either it pays or the crashed result wins;
@@ -220,8 +220,11 @@ terminal client; a saved login from one signs in the other.
 5. Q during a live round forfeits the bet; Q when idle just leaves.
 6. Check the audit rows: one per round, `game_type = crash`, the reserved bet,
    the payout, and `crash_point`/`multiplier`/`result` in `details`.
-7. Confirm the crash point is absent from the `CRASH_START` line (it must only
-   appear once the round is over).
+7. Confirm the crash point and seed are absent from the `CRASH_START` message;
+   only `commit` and `started_at` appear. When the round ends, `seed` appears
+   and `sha256(seed) == commit`; recompute the crash point from the seed.
+8. Confirm `CRASH_BUSTED` is an `EVT`, not a `RES`, and that a second poll
+   produces no repeated settlement.
 
 ## Manual restart check
 
@@ -237,7 +240,7 @@ terminal client; a saved login from one signs in the other.
 
 1. Connect a client and server from the same release: the client connects and
    the server log shows the `HELLO` exchange.
-2. Connect a 4.x client to a 3.x server (or the reverse): the client must print
+2. Connect a 5.x client to a 4.x server (or the reverse): the client must print
    `Version mismatch: client ..., server ...` and never reach the login prompt.
 3. With a deliberately skew-built server (PATCH differs) the connection is
    accepted and, when the server's version is newer, the client prints
@@ -269,9 +272,11 @@ terminal client; a saved login from one signs in the other.
 
 ## Packaging checklist
 
-1. Set the version in `Cargo.toml` and `gui/Cargo.toml` (same MAJOR.MINOR),
-   run `cargo test --workspace`, and commit. `publish.sh` refuses a dirty tree
-   because the site links the committed git history as the GPL source.
+1. Set the version in `Cargo.toml`, `gui/Cargo.toml` and `webd/Cargo.toml`
+   (same MAJOR.MINOR), run `cargo test --workspace`, build the browser app
+   (`cd web/play && npm ci && npm run build`), and commit. `publish.sh` refuses
+   a dirty tree because the site links the committed git history as the GPL
+   source.
 2. `./scripts/publish.sh` (add `DEST=` to stage elsewhere). It builds the GUI
    with `gui-release` and the terminal clients and servers. The installers are
    stable site files and are not regenerated.
@@ -284,4 +289,33 @@ terminal client; a saved login from one signs in the other.
    menu entry. It must install the newest version even when an older app sits
    next to it, and refuse a corrupted download.
 5. Repeat on Windows for the `.ps1` installer and the Start-menu shortcut.
+6. Start `webd` against the staging server with a pinned fingerprint and open
+   `/play/` through nginx. Run the manual web checklist below.
+
+## Manual web checklist
+
+1. Open `/play/` in a fresh browser. The auth card must appear; the top bar
+   must not claim a balance until login.
+2. Register, then log in with the password. The lobby must show 1 000 Kr and
+   every game. Refresh the page; the session cookie must reattach and the
+   balance must survive (within `ZAGAN_GRACE_SECONDS`).
+3. Open the same URL in a second tab. The first tab must show "Opened in
+   another tab" and stop reconnecting; the second must continue.
+4. Slots: spin and watch the reels settle on the server result; check the
+   payout and balance. Roulette: place straight, dozen, column and outside
+   chips, right-click one back, clear, spin, and confirm the result.
+5. Blackjack: deal, hit/stand/double, then deal again; forfeiting must warn
+   and lose the reserved bet.
+6. Crash: start a round, watch the curve and ticks, cash out; on another
+   round let it bust. Confirm the reveal line shows `sha256(seed) == commit`
+   and the recomputed crash point matches.
+7. Refresh in the middle of a live crash round. The current view must return
+   with the same `commit` and a rising multiplier; the round must still settle.
+8. Close the tab mid-round and wait past the grace window. The next visit must
+   log in again, and the server must have forfeited the round.
+9. Stop the gateway. The browser must show the reconnect overlay, then recover
+   when `webd` returns. Stop it for longer than the grace window: the round is
+   forfeited and a login is required.
+10. Check the browser console: no credential is stored, the cookie is HttpOnly,
+    and the only network target is `/ws`.
 
diff --git a/docs/WEB-PLAN.md b/docs/WEB-PLAN.md
new file mode 100644
index 0000000..895687b
--- /dev/null
+++ b/docs/WEB-PLAN.md
@@ -0,0 +1,129 @@
+# Browser frontend plan
+
+Status: v1 implemented in 5.0.0. This is the working plan and the deployment
+contract; see `CONTEXT.md` and ADRs 0003/0004 for the decisions.
+
+## Shape
+
+```
+browser ──wss──> nginx ──ws──> webd ──TLS──> game server
+  /play/          /ws          127.0.0.1:8890   127.0.0.1:11525
+  static files    gateway      one thread per    authoritative rules,
+                               browser session  balances, crash clock
+```
+
+- `web/play/` is a static TypeScript app. It sends `Command` JSON and renders
+  `View` JSON. It has no rules and no wire parser.
+- `webd/` is a workspace member. It owns one `ClientCore`, one upstream TLS
+  connection and a 60-second grace window per browser session.
+- `src/protocol.rs` is v5: bounded frames, `REQ`/`RES`/`EVT`, request ids,
+  server time and crash commit–reveal.
+
+## Phases
+
+1. **Protocol v5** — frames, envelope, correlation, replay cache, clock sync,
+   ticks, commit–reveal, TUI/GUI updates. Done in the 5.0.0 change.
+2. **Gateway** — WS accept, cookie session registry, takeover, grace, pinned
+   upstream, `Command`/`View` JSON. Done in the 5.0.0 change.
+3. **Web shell** — login/register, lobby, history, notices, route at `/play/`.
+   Done in the 5.0.0 change.
+4. **Games** — slots, roulette (felt + chips), blackjack, crash (curve +
+   verification). Done in the 5.0.0 change.
+5. **Deployment** — nginx routes, static build, systemd unit, verification in
+   `scripts/deploy.sh`. Done in the 5.0.0 change.
+
+## Browser contract
+
+Browser → gateway:
+
+```json
+{"type":"command","command":{"Login":{"user":"alice","credential":"<sha256 hex>"}}}
+{"type":"command","command":{"Play":{"game":"crash","bet":10}}}
+{"type":"command","command":"Start"}
+{"type":"ping"}
+```
+
+`Command` uses serde's external tagging because several variants carry a
+primitive or a string. Unit variants are bare strings (`"Spin"`, `"Start"`).
+
+Gateway → browser:
+
+```json
+{"type":"hello","version":"5.0.0","grace_seconds":60,"user":"alice","time":1700000000000}
+{"type":"view","view":{"screen":"lobby", "...": "..."}}
+{"type":"notice","text":"Logged in as alice"}
+{"type":"error","text":"Upstream connection failed: ..."}
+{"type":"replaced"}
+{"type":"pong"}
+```
+
+`View` is internally tagged by `screen` (`lobby`, `history`, `slots`,
+`roulette`, `blackjack`, `crash`). The browser renders each screen; it never
+computes a result.
+
+The cookie is `zagan_session`, HttpOnly, SameSite=Strict, Secure on HTTPS. It
+is set on the WebSocket handshake. It covers refresh and the grace window only;
+there is no remember-me.
+
+## Build and run
+
+```sh
+# static app
+cd web/play
+npm ci
+npm run build          # writes app.js; commit it
+
+# gateway
+cargo build -p zagan-bet-webd --release
+ZAGAN_UPSTREAM=127.0.0.1:11525 \
+ZAGAN_UPSTREAM_FINGERPRINT=<64 hex> \
+ZAGAN_WEB_ORIGIN=https://zagan.2137697.xyz \
+ZAGAN_WEB_BIND=127.0.0.1:8890 \
+target/release/zagan-bet-webd
+```
+
+The fingerprint is the same SPKI SHA-256 the desktop client shows:
+
+```sh
+openssl x509 -in cert.pem -pubkey -noout \
+  | openssl pkey -pubin -outform DER \
+  | sha256sum
+```
+
+Test against a staging site with
+`ZAGAN_WEB_ORIGIN=http://127.0.0.1:8899 ZAGAN_WEB_COOKIE_SECURE=0`.
+
+## Security boundaries
+
+- The gateway binds loopback. nginx terminates TLS and is the only public
+  entry. Do not expose `ZAGAN_WEB_BIND` to the internet.
+- The upstream key is pinned; there is no TOFU and no unsafe mode. A mismatch
+  logs both fingerprints and refuses credentials.
+- The browser has no certificate UI and no credential storage. XSS cannot read
+  the HttpOnly cookie; the backend still must escape every notice.
+- The browser speaks JSON, not the game wire. A malicious page cannot use the
+  gateway as a protocol proxy: `Origin` is checked and the session cookie is
+  SameSite=Strict.
+- The web app is play-money only. No deposits, withdrawals, KYC or real-money
+  claims belong in v1 copy.
+
+## Failure behaviour
+
+| Event | Result |
+| --- | --- |
+| Refresh / new tab, within grace | Same `ClientCore`, current `View` restored |
+| New tab, same cookie | Old tab gets `replaced` and closes; new tab continues |
+| Socket closed, grace expires | Upstream closes; server forfeits live hand |
+| Gateway restart | Sessions lost; players log in again |
+| Upstream disconnect | Browser gets an error, core resets, reconnect attempts |
+| Browser retry of a request | Gateway does not retry; request ids are per connection |
+
+## Verification
+
+- `cargo test --workspace` covers frames, envelope parsing, idempotent replay,
+  commit verification, ticks, core routing and session JSON.
+- `web/play`: `npm run typecheck` and `npm run build`.
+- Manual WS smoke test: connect, login, play slots/crash, refresh in a live
+  crash round, verify the revealed seed.
+- `scripts/deploy.sh` checks `/play/`, `app.js`, `style.css` and the existing
+  download feed.
diff --git a/docs/adr/0001-gui-frontend-architecture.md b/docs/adr/0001-gui-frontend-architecture.md
index 44dca32..e4dd5ac 100644
--- a/docs/adr/0001-gui-frontend-architecture.md
+++ b/docs/adr/0001-gui-frontend-architecture.md
@@ -1,6 +1,7 @@
 # 0001 — GUI is a second frontend over a shared core
 
-Status: accepted, 2026-11-01
+Status: accepted, 2026-11-01; the "no browser" constraint is superseded by
+[0003](0003-web-gateway.md), which adds a browser frontend through a gateway.
 
 ## Context
 
diff --git a/docs/adr/0003-web-gateway.md b/docs/adr/0003-web-gateway.md
new file mode 100644
index 0000000..5337e2b
--- /dev/null
+++ b/docs/adr/0003-web-gateway.md
@@ -0,0 +1,85 @@
+# 0003 — Browser frontend through a server-side gateway
+
+Status: accepted, 2026-11-08
+
+## Context
+
+The game already runs over TLS/TCP with a newline-delimited text protocol. A
+browser cannot open a TCP socket, and putting game rules into JavaScript would
+create a second implementation of payout, session and forfeit logic — exactly
+what the project forbids.
+
+The site must stay a website in the ordinary sense: open `zagan.bet`, log in,
+play. Nothing to install. Balances are play credits; there are no deposits,
+withdrawals or KYC in this decision.
+
+## Decision
+
+1. **The browser is a third frontend over `ClientCore`.** It sends `Command`
+   JSON and renders `View` JSON. It contains no rules, no wire-protocol parser
+   and no balance arithmetic.
+2. **A Rust gateway, `webd/`, owns each session.** One blocking thread per
+   browser session, one `ClientCore`, and one ordinary client TLS connection
+   upstream. The existing `client::transport` and `ClientCore` are reused. No
+   async runtime and no new concurrency style.
+3. **`webd/` is a separate workspace member.** Like `gui/`, its dependencies
+   (tungstenite, HTTP cookie handling) must never enter the TUI, GUI or server
+   build graph.
+4. **Everything is same-origin and operator-configured.** nginx terminates
+   TLS, serves the static app at `/play/`, and proxies `/ws` to the gateway on
+   loopback. The browser never sees a certificate, there is no CORS, and the
+   upstream address (`ZAGAN_UPSTREAM`, default `127.0.0.1:11525`) and SPKI
+   fingerprint (`ZAGAN_UPSTREAM_FINGERPRINT`, required) are gateway config.
+   A mismatch refuses to connect and logs both fingerprints. There is no TOFU
+   and no unsafe mode for the upstream leg.
+5. **Session-only authentication.** Log in per visit. The gateway issues a
+   random HttpOnly, SameSite=Strict, Secure session cookie; the cookie covers a
+   refresh and the grace window only. No credential is stored in the browser or
+   in the gateway. A new connection with the same cookie takes over the session
+   and the old socket is told it was replaced.
+6. **60-second grace window.** When the last browser socket for a session
+   closes, the session thread keeps the upstream connection and `ClientCore`
+   alive for 60 seconds (configurable). A reconnecting socket with the same
+   cookie reattaches and immediately receives the current `View`. Expiry closes
+   upstream, and the server forfeits a live hand per the existing disconnect
+   rule. There is no wire-level resume: the gateway, not the browser, holds the
+   TCP connection.
+7. **Vanilla TypeScript + esbuild.** DOM for login, lobby, history and notices;
+   one canvas for the game surface. No framework runtime. Theme tokens are
+   reused from the desktop palette; felt green is reserved for roulette.
+8. **Web v1 has full parity after trust.** Register, log in, lobby, all four
+   games, history, log out, notices, refresh grace. The connect/trust screens
+   do not exist in the browser because the gateway owns the upstream key.
+
+## Consequences
+
+- One implementation of the rules and parsers remains authoritative, and the
+  TUI/GUI/gateway all exercise the same `ClientCore` tests.
+- The gateway becomes an operational component: it needs a service unit,
+  deployment, logging, a required upstream fingerprint, and a restart story.
+  A gateway restart loses live sessions and therefore forfeits their rounds;
+  this is accepted for v1.
+- The browser cannot recover from a gateway crash by itself. The player logs in
+  again.
+- A 60-second grace window means a live round can outlive a refresh, but not a
+  closed laptop for a minute and a half.
+- WebSocket frames are same-origin JSON, so the page cannot be used as an open
+  proxy by another origin. The gateway also checks the `Origin` header against
+  `ZAGAN_WEB_ORIGIN`.
+- The web app is play-money only. Adding payments later would be a separate
+  product and compliance decision, not a UI change.
+
+## Alternatives considered
+
+- **WASM `ClientCore` in the browser, dumb relay**: reuses Rust in the page,
+  but needs transport, TOFU and credential shims in wasm and a multi-megabyte
+  download for every player. Rejected.
+- **JavaScript rewrite speaking the game protocol**: fastest UI iteration, but
+  a second implementation of rules and payout invariants. Rejected.
+- **Tokio/axum gateway**: idiomatic WebSocket server, but a large async tree
+  and a second concurrency style for one blocking, low-traffic product.
+  Rejected.
+- **Long-lived remember-me in the gateway**: better return visits, but a new
+  credential store and revocation flow. Deferred; session-only first.
+- **Protocol-level resume tokens**: survives a gateway restart, but is a wire
+  change and more state on the server. Deferred.
diff --git a/docs/adr/0004-protocol-v5.md b/docs/adr/0004-protocol-v5.md
new file mode 100644
index 0000000..c74ad83
--- /dev/null
+++ b/docs/adr/0004-protocol-v5.md
@@ -0,0 +1,119 @@
+# 0004 — Protocol v5: frames, envelopes, time and commit–reveal
+
+Status: accepted, 2026-11-08
+
+## Context
+
+The current wire is newline-delimited text over TLS. It has served the TUI and
+GUI well, but four problems are now worth fixing before a browser gateway is
+built on top:
+
+- `LineBuffer` grows without bound if a peer never sends a newline, and there
+  is no explicit maximum message size.
+- A reply is assumed to answer the request that is currently pending. A late
+  reply, a retry or a second in-flight request can clobber state.
+- There is no idempotency: a gateway retry after a timeout can charge a bet
+  twice.
+- The crash multiplier is anchored to each frontend's local clock, and the
+  crash point is only "trust the server".
+
+The web gateway makes the first three worse (it retries and multiplexes) and
+the browser makes the fourth visible (a page and the desktop can disagree).
+
+## Decision
+
+This is one wire change and one `MAJOR` release (`5.0.0`); there is no
+compatibility mode.
+
+### Framing
+
+- Every packet is `[u32 length][payload]`, length big-endian.
+- `payload` is UTF-8 text, at most 64 KiB. A larger declared length is a
+  protocol error and the connection closes; buffers never grow past one frame.
+- The payload has no trailing newline.
+
+### Envelope
+
+- `REQ <id> [idem=<token>] <command>` — client request. `<id>` is a `u64`
+  chosen by the client, monotonically increasing on the connection.
+- `RES <id> <body>` — the reply to that request.
+- `EVT <seq> <body>` — a server-initiated event. `<seq>` is a `u64`,
+  incremented once per event on the connection.
+
+The existing text grammar is the `<command>` and `<body>`; `HELLO 5.0.0`,
+`PLAY_START crash 50`, `GAME_RESULT ...` keep their meaning.
+
+`HELLO` is the first framed request. The server ignores every other command
+before a successful handshake. The reply is
+`HELLO <version> latest=<v> url=<url> time=<unix_ms>`.
+
+### Correlation and idempotency
+
+- The client keeps a request id until its `RES` arrives. Replies are routed by
+  id, never by "the next line".
+- The server keeps a bounded 256-entry FIFO of `(id, payload, reply)` on each
+  connection. A repeated id with the same payload returns the stored reply
+  without executing the command again. A repeated id with a different payload
+  returns `ERROR Request id reused with a different command`.
+- The cache is per connection and in memory. A reconnect is a new game session
+  by design; durable idempotency is deferred.
+- `idem=<token>` is optional metadata for logs and for a future cross-
+  connection cache. The request id is the cache key.
+
+### Clock and ticks
+
+- `HELLO` and `PONG` carry the server's Unix time in milliseconds. `PING`
+  replies `PONG <unix_ms>`.
+- Clients keep an offset between server time and their own clock. The offset is
+  for display and interpolation only; the server clock settles a cash-out.
+- A crash start carries `started_at=<unix_ms>` and `commit=<hex>`.
+- While a crash round runs, the server pushes at most one
+  `EVT <seq> crash.tick session=<id> t=<unix_ms> m=<multiplier>` per 100 ms.
+  The client interpolates between ticks and may keep rendering locally.
+- `CRASH_BUSTED` remains an event, now with the reveal attached.
+
+### Commit–reveal crash
+
+- At round start the server draws 32 random bytes as the round seed and sends
+  `commit = sha256(seed)` in hex. It also sends the crash point's start time.
+- The crash point is a pure function of the seed:
+  `u = u64_be(seed[0..8]) / 2^64`, then
+  `crash_point_from_uniform(u)`. The seed never reaches the client before the
+  round ends.
+- When the round ends (`CRASH_STATE` after cash-out, or `CRASH_BUSTED`), the
+  server includes `seed=<hex>`. A client verifies `sha256(seed) == commit` and
+  recomputes the crash point. The UI can show "verified".
+- This proves the crash point was fixed before the player acted. It does not
+  prove the seed was not ground to a favourable value; a hash chain with client
+  entropy is the documented next step if that matters.
+
+## Consequences
+
+- The TUI, GUI, server and gateway all move to v5 together; a v4 peer is
+  refused at `HELLO`.
+- `LineBuffer` is replaced by a bounded `FrameBuffer`. Existing newline-based
+  tests and helpers are rewritten around frames.
+- `ClientCore` allocates request ids and routes replies by id. Its `Effect`
+  carries the id, so an adapter writes the envelope and hands the `RES` back
+  with the same id.
+- Crash rendering can be smoother and consistent across frontends, and the
+  crash result is independently checkable from the revealed seed.
+- The per-connection cache is deliberately small and forgets on reconnect; a
+  retry after a reconnect is a new action, not a replay.
+
+## Alternatives considered
+
+- **JSON or binary frames**: cleaner types or smaller payloads, but a rewrite
+  of every parser for no scale need. Text inside a bounded frame keeps logs
+  readable and the change small.
+- **Newline-delimited frames with a maximum line length**: still needs a
+  separate envelope and does not bound the buffer as cleanly; a declared length
+  is simpler.
+- **Durable idempotency keyed by `(user, idem)`**: survives reconnects, but the
+  gateway owns retries on one connection and a reconnect is a fresh session.
+  Deferred.
+- **Server seed plus client seed without a commit round-trip**: the server
+  sees the client seed before committing and can bias the pair; a half-measure
+  is worse than an honest per-round commitment.
+- **Hash-chain epoch**: stronger anti-grinding, but requires persistent chain
+  state and a restart story. Deferred.
diff --git a/gui/Cargo.toml b/gui/Cargo.toml
index e216309..8dc09df 100644
--- a/gui/Cargo.toml
+++ b/gui/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "zagan-bet-gui"
-version = "4.4.0"
+version = "5.0.0"
 edition = "2024"
 license = "GPL-3.0-or-later"
 description = "Desktop frontend for zagan-bet"
diff --git a/gui/src/app.rs b/gui/src/app.rs
index af64e5e..df8fec3 100644
--- a/gui/src/app.rs
+++ b/gui/src/app.rs
@@ -16,6 +16,7 @@ use zagan_bet::client::database;
 use zagan_bet::client::paths;
 use zagan_bet::client::view::{Command, LobbyView, View};
 use zagan_bet::history::PlayRecord;
+use zagan_bet::protocol::Packet;
 use zagan_bet::version::{VERSION, is_newer};
 
 use crate::net::{Command as NetCommand, Connected, Event, Failure, Network};
@@ -280,8 +281,8 @@ impl ZaganApp {
                         }
                     }
                 }
-                Effect::SendLine(line) => {
-                    self.net.send(NetCommand::Send(line));
+                Effect::SendRequest { id, payload } => {
+                    self.net.send(NetCommand::Send { id, payload });
                     self.awaiting = Some(Instant::now());
                 }
                 Effect::Disconnect => {
@@ -355,17 +356,18 @@ impl ZaganApp {
                     failure,
                     message,
                 } => self.failed(addr, failure, message),
-                Event::Line(line) => {
-                    if self.core.is_async(&line) {
-                        if let Some(effects) = self.core.handle_async_line(&line) {
+                Event::Packet(packet) => match packet {
+                    Packet::Event { body, .. } => {
+                        if let Some(effects) = self.core.handle_async_line(&body) {
                             self.apply(ctx, effects);
                         }
-                    } else {
+                    }
+                    Packet::Reply { id, body } => {
                         self.awaiting = None;
-                        let effects = self.core.handle_reply(&line);
+                        let effects = self.core.handle_reply_id(id, &body);
                         self.apply(ctx, effects);
                     }
-                }
+                },
                 Event::Closed => {
                     self.session = None;
                     self.awaiting = None;
@@ -384,6 +386,7 @@ impl ZaganApp {
         self.core
             .set_host_info(Some(connected.addr.clone()), connected.fingerprint.clone());
         self.core.set_logged_in(connected.user.clone());
+        self.core.set_server_time(connected.server_time);
         self.login.error = connected.auth_error.clone();
         self.login.user = connected.user.clone().unwrap_or_default();
 
diff --git a/gui/src/net.rs b/gui/src/net.rs
index 7cba604..7882cd3 100644
--- a/gui/src/net.rs
+++ b/gui/src/net.rs
@@ -14,6 +14,7 @@ use eframe::egui;
 use rusqlite::Connection;
 use zagan_bet::client::transport::{self, TlsStream, TransportError, TrustPrompt};
 use zagan_bet::client::{database, paths};
+use zagan_bet::protocol::Packet;
 
 /// How often the worker checks the socket for pushes when idle.
 const POLL: Duration = Duration::from_millis(8);
@@ -24,7 +25,7 @@ const TRUST_TIMEOUT: Duration = Duration::from_secs(120);
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Command {
     Connect { addr: String },
-    Send(String),
+    Send { id: u64, payload: String },
     Disconnect,
     Stop,
 }
@@ -49,6 +50,7 @@ pub struct Connected {
     pub latest: String,
     pub url: String,
     pub elapsed_ms: f32,
+    pub server_time: u64,
 }
 
 /// What the worker tells the UI.
@@ -65,7 +67,7 @@ pub enum Event {
         failure: Failure,
         message: String,
     },
-    Line(String),
+    Packet(Packet),
     Closed,
 }
 
@@ -164,6 +166,7 @@ fn worker(
                             latest: connected.latest,
                             url: connected.url,
                             elapsed_ms: connected.elapsed.as_secs_f64() as f32 * 1000.0,
+                            server_time: connected.server_time,
                         }));
                         stream = Some(connected.stream);
                     }
@@ -177,9 +180,9 @@ fn worker(
                 }
                 ctx.request_repaint();
             }
-            Ok(Command::Send(line)) => {
+            Ok(Command::Send { id, payload }) => {
                 if let Some(open) = &mut stream {
-                    if open.write_line(&line).is_err() {
+                    if open.write_request(id, None, &payload).is_err() {
                         stream = None;
                         let _ = events.send(Event::Closed);
                     }
@@ -198,9 +201,9 @@ fn worker(
         // Drain pushes and replies without blocking the command channel.
         if let Some(open) = &mut stream {
             loop {
-                match open.read_available_line() {
-                    Ok(Some(line)) => {
-                        if events.send(Event::Line(line)).is_err() {
+                match open.read_available_packet() {
+                    Ok(Some(packet)) => {
+                        if events.send(Event::Packet(packet)).is_err() {
                             return;
                         }
                     }
diff --git a/scripts/deploy.sh b/scripts/deploy.sh
index 63bd31c..0527505 100755
--- a/scripts/deploy.sh
+++ b/scripts/deploy.sh
@@ -67,6 +67,7 @@ if [ "$VERIFY_ONLY" -eq 0 ]; then
   RSYNC_FLAGS=(
     -a --delay-updates --human-readable --chmod=D755,F644
     --exclude=README.md --exclude=.gitignore
+    --exclude=play/node_modules
   )
 
   if [[ "$TARGET" == *:* ]]; then
@@ -160,6 +161,16 @@ for local in "${artifacts[@]}"; do
   verified=$((verified + 1))
 done
 
+curl -fsSL --max-time 30 "$origin/play/" -o "$tmp/play.html" \
+  || die "could not fetch the browser app at /play/"
+grep -q 'app.js' "$tmp/play.html" || die "/play/ does not reference app.js"
+for asset in app.js style.css; do
+  curl -fsSL --max-time 30 "$origin/play/$asset" -o "$tmp/$asset" \
+    || die "could not fetch /play/$asset"
+  cmp -s "web/play/$asset" "$tmp/$asset" \
+    || die "/play/$asset served from the site differs from the local file"
+done
+
 [ "$failed" -eq 0 ] || die "verification failed"
 
-echo "==> $verified artifact(s) verified at $URL"
+echo "==> $verified artifact(s) and the browser app verified at $URL"
diff --git a/src/bin/client/connection.rs b/src/bin/client/connection.rs
index f88f62b..e808d90 100644
--- a/src/bin/client/connection.rs
+++ b/src/bin/client/connection.rs
@@ -8,7 +8,7 @@ use parking_lot::Mutex;
 use std::error::Error;
 use zagan_bet::client::transport::{self, TrustPrompt};
 use zagan_bet::client::ui::first_contact_lines;
-use zagan_bet::version::{is_newer, VERSION};
+use zagan_bet::version::{VERSION, is_newer};
 
 pub use zagan_bet::client::transport::TlsStream;
 
@@ -21,7 +21,7 @@ pub fn set_unsafe_mode(unsafe_mode: bool) {
 pub fn connect(
     addr: &str,
     conn: &rusqlite::Connection,
-) -> Result<(TlsStream, Option<String>), Box<dyn Error>> {
+) -> Result<(TlsStream, Option<String>, u64), Box<dyn Error>> {
     let unsafe_mode = *UNSAFE_MODE.lock();
 
     // The terminal has no dialog: print the first-contact notice and trust.
@@ -53,5 +53,5 @@ pub fn connect(
         println!("Authentication failed: {error}");
     }
 
-    Ok((connected.stream, connected.user))
+    Ok((connected.stream, connected.user, connected.server_time))
 }
diff --git a/src/bin/client/repl.rs b/src/bin/client/repl.rs
index cfdcdd5..deb5743 100644
--- a/src/bin/client/repl.rs
+++ b/src/bin/client/repl.rs
@@ -14,15 +14,15 @@ use crossterm::{
 use sha2::{Digest, Sha256};
 
 use zagan_bet::client::core::{ClientCore, Effect};
-use zagan_bet::client::input::{game_input, Editor, GameInput, Input, Key};
-use zagan_bet::client::shell::{self, Shell};
-use zagan_bet::client::view::{RoulettePhase, View};
 use zagan_bet::client::database;
+use zagan_bet::client::input::{Editor, GameInput, Input, Key, game_input};
+use zagan_bet::client::shell::{self, Shell};
 use zagan_bet::client::ui::{
-    display_width, format_pong, help_lines, host_lines, input_cursor_column,
-    lines_to_move_up, terminal_size_warning, visual_line_count, MIN_COLUMNS, MIN_ROWS,
+    MIN_COLUMNS, MIN_ROWS, display_width, format_pong, help_lines, host_lines, input_cursor_column,
+    lines_to_move_up, terminal_size_warning, visual_line_count,
 };
-use zagan_bet::protocol::io_failure_message;
+use zagan_bet::client::view::{RoulettePhase, View};
+use zagan_bet::protocol::{Packet, io_failure_message};
 use zagan_bet::roulette::{WHEEL, color as roulette_color};
 
 use crate::connection::TlsStream;
@@ -78,9 +78,10 @@ impl ClientState {
     pub fn connect_to(&mut self, addr: &str) {
         self.addr = Some(addr.to_string());
         match crate::connection::connect(addr, &self.conn) {
-            Ok((stream, authed_user)) => {
+            Ok((stream, authed_user, server_time)) => {
                 self.stream = Some(stream);
                 self.core.set_connected(true);
+                self.core.set_server_time(server_time);
                 self.core.set_logged_in(authed_user);
                 let fingerprint = database::get_fingerprint(&self.conn, addr);
                 self.core.set_host_info(Some(addr.to_string()), fingerprint);
@@ -126,9 +127,7 @@ impl ClientState {
                                         key,
                                     ) {
                                         GameInput::Quit => vec![Effect::Quit],
-                                        GameInput::Command(command) => {
-                                            self.core.command(command)
-                                        }
+                                        GameInput::Command(command) => self.core.command(command),
                                         GameInput::None => Vec::new(),
                                     }
                                 } else {
@@ -189,10 +188,10 @@ impl ClientState {
             let Some(mut stream) = self.stream.take() else {
                 return false;
             };
-            let line = match stream.read_available_line() {
-                Ok(line) => {
+            let packet = match stream.read_available_packet() {
+                Ok(packet) => {
                     self.stream = Some(stream);
-                    line
+                    packet
                 }
                 Err(_) => {
                     self.core.set_connected(false);
@@ -201,13 +200,15 @@ impl ClientState {
                 }
             };
 
-            let Some(line) = line else {
+            let Some(packet) = packet else {
                 return false;
             };
 
-            let effects = match self.core.handle_async_line(&line) {
-                Some(effects) => effects,
-                None => self.core.handle_reply(&line),
+            let effects = match packet {
+                Packet::Event { body, .. } => {
+                    self.core.handle_async_line(&body).unwrap_or_default()
+                }
+                Packet::Reply { id, body } => self.core.handle_reply_id(id, &body),
             };
             if self.apply_effects(effects) {
                 return true;
@@ -259,13 +260,13 @@ impl ClientState {
                     self.draw_region(&lines);
                 }
                 Effect::ClearRegion => self.clear_region(),
-                Effect::SendLine(line) => {
-                    let is_ping = line == "PING";
+                Effect::SendRequest { id, payload } => {
+                    let is_ping = payload == "PING";
                     let started = Instant::now();
-                    let reply = self.send_and_read(&line);
+                    let reply = self.send_and_read(id, &payload);
                     let elapsed = started.elapsed();
-                    let mut more = self.core.handle_reply(&reply);
-                    if is_ping && reply.trim() == "PONG" {
+                    let mut more = self.core.handle_reply_id(id, &reply);
+                    if is_ping && reply.trim().starts_with("PONG") {
                         for effect in &mut more {
                             if let Effect::Print(lines) = effect {
                                 for text in lines {
@@ -488,31 +489,30 @@ impl ClientState {
         self.prompt_text = text.to_string();
     }
 
-    fn send_and_read(&mut self, line: &str) -> String {
+    fn send_and_read(&mut self, id: u64, line: &str) -> String {
         let Some(mut stream) = self.stream.take() else {
             return "ERROR Not connected".to_string();
         };
 
         // A crash event can be pushed while a request is in flight. Route those
-        // lines as they arrive and keep waiting for the actual reply.
+        // events as they arrive and keep waiting for the reply with this id.
         let mut pushed: Vec<String> = Vec::new();
         let result = (|| -> std::io::Result<String> {
-            stream.write_line(line)?;
+            stream.write_request(id, None, line)?;
             loop {
-                let mut response = String::new();
-                let read = stream.read_line(&mut response)?;
-                if read == 0 {
-                    return Err(std::io::Error::new(
-                        std::io::ErrorKind::UnexpectedEof,
-                        "connection closed",
-                    ));
-                }
-                let response = response.trim_end().to_string();
-                if self.core.is_async(&response) {
-                    pushed.push(response);
-                    continue;
+                match stream.read_packet()? {
+                    None => {
+                        return Err(std::io::Error::new(
+                            std::io::ErrorKind::UnexpectedEof,
+                            "connection closed",
+                        ));
+                    }
+                    Some(Packet::Event { body, .. }) => pushed.push(body),
+                    Some(Packet::Reply { id: reply_id, body }) if reply_id == id => {
+                        return Ok(body);
+                    }
+                    Some(Packet::Reply { .. }) => continue,
                 }
-                return Ok(response);
             }
         })();
 
@@ -614,7 +614,11 @@ impl ClientState {
                 short_fingerprint(&identity),
                 host
             ),
-            Ok(false) => println!("No saved login for server {} ({}).", short_fingerprint(&identity), host),
+            Ok(false) => println!(
+                "No saved login for server {} ({}).",
+                short_fingerprint(&identity),
+                host
+            ),
             Err(error) => println!("Failed to forget the saved login: {}", error),
         }
     }
@@ -625,10 +629,9 @@ impl ClientState {
             return;
         };
         match database::forget_host(&self.conn, &target) {
-            Ok(outcome) if outcome.credentials_removed => println!(
-                "Cleared trust and stored credentials for {}.",
-                target
-            ),
+            Ok(outcome) if outcome.credentials_removed => {
+                println!("Cleared trust and stored credentials for {}.", target)
+            }
             Ok(outcome) => {
                 println!("Cleared trust for {}.", target);
                 if !outcome.siblings.is_empty() {
@@ -665,7 +668,8 @@ impl ClientState {
 
             let hashed = format!("{:x}", Sha256::digest(password.as_bytes()));
             let message = format!("AUTH {} {}", username, hashed);
-            let response = self.send_and_read(&message);
+            let id = self.core.allocate_request_id();
+            let response = self.send_and_read(id, &message);
             let response = response.trim();
 
             if response.starts_with("OK") {
@@ -709,7 +713,8 @@ impl ClientState {
 
         let hashed = format!("{:x}", Sha256::digest(password.as_bytes()));
         let message = format!("REGISTER {} {}", username, hashed);
-        let response = self.send_and_read(&message);
+        let id = self.core.allocate_request_id();
+        let response = self.send_and_read(id, &message);
         let response = response.trim();
 
         if response == format!("REGISTERED {}", username) {
diff --git a/src/bin/server/handler.rs b/src/bin/server/handler.rs
index dffae69..e6b623f 100644
--- a/src/bin/server/handler.rs
+++ b/src/bin/server/handler.rs
@@ -1,6 +1,7 @@
 use std::time::Duration;
 
 use crate::tls::TlsStream;
+use zagan_bet::protocol::{event_line, parse_request, reply_line};
 use zagan_bet::server::core::{ConnectionState, ServerCore};
 
 /// How long the connection waits for a request before advancing timed games.
@@ -30,24 +31,35 @@ pub fn handle_client_tls(mut stream: TlsStream) {
     }
 
     let mut state = ConnectionState::default();
+    let mut event_seq = 0u64;
     println!("[TLS Client connected] {client_addr}");
 
     'connection: loop {
-        let mut line = String::new();
-        match stream.read_line(&mut line) {
+        let mut frame = String::new();
+        match stream.read_frame(&mut frame) {
             Ok(0) => break,
             Ok(_) => {
-                let line = line.trim();
-                if !line.is_empty() {
-                    let user = state.user().unwrap_or("guest").to_string();
-                    println!("[{user} @ {client_addr}] Received: {line}");
-                    let response = core.handle_message(&mut state, line);
-                    if let Err(error) = stream.write_line(&response) {
-                        eprintln!("Write error: {error}");
-                        break;
+                let user = state.user().unwrap_or("guest").to_string();
+                println!("[{user} @ {client_addr}] Received: {frame}");
+                match parse_request(&frame) {
+                    Ok(request) => {
+                        let response = core.handle_request(&mut state, &request);
+                        let reply = reply_line(request.id, &response);
+                        if let Err(error) = stream.write_frame(&reply) {
+                            eprintln!("Write error: {error}");
+                            break;
+                        }
+                        let user = state.user().unwrap_or("guest");
+                        println!("[{user} @ {client_addr}] Sent: {reply}");
+                    }
+                    Err(message) => {
+                        let reply = reply_line(0, &format!("ERROR {message}"));
+                        if let Err(error) = stream.write_frame(&reply) {
+                            eprintln!("Write error: {error}");
+                            break;
+                        }
+                        eprintln!("Malformed request from {client_addr}: {reply}");
                     }
-                    let user = state.user().unwrap_or("guest");
-                    println!("[{user} @ {client_addr}] Sent: {response}");
                 }
             }
             Err(error)
@@ -65,12 +77,17 @@ pub fn handle_client_tls(mut stream: TlsStream) {
         }
 
         for push in core.poll(&state) {
-            if let Err(error) = stream.write_line(&push) {
+            event_seq = event_seq.wrapping_add(1);
+            let event = event_line(event_seq, &push);
+            if let Err(error) = stream.write_frame(&event) {
                 eprintln!("Write error: {error}");
                 break 'connection;
             }
-            let user = state.user().unwrap_or("guest");
-            println!("[{user} @ {client_addr}] Pushed: {push}");
+            // Ticks are 10 Hz per live round; logging them floods the disk.
+            if !push.starts_with("crash.tick ") {
+                let user = state.user().unwrap_or("guest");
+                println!("[{user} @ {client_addr}] Pushed: {event}");
+            }
         }
     }
 
diff --git a/src/bin/server/tls.rs b/src/bin/server/tls.rs
index 420b5b4..eb94637 100644
--- a/src/bin/server/tls.rs
+++ b/src/bin/server/tls.rs
@@ -1,7 +1,7 @@
 use std::io::{Read, Write};
 use std::net::TcpStream;
 
-use zagan_bet::protocol::LineBuffer;
+use zagan_bet::protocol::{FrameBuffer, write_frame};
 
 #[derive(Clone)]
 pub struct TlsServer {
@@ -44,34 +44,31 @@ impl TlsServer {
 
 pub struct TlsStream {
     stream: native_tls::TlsStream<TcpStream>,
-    lines: LineBuffer,
+    frames: FrameBuffer,
 }
 
 impl TlsStream {
     pub fn new(stream: native_tls::TlsStream<TcpStream>) -> Self {
         Self {
             stream,
-            lines: LineBuffer::new(),
+            frames: FrameBuffer::new(),
         }
     }
 
-    pub fn read_line(&mut self, s: &mut String) -> std::io::Result<usize> {
-        match self.lines.read_line(&mut self.stream)? {
-            Some(line) => {
-                s.push_str(&line);
-                s.push('\n');
-                Ok(line.len() + 1)
+    /// Read one protocol frame. `Ok(0)` is EOF with no partial frame.
+    pub fn read_frame(&mut self, out: &mut String) -> std::io::Result<usize> {
+        match self.frames.read_frame(&mut self.stream)? {
+            Some(frame) => {
+                let length = frame.len();
+                out.push_str(&frame);
+                Ok(length)
             }
             None => Ok(0),
         }
     }
 
-    pub fn write_line(&mut self, msg: &str) -> std::io::Result<()> {
-        use std::io::Write;
-        self.stream.write_all(msg.as_bytes())?;
-        self.stream.write_all(b"\n")?;
-        self.stream.flush()?;
-        Ok(())
+    pub fn write_frame(&mut self, msg: &str) -> std::io::Result<()> {
+        write_frame(&mut self.stream, msg)
     }
 
     pub fn peer_addr(&self) -> std::io::Result<std::net::SocketAddr> {
diff --git a/src/client/core.rs b/src/client/core.rs
index 6d8294c..278dc00 100644
--- a/src/client/core.rs
+++ b/src/client/core.rs
@@ -3,17 +3,16 @@ use crate::client::games::response::{
     parse_blackjack_response, parse_crash_response, parse_history_response,
     parse_roulette_response, parse_spin_response,
 };
+use crate::client::ui::{game_lines, history_lines};
 use crate::client::view::{
     BlackjackView, Command, CrashView, HistoryView, LobbyView, RouletteView, SlotsView, View,
 };
-use crate::client::ui::{game_lines, history_lines};
 use crate::crash::{CrashState, multiplier_at};
-use crate::history::{PlayRecord, MAX_HISTORY};
+use crate::history::{MAX_HISTORY, PlayRecord};
 use crate::roulette::{BetTarget, Bets};
+use crate::version::{parse_pong, unix_time_ms};
 use std::time::{Duration, Instant};
 
-
-
 /// High-level actions produced by the client core. The terminal adapter is
 /// responsible for turning these into crossterm calls and network writes.
 #[derive(Debug, Clone, PartialEq)]
@@ -24,8 +23,8 @@ pub enum Effect {
     Render(View),
     /// Remove the game board region.
     ClearRegion,
-    /// Send one protocol line and feed the reply to `handle_reply`.
-    SendLine(String),
+    /// Send one enveloped request and route its reply back by `id`.
+    SendRequest { id: u64, payload: String },
     /// Drop the connection.
     Disconnect,
     /// Leave the program.
@@ -61,6 +60,10 @@ pub struct ClientCore {
     connected: bool,
     logged_in: Option<String>,
     pending: Option<Pending>,
+    /// Id of the request whose reply fills `pending`.
+    pending_id: Option<u64>,
+    /// Next correlation id allocated on this connection.
+    next_request_id: u64,
     balance: Option<i64>,
     /// Account number from the last `INFO`, shown by both frontends.
     account: Option<String>,
@@ -68,6 +71,13 @@ pub struct ClientCore {
     fingerprint: Option<String>,
     /// Local anchor for the crash multiplier, set when a round starts.
     crash_started: Option<Instant>,
+    /// Server-time anchor for the crash multiplier, when the server supplied
+    /// `started_at`.
+    crash_started_ms: Option<u64>,
+    /// Server clock minus local clock, in milliseconds, from `HELLO`/`PONG`.
+    server_offset_ms: i64,
+    /// True once a frontend has supplied a server timestamp.
+    clock_synced: bool,
     /// App screen shown when no game is open.
     screen: Screen,
     /// Last plays fetched with `history`.
@@ -83,11 +93,16 @@ impl ClientCore {
             connected: false,
             logged_in: None,
             pending: None,
+            pending_id: None,
+            next_request_id: 1,
             balance: None,
             account: None,
             host: None,
             fingerprint: None,
             crash_started: None,
+            crash_started_ms: None,
+            server_offset_ms: 0,
+            clock_synced: false,
             screen: Screen::Lobby,
             play_history: Vec::new(),
             login_error: None,
@@ -99,11 +114,19 @@ impl ClientCore {
         if !connected {
             self.logged_in = None;
             self.pending = None;
+            self.pending_id = None;
             self.crash_started = None;
+            self.crash_started_ms = None;
+            self.clock_synced = false;
             self.screen = Screen::Lobby;
         }
     }
 
+    /// The signed-in username, if any.
+    pub fn user(&self) -> Option<&str> {
+        self.logged_in.as_deref()
+    }
+
     pub fn set_logged_in(&mut self, user: Option<String>) {
         if user.is_some() {
             self.login_error = None;
@@ -147,7 +170,44 @@ impl ClientCore {
         self.board_effects()
     }
 
+    /// Record the server's clock and the local time it was received. The
+    /// offset is for display; cash-out still settles on the server.
+    pub fn set_server_time(&mut self, server_ms: u64) {
+        self.server_offset_ms = server_ms as i64 - unix_time_ms() as i64;
+        self.clock_synced = true;
+    }
+
+    /// The game server's clock, as this client currently estimates it.
+    pub fn server_now_ms(&self) -> u64 {
+        (unix_time_ms() as i64 + self.server_offset_ms).max(0) as u64
+    }
+
+    /// Allocate a correlation id for a request the adapter sends directly
+    /// (the terminal's login prompt bypasses `ClientCore`).
+    pub fn allocate_request_id(&mut self) -> u64 {
+        let id = self.next_request_id;
+        self.next_request_id = self.next_request_id.wrapping_add(1).max(1);
+        id
+    }
+
+    fn begin_request(&mut self, pending: Pending, payload: String) -> Effect {
+        let id = self.allocate_request_id();
+        self.pending = Some(pending);
+        self.pending_id = Some(id);
+        Effect::SendRequest { id, payload }
+    }
+
+    /// Route a reply by correlation id. A reply we no longer expect (a late
+    /// response after a timeout) is ignored instead of corrupting the board.
+    pub fn handle_reply_id(&mut self, id: u64, reply: &str) -> Vec<Effect> {
+        if self.pending_id != Some(id) {
+            return Vec::new();
+        }
+        self.handle_reply(reply)
+    }
+
     pub fn handle_reply(&mut self, reply: &str) -> Vec<Effect> {
+        self.pending_id = None;
         match self.pending.take() {
             Some(Pending::Spin) => match parse_spin_response(reply) {
                 Ok(result) => {
@@ -265,7 +325,8 @@ impl ClientCore {
                 }
             },
             Some(Pending::Ping) => {
-                if reply.trim() == "PONG" {
+                if let Some(server_ms) = parse_pong(reply) {
+                    self.set_server_time(server_ms);
                     print_line("Pong")
                 } else {
                     self.connected = false;
@@ -305,10 +366,8 @@ impl ClientCore {
         if self.game.begin_spin().is_err() {
             return Vec::new();
         }
-        self.pending = Some(Pending::Spin);
-
         let mut effects = self.board_effects();
-        effects.push(Effect::SendLine(request));
+        effects.push(self.begin_request(Pending::Spin, request));
         effects
     }
 
@@ -322,24 +381,24 @@ impl ClientCore {
                     return print_line("Not connected. Use 'connect <ip>:<port>' first.");
                 }
                 self.login_error = None;
-                self.pending = Some(Pending::Login { user: user.clone() });
-                vec![Effect::SendLine(format!("AUTH {user} {credential}"))]
+                vec![self.begin_request(
+                    Pending::Login { user: user.clone() },
+                    format!("AUTH {user} {credential}"),
+                )]
             }
             Command::Register { user, credential } => {
                 if !self.connected {
                     return print_line("Not connected. Use 'connect <ip>:<port>' first.");
                 }
                 self.login_error = None;
-                self.pending = Some(Pending::Register);
-                vec![Effect::SendLine(format!("REGISTER {user} {credential}"))]
+                vec![self.begin_request(Pending::Register, format!("REGISTER {user} {credential}"))]
             }
             Command::Games => vec![Effect::Print(game_lines(&self.games()))],
             Command::Ping => {
                 if !self.connected {
                     return print_line("Not connected. Use 'connect <ip>:<port>' first.");
                 }
-                self.pending = Some(Pending::Ping);
-                vec![Effect::SendLine("PING".to_string())]
+                vec![self.begin_request(Pending::Ping, "PING".to_string())]
             }
             Command::Echo(message) => {
                 if !self.connected {
@@ -348,8 +407,7 @@ impl ClientCore {
                 if message.trim().is_empty() {
                     return print_line("Usage: send <message>");
                 }
-                self.pending = Some(Pending::Echo);
-                vec![Effect::SendLine(message)]
+                vec![self.begin_request(Pending::Echo, message)]
             }
             Command::Info => self.info_effects(),
             Command::Play { game, bet } => self.play_game(&game, bet),
@@ -458,6 +516,7 @@ impl ClientCore {
 
     fn exit_game(&mut self) -> Vec<Effect> {
         self.crash_started = None;
+        self.crash_started_ms = None;
         self.screen = Screen::Lobby;
         self.game.end_game();
         vec![
@@ -475,19 +534,17 @@ impl ClientCore {
             return self.exit_game();
         };
         self.game.set_blackjack_status("forfeiting");
-        self.pending = Some(Pending::BlackjackForfeit);
-        vec![Effect::SendLine(format!(
-            "BLACKJACK_ACTION {} forfeit",
-            hand.session_id
-        ))]
+        vec![self.begin_request(
+            Pending::BlackjackForfeit,
+            format!("BLACKJACK_ACTION {} forfeit", hand.session_id),
+        )]
     }
 
     fn forfeit_crash(&mut self) -> Vec<Effect> {
         let Some(session) = self.game.crash_session_id() else {
             return self.exit_game();
         };
-        self.pending = Some(Pending::CrashForfeit);
-        vec![Effect::SendLine(format!("CRASH_FORFEIT {session}"))]
+        vec![self.begin_request(Pending::CrashForfeit, format!("CRASH_FORFEIT {session}"))]
     }
 
     fn place_roulette_chip_on(&mut self, target: BetTarget) -> Vec<Effect> {
@@ -533,10 +590,8 @@ impl ClientCore {
         if self.game.begin_spin().is_err() {
             return Vec::new();
         }
-        self.pending = Some(Pending::RouletteSpin);
-
         let mut effects = self.board_effects();
-        effects.push(Effect::SendLine(request));
+        effects.push(self.begin_request(Pending::RouletteSpin, request));
         effects
     }
 
@@ -566,9 +621,8 @@ impl ClientCore {
         }
 
         self.game.set_blackjack_status("dealing");
-        self.pending = Some(Pending::BlackjackStart);
         let mut effects = self.board_effects();
-        effects.push(Effect::SendLine(request));
+        effects.push(self.begin_request(Pending::BlackjackStart, request));
         effects
     }
 
@@ -582,15 +636,21 @@ impl ClientCore {
         if action == "double" && !hand.actions.iter().any(|available| available == "double") {
             return Vec::new();
         }
-        self.pending = Some(Pending::BlackjackAction);
-        vec![Effect::SendLine(format!(
-            "BLACKJACK_ACTION {} {}",
-            hand.session_id, action
-        ))]
+        vec![self.begin_request(
+            Pending::BlackjackAction,
+            format!("BLACKJACK_ACTION {} {}", hand.session_id, action),
+        )]
     }
 
     /// Redraw the rising multiplier. Called by the terminal loop on a timer.
     pub fn tick(&mut self) -> Vec<Effect> {
+        if self.clock_synced {
+            if let Some(started_ms) = self.crash_started_ms {
+                let now = unix_time_ms() as i64 + self.server_offset_ms;
+                let elapsed_ms = (now - started_ms as i64).max(0) as u64;
+                return self.tick_at(Duration::from_millis(elapsed_ms));
+            }
+        }
         let Some(started) = self.crash_started else {
             return Vec::new();
         };
@@ -619,12 +679,16 @@ impl ClientCore {
     }
 
     pub fn is_async(&self, line: &str) -> bool {
-        line.trim_start().starts_with("CRASH_BUSTED ")
+        let line = line.trim_start();
+        line.starts_with("CRASH_BUSTED ") || line.starts_with("crash.tick ")
     }
 
     /// Handle a server-initiated line. Returns `None` when the line is a normal
     /// request/response reply and belongs to `handle_reply`.
     pub fn handle_async_line(&mut self, line: &str) -> Option<Vec<Effect>> {
+        if let Some(tick) = line.trim_start().strip_prefix("crash.tick ") {
+            return Some(self.apply_crash_tick(tick));
+        }
         if !self.is_async(line) {
             return None;
         }
@@ -643,13 +707,43 @@ impl ClientCore {
             if self.crash_started.is_none() {
                 self.crash_started = Some(Instant::now());
             }
+            if state.started_at > 0 {
+                self.crash_started_ms = Some(state.started_at);
+            }
         } else {
             self.crash_started = None;
+            self.crash_started_ms = None;
         }
         self.game.apply_crash_state(state);
         self.board_effects()
     }
 
+    /// Apply `crash.tick session=<id> t=<server_ms> m=<multiplier>`.
+    fn apply_crash_tick(&mut self, tick: &str) -> Vec<Effect> {
+        let mut session = None;
+        let mut multiplier = None;
+        for token in tick.split_whitespace() {
+            if let Some(value) = token.strip_prefix("session=") {
+                session = Some(value);
+            } else if let Some(value) = token.strip_prefix("m=") {
+                multiplier = value.parse::<f64>().ok();
+            }
+        }
+        let Some(multiplier) = multiplier else {
+            return Vec::new();
+        };
+        if let Some(session) = session {
+            if self.game.crash_session_id().as_deref() != Some(session) {
+                return Vec::new();
+            }
+        }
+        if self.game.crash_status() != "running" {
+            return Vec::new();
+        }
+        self.game.set_crash_multiplier(multiplier);
+        self.board_effects()
+    }
+
     fn start_crash(&mut self) -> Vec<Effect> {
         let status = self.game.crash_status();
         if !matches!(status.as_str(), "ready" | "cashed" | "crashed" | "forfeit") {
@@ -671,9 +765,8 @@ impl ClientCore {
         }
 
         self.game.set_crash_status("starting");
-        self.pending = Some(Pending::CrashStart);
         let mut effects = self.board_effects();
-        effects.push(Effect::SendLine(request));
+        effects.push(self.begin_request(Pending::CrashStart, request));
         effects
     }
 
@@ -681,8 +774,7 @@ impl ClientCore {
         let Some(session) = self.game.crash_session_id() else {
             return Vec::new();
         };
-        self.pending = Some(Pending::CrashCashout);
-        vec![Effect::SendLine(format!("CRASH_CASHOUT {session}"))]
+        vec![self.begin_request(Pending::CrashCashout, format!("CRASH_CASHOUT {session}"))]
     }
 
     fn play_game(&mut self, game_type: &str, bet: Option<u64>) -> Vec<Effect> {
@@ -706,8 +798,7 @@ impl ClientCore {
                 }
 
                 let mut effects = self.board_effects();
-                self.pending = Some(Pending::Info);
-                effects.push(Effect::SendLine("INFO".to_string()));
+                effects.push(self.begin_request(Pending::Info, "INFO".to_string()));
                 effects
             }
             Err(_) => print_line("Failed to enter game"),
@@ -726,13 +817,12 @@ impl ClientCore {
         }
 
         self.screen = Screen::History;
-        self.pending = Some(Pending::History);
         let request = if limit == crate::history::DEFAULT_HISTORY {
             "HISTORY".to_string()
         } else {
             format!("HISTORY {limit}")
         };
-        vec![Effect::SendLine(request)]
+        vec![self.begin_request(Pending::History, request)]
     }
 
     fn info_effects(&mut self) -> Vec<Effect> {
@@ -754,8 +844,7 @@ impl ClientCore {
             ])),
         }
 
-        self.pending = Some(Pending::Info);
-        effects.push(Effect::SendLine("INFO".to_string()));
+        effects.push(self.begin_request(Pending::Info, "INFO".to_string()));
         effects
     }
 
@@ -809,7 +898,6 @@ impl ClientCore {
         }
         self.view().map(Effect::Render).into_iter().collect()
     }
-
 }
 
 fn auth_result(reply: &str) -> Result<(), String> {
diff --git a/src/client/games/manager.rs b/src/client/games/manager.rs
index 24ceeaa..d35308b 100644
--- a/src/client/games/manager.rs
+++ b/src/client/games/manager.rs
@@ -5,7 +5,7 @@ use super::roulette::RouletteGame;
 use super::slots::SlotsGame;
 use super::traits::{Game, GameError, GamePhase, GameState};
 use crate::blackjack::BlackjackState;
-use crate::crash::{payout, CrashState};
+use crate::crash::{CrashState, payout};
 use crate::roulette::Bets;
 use std::collections::HashMap;
 
@@ -244,9 +244,7 @@ impl GameManager {
 
     pub fn set_roulette_cursor(&mut self, cursor: &crate::client::games::roulette::Cursor) {
         if let Some(session) = self.current_session.as_mut() {
-            session
-                .data
-                .insert("cursor".to_string(), cursor.encoded());
+            session.data.insert("cursor".to_string(), cursor.encoded());
         }
     }
 
@@ -339,7 +337,7 @@ impl GameManager {
         };
         session.bet_amount = state.bet;
         session.data.remove("error");
-        for key in ["crash_point", "payout"] {
+        for key in ["crash_point", "payout", "commit", "seed"] {
             session.data.remove(key);
         }
         session
@@ -360,10 +358,21 @@ impl GameManager {
         session
             .data
             .insert("payout".to_string(), state.payout.to_string());
+        session
+            .data
+            .insert("started_at".to_string(), state.started_at.to_string());
+        if let Some(commit) = &state.commit {
+            session.data.insert("commit".to_string(), commit.clone());
+        }
+        if let Some(seed) = &state.seed {
+            session.data.insert("seed".to_string(), seed.clone());
+        }
         if let Some(crash_point) = state.crash_point {
+            // Keep full precision: the browser recomputes this from the
+            // revealed seed, and the GUI charts it.
             session
                 .data
-                .insert("crash_point".to_string(), format!("{crash_point:.2}"));
+                .insert("crash_point".to_string(), crash_point.to_string());
         }
     }
 
diff --git a/src/client/games/roulette.rs b/src/client/games/roulette.rs
index f0ed816..15cc6ed 100644
--- a/src/client/games/roulette.rs
+++ b/src/client/games/roulette.rs
@@ -1,6 +1,7 @@
 use super::traits::{Game, GameState};
 use crate::client::view::{RoulettePhase, RouletteView};
 use crate::roulette::{BetTarget, Bets, Outside, is_even, is_odd};
+use serde::{Deserialize, Serialize};
 
 pub const ROULETTE_BOARD_LINES: usize = 12;
 
@@ -21,7 +22,7 @@ const OUTSIDE_ORDER: [Outside; 6] = [
 
 pub struct RouletteGame;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Direction {
     Up,
     Down,
@@ -41,7 +42,7 @@ pub enum Direction {
 ///   odd,even   line between rows       split of the two numbers
 ///   even,even  corner of four cells    corner
 /// ```
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Cursor {
     Zero,
     Lattice { x: usize, y: usize },
@@ -67,7 +68,9 @@ impl Cursor {
         match parts.as_slice() {
             ["zero"] => Cursor::Zero,
             ["lattice", x, y] => match (x.parse::<usize>(), y.parse::<usize>()) {
-                (Ok(x), Ok(y)) if (1..=FELT_X_MAX).contains(&x) && (1..=FELT_Y_MAX).contains(&y) => {
+                (Ok(x), Ok(y))
+                    if (1..=FELT_X_MAX).contains(&x) && (1..=FELT_Y_MAX).contains(&y) =>
+                {
                     Cursor::Lattice { x, y }
                 }
                 _ => Cursor::default(),
diff --git a/src/client/transport.rs b/src/client/transport.rs
index 97c9227..60e7ab6 100644
--- a/src/client/transport.rs
+++ b/src/client/transport.rs
@@ -7,20 +7,27 @@
 use std::fmt;
 use std::io::{Read, Write};
 use std::net::TcpStream;
-use std::sync::mpsc;
 use std::sync::Arc;
+use std::sync::mpsc;
 use std::thread;
 use std::time::{Duration, Instant};
 
 use parking_lot::Mutex;
-use rustls::client::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier};
-use rustls::DigitallySignedStruct;
 use rusqlite::Connection;
+use rustls::DigitallySignedStruct;
+use rustls::client::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier};
 
 use crate::client::database;
-use crate::protocol::LineBuffer;
-use crate::tofu::{decide, spki_fingerprint, TrustDecision};
-use crate::version::{parse_hello, HelloReply, VERSION};
+use crate::protocol::{
+    FrameBuffer, Packet, parse_packet, request_line, write_frame as write_protocol_frame,
+};
+use crate::tofu::{TrustDecision, decide, spki_fingerprint};
+use crate::version::{HelloReply, VERSION, parse_hello};
+
+/// Reserved request ids for the transport handshake. Application requests
+/// start at 1, so the two ranges cannot collide on one connection.
+const HELLO_REQUEST_ID: u64 = u64::MAX;
+const AUTH_REQUEST_ID: u64 = u64::MAX - 1;
 
 /// How long to wait for TCP + TLS before giving up.
 const CONNECT_TIMEOUT: Duration = Duration::from_secs(10);
@@ -43,6 +50,8 @@ pub struct Connected {
     pub server_version: String,
     pub latest: String,
     pub url: String,
+    /// Server Unix time reported by `HELLO`, milliseconds.
+    pub server_time: u64,
     /// Round trip of the HELLO exchange.
     pub elapsed: Duration,
 }
@@ -51,10 +60,7 @@ pub struct Connected {
 pub enum TransportError {
     Timeout,
     TrustDeclined,
-    KeyChanged {
-        expected: String,
-        observed: String,
-    },
+    KeyChanged { expected: String, observed: String },
     VersionMismatch(String),
     Closed,
     Unexpected(String),
@@ -121,7 +127,7 @@ pub fn connect(
                 return Err(TransportError::KeyChanged {
                     expected,
                     observed: actual,
-                })
+                });
             }
         }
     }
@@ -131,12 +137,7 @@ pub fn connect(
         .map_err(io_failure)?;
 
     let start = Instant::now();
-    tls.write_line(&format!("HELLO {VERSION}"))
-        .map_err(io_failure)?;
-    let mut response = String::new();
-    if tls.read_line(&mut response).map_err(io_failure)? == 0 {
-        return Err(TransportError::Closed);
-    }
+    let response = exchange(&mut tls, HELLO_REQUEST_ID, &format!("HELLO {VERSION}"))?;
     let elapsed = start.elapsed();
 
     let response = response.trim();
@@ -151,10 +152,11 @@ pub fn connect(
     let mut user = None;
     let mut auth_error = None;
     if let Some((username, password)) = database::get_credentials(conn, &observed) {
-        tls.write_line(&format!("AUTH {username} {password}"))
-            .map_err(io_failure)?;
-        let mut auth = String::new();
-        tls.read_line(&mut auth).map_err(io_failure)?;
+        let auth = exchange(
+            &mut tls,
+            AUTH_REQUEST_ID,
+            &format!("AUTH {username} {password}"),
+        )?;
         if auth.trim().starts_with("OK") {
             user = Some(username);
         } else {
@@ -169,19 +171,31 @@ pub fn connect(
         server_version: hello.version,
         latest: hello.latest,
         url: hello.url,
+        server_time: hello.time,
         elapsed,
     })
 }
 
+/// Send one request and wait for the reply with the same id, ignoring events
+/// that arrive in between. Used only for the handshake.
+fn exchange(stream: &mut TlsStream, id: u64, payload: &str) -> Result<String, TransportError> {
+    stream
+        .write_request(id, None, payload)
+        .map_err(io_failure)?;
+    loop {
+        match stream.read_packet().map_err(io_failure)? {
+            None => return Err(TransportError::Closed),
+            Some(Packet::Reply { id: reply_id, body }) if reply_id == id => return Ok(body),
+            Some(Packet::Reply { .. }) | Some(Packet::Event { .. }) => continue,
+        }
+    }
+}
+
 /// TCP + TLS on a thread so a blocked handshake can time out.
 fn tls_connect(addr: &str) -> Result<(TlsStream, Option<String>), TransportError> {
     let (sender, receiver) = mpsc::channel();
     let addr = addr.to_string();
-    let server_name = addr
-        .split(':')
-        .next()
-        .unwrap_or("127.0.0.1")
-        .to_string();
+    let server_name = addr.split(':').next().unwrap_or("127.0.0.1").to_string();
 
     thread::spawn(move || {
         let outcome = (|| -> Result<(TlsStream, Option<String>), TransportError> {
@@ -241,7 +255,7 @@ impl TlsConnector {
             session: Arc::new(Mutex::new(Session {
                 sock,
                 tls: connection,
-                lines: LineBuffer::new(),
+                frames: FrameBuffer::new(),
                 read_timeout: Some(READ_TIMEOUT),
             })),
         })
@@ -268,8 +282,9 @@ impl ServerCertVerifier for RecordingVerifier {
         _ocsp_response: &[u8],
         _now: std::time::SystemTime,
     ) -> Result<ServerCertVerified, rustls::Error> {
-        let fingerprint = spki_fingerprint(&end_entity.0)
-            .map_err(|error| rustls::Error::General(format!("certificate parse failed: {error}")))?;
+        let fingerprint = spki_fingerprint(&end_entity.0).map_err(|error| {
+            rustls::Error::General(format!("certificate parse failed: {error}"))
+        })?;
         *self.observed.lock() = Some(fingerprint);
         Ok(ServerCertVerified::assertion())
     }
@@ -313,7 +328,7 @@ impl ServerCertVerifier for RecordingVerifier {
 struct Session {
     sock: TcpStream,
     tls: rustls::ClientConnection,
-    lines: LineBuffer,
+    frames: FrameBuffer,
     read_timeout: Option<Duration>,
 }
 
@@ -329,37 +344,58 @@ pub struct TlsStream {
 }
 
 impl TlsStream {
-    pub fn read_line(&mut self, buf: &mut String) -> std::io::Result<usize> {
+    /// Write one enveloped request. Application code allocates `id`.
+    pub fn write_request(
+        &mut self,
+        id: u64,
+        idem: Option<&str>,
+        payload: &str,
+    ) -> std::io::Result<()> {
+        self.write_frame(&request_line(id, idem, payload))
+    }
+
+    /// Write one raw frame payload.
+    pub fn write_frame(&mut self, payload: &str) -> std::io::Result<()> {
+        let mut s = self.session.lock();
+        write_protocol_frame(&mut s.tls.writer(), payload)?;
+        s.drive()
+    }
+
+    /// Block until one whole frame arrives.
+    pub fn read_frame(&mut self) -> std::io::Result<Option<String>> {
         let mut s = self.session.lock();
         loop {
-            if let Some(line) = s.lines.next_line() {
-                buf.push_str(&line);
-                buf.push('\n');
-                return Ok(line.len() + 1);
+            match s.frames.next_frame() {
+                Some(Ok(frame)) => return Ok(Some(frame)),
+                Some(Err(error)) => {
+                    return Err(std::io::Error::new(std::io::ErrorKind::InvalidData, error));
+                }
+                None => {}
             }
 
             let mut chunk = [0u8; 4096];
             match s.tls.reader().read(&mut chunk) {
-                Ok(0) => {
-                    if let Some(rest) = s.lines.take_rest() {
-                        let read = rest.len();
-                        buf.push_str(&rest);
-                        return Ok(read);
-                    }
-                    return Ok(0);
-                }
-                Ok(n) => s.lines.push(&chunk[..n]),
+                Ok(0) => return Ok(None),
+                Ok(n) => s.frames.push(&chunk[..n]),
                 Err(error) if error.kind() == std::io::ErrorKind::WouldBlock => s.drive()?,
                 Err(error) => return Err(error),
             }
         }
     }
 
-    pub fn write_line(&mut self, message: &str) -> std::io::Result<()> {
-        let mut s = self.session.lock();
-        s.tls.writer().write_all(message.as_bytes())?;
-        s.tls.writer().write_all(b"\n")?;
-        s.drive()
+    /// Block until one `RES` or `EVT` arrives.
+    pub fn read_packet(&mut self) -> std::io::Result<Option<Packet>> {
+        loop {
+            let Some(frame) = self.read_frame()? else {
+                return Ok(None);
+            };
+            match parse_packet(&frame) {
+                Ok(packet) => return Ok(Some(packet)),
+                Err(error) => {
+                    return Err(std::io::Error::new(std::io::ErrorKind::InvalidData, error));
+                }
+            }
+        }
     }
 
     pub fn set_read_timeout(&self, duration: Option<Duration>) -> std::io::Result<()> {
@@ -368,24 +404,36 @@ impl TlsStream {
         s.sock.set_read_timeout(duration)
     }
 
-    /// Return one complete line if the socket already has one, without
-    /// blocking. Used to pick up server pushes between requests.
-    pub fn read_available_line(&mut self) -> std::io::Result<Option<String>> {
+    /// Return one packet if the socket already has one, without blocking.
+    /// Used to pick up server pushes between requests.
+    pub fn read_available_packet(&mut self) -> std::io::Result<Option<Packet>> {
         let mut s = self.session.lock();
-        if let Some(line) = s.lines.next_line() {
-            return Ok(Some(line));
-        }
 
         // `set_read_timeout(Some(0))` is rejected by std, so poll with the
         // shortest timeout the socket accepts instead of a nonblocking mode.
         s.sock
             .set_read_timeout(Some(std::time::Duration::from_millis(1)))?;
-        let drained = (|| -> std::io::Result<()> {
+        let drained = (|| -> std::io::Result<Option<Packet>> {
             loop {
+                match s.frames.next_frame() {
+                    Some(Ok(frame)) => {
+                        return match parse_packet(&frame) {
+                            Ok(packet) => Ok(Some(packet)),
+                            Err(error) => {
+                                Err(std::io::Error::new(std::io::ErrorKind::InvalidData, error))
+                            }
+                        };
+                    }
+                    Some(Err(error)) => {
+                        return Err(std::io::Error::new(std::io::ErrorKind::InvalidData, error));
+                    }
+                    None => {}
+                }
+
                 let mut buf = [0u8; 4096];
                 match s.tls.reader().read(&mut buf) {
-                    Ok(0) => return Ok(()),
-                    Ok(n) => s.lines.push(&buf[..n]),
+                    Ok(0) => return Ok(None),
+                    Ok(n) => s.frames.push(&buf[..n]),
                     // The reader only drains plaintext rustls has already
                     // decrypted; `drive` moves bytes off the socket.
                     Err(error) if error.kind() == std::io::ErrorKind::WouldBlock => {
@@ -397,7 +445,7 @@ impl TlsStream {
                                     std::io::ErrorKind::WouldBlock | std::io::ErrorKind::TimedOut
                                 ) =>
                             {
-                                return Ok(());
+                                return Ok(None);
                             }
                             Err(error) => return Err(error),
                         }
@@ -408,15 +456,14 @@ impl TlsStream {
                             std::io::ErrorKind::WouldBlock | std::io::ErrorKind::TimedOut
                         ) =>
                     {
-                        return Ok(());
+                        return Ok(None);
                     }
                     Err(error) => return Err(error),
                 }
             }
         })();
         s.sock.set_read_timeout(s.read_timeout)?;
-        drained?;
-        Ok(s.lines.next_line())
+        drained
     }
 }
 
diff --git a/src/client/view.rs b/src/client/view.rs
index 4615720..0886d64 100644
--- a/src/client/view.rs
+++ b/src/client/view.rs
@@ -7,15 +7,17 @@ use crate::blackjack::BlackjackState;
 use crate::client::games::roulette::{Cursor, Direction};
 use crate::client::games::traits::{GamePhase, GameState};
 use crate::roulette::{BetTarget, Bets};
+use serde::{Deserialize, Serialize};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
 pub enum RoulettePhase {
     Placing,
     Spinning,
     Result,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct RouletteView {
     pub bet_amount: u64,
     pub balance: Option<i64>,
@@ -51,7 +53,10 @@ impl RouletteView {
             Some("result") => RoulettePhase::Result,
             _ => RoulettePhase::Placing,
         };
-        let number = state.data.get("number").and_then(|value| value.parse().ok());
+        let number = state
+            .data
+            .get("number")
+            .and_then(|value| value.parse().ok());
         let color = state.data.get("color").cloned();
         let winnings = state
             .data
@@ -82,14 +87,15 @@ impl RouletteView {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
 pub enum SlotsPhase {
     Ready,
     Spinning,
     Result,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct SlotsView {
     pub bet: u64,
     pub balance: Option<i64>,
@@ -149,7 +155,7 @@ impl SlotsView {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct BlackjackView {
     pub status: String,
     pub balance: Option<i64>,
@@ -186,7 +192,7 @@ impl BlackjackView {
     }
 }
 
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct CrashView {
     pub status: String,
     pub balance: Option<i64>,
@@ -195,6 +201,11 @@ pub struct CrashView {
     pub potential: u64,
     pub crash_point: Option<f64>,
     pub payout: u64,
+    pub started_at: u64,
+    /// `sha256(seed)` for this round, before it ends.
+    pub commit: Option<String>,
+    /// The revealed seed, after the round ends.
+    pub seed: Option<String>,
     pub error: Option<String>,
 }
 
@@ -232,6 +243,13 @@ impl CrashView {
                 .get("payout")
                 .and_then(|value| value.parse::<u64>().ok())
                 .unwrap_or(0),
+            started_at: state
+                .data
+                .get("started_at")
+                .and_then(|value| value.parse::<u64>().ok())
+                .unwrap_or(0),
+            commit: state.data.get("commit").cloned(),
+            seed: state.data.get("seed").cloned(),
             error: state
                 .data
                 .get("error")
@@ -242,7 +260,7 @@ impl CrashView {
 }
 
 /// The lobby: who is logged in, the balance, and what can be played.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct LobbyView {
     pub connected: bool,
     pub user: Option<String>,
@@ -254,13 +272,14 @@ pub struct LobbyView {
 }
 
 /// The play log, already parsed.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct HistoryView {
     pub records: Vec<crate::history::PlayRecord>,
 }
 
 /// Everything a frontend can draw.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "screen", rename_all = "snake_case")]
 pub enum View {
     Lobby(LobbyView),
     History(HistoryView),
@@ -271,17 +290,28 @@ pub enum View {
 }
 
 /// Semantic input. Frontends turn keys and clicks into these.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Command {
     /// The credential is already hashed by the frontend.
-    Login { user: String, credential: String },
+    Login {
+        user: String,
+        credential: String,
+    },
     Games,
     Ping,
     Echo(String),
     Info,
-    Register { user: String, credential: String },
-    Play { game: String, bet: Option<u64> },
-    History { limit: u32 },
+    Register {
+        user: String,
+        credential: String,
+    },
+    Play {
+        game: String,
+        bet: Option<u64>,
+    },
+    History {
+        limit: u32,
+    },
     ShowLobby,
     Logout,
     SetBet(u64),
diff --git a/src/crash.rs b/src/crash.rs
index 9d6e98c..40b8743 100644
--- a/src/crash.rs
+++ b/src/crash.rs
@@ -6,6 +6,7 @@
 //! clock, never from anything the client sends.
 
 use serde::{Deserialize, Serialize};
+use sha2::{Digest, Sha256};
 use std::time::Duration;
 
 /// `exp(GROWTH_RATE * t)` doubles the multiplier every five seconds.
@@ -47,6 +48,53 @@ pub fn crash_point_from_uniform(u: f64) -> f64 {
     ((1.0 - HOUSE_EDGE) / (1.0 - u)).clamp(1.0, MAX_MULTIPLIER)
 }
 
+/// How many bytes a round seed contains. The first eight bytes choose the
+/// crash point; the rest are revealed and hashed with it.
+pub const SEED_LEN: usize = 32;
+
+/// Hex-encoded SHA-256 of a round seed, sent before the round starts.
+pub fn commit_seed(seed: &[u8]) -> String {
+    let digest = Sha256::digest(seed);
+    format!("{digest:x}")
+}
+
+/// Uniform draw encoded by a seed: the first eight bytes, big-endian.
+pub fn seed_to_uniform(seed: &[u8]) -> f64 {
+    let mut bytes = [0u8; 8];
+    let take = seed.len().min(8);
+    bytes[..take].copy_from_slice(&seed[..take]);
+    u64::from_be_bytes(bytes) as f64 / 18_446_744_073_709_551_616.0
+}
+
+/// The crash point a seed commits to. A client recomputes this after the
+/// reveal and checks it against the published commit.
+pub fn crash_point_from_seed(seed: &[u8]) -> f64 {
+    crash_point_from_uniform(seed_to_uniform(seed))
+}
+
+/// Decode a lowercase or uppercase hex seed. Returns `None` for odd lengths,
+/// bad digits or a seed that is not exactly [`SEED_LEN`] bytes.
+pub fn seed_from_hex(raw: &str) -> Option<Vec<u8>> {
+    if raw.len() != SEED_LEN * 2 {
+        return None;
+    }
+    let mut seed = Vec::with_capacity(SEED_LEN);
+    for pair in raw.as_bytes().chunks_exact(2) {
+        let high = (pair[0] as char).to_digit(16)?;
+        let low = (pair[1] as char).to_digit(16)?;
+        seed.push((high * 16 + low) as u8);
+    }
+    Some(seed)
+}
+
+/// Check a revealed seed against the commit published before the round.
+pub fn verify_seed(seed_hex: &str, commit: &str) -> bool {
+    let Some(seed) = seed_from_hex(seed_hex) else {
+        return false;
+    };
+    commit_seed(&seed).eq_ignore_ascii_case(commit)
+}
+
 /// Whole-Kr cashout value. Balances are integers, so the payout is floored.
 pub fn payout(bet: u64, multiplier: f64) -> u64 {
     if bet == 0 || !multiplier.is_finite() || multiplier <= 0.0 {
@@ -72,10 +120,16 @@ pub struct CrashState {
     pub multiplier: f64,
     /// `floor(bet * multiplier)` for the value above.
     pub potential: u64,
+    /// Server Unix time when the round started, milliseconds.
+    pub started_at: u64,
     /// Hidden until the round ends.
     pub crash_point: Option<f64>,
     pub payout: u64,
     pub result: String,
+    /// `sha256(seed)`, present for the whole round.
+    pub commit: Option<String>,
+    /// The seed itself, present only after the round ends.
+    pub seed: Option<String>,
 }
 
 impl CrashState {
diff --git a/src/protocol.rs b/src/protocol.rs
index 11f54a1..e838b08 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -1,16 +1,60 @@
-//! Newline-delimited protocol helpers shared by the client and server.
+//! Protocol v5: bounded frames and the request/reply/event envelope.
 //!
-//! TLS reads can return more than one line at a time. Keeping the leftover
-//! bytes is essential: dropping them silently loses the next message.
+//! Every packet is `[u32 length][UTF-8 payload]`. The length is big-endian and
+//! capped, so a peer cannot make the reader allocate without bound. Inside a
+//! frame the payload is text:
+//!
+//! ```text
+//! REQ <id> [idem=<token>] <command>
+//! RES <id> <body>
+//! EVT <seq> <body>
+//! ```
+//!
+//! The command and body grammar is the same text protocol the games already
+//! use (`HELLO`, `PLAY_START`, `GAME_RESULT`, ...). The envelope only adds
+//! correlation, event numbering and a hard size limit.
+
+use std::fmt;
+use std::io::{self, Read, Write};
+
+/// Largest payload a peer may send in one frame. A game message is a few
+/// hundred bytes; 64 KiB is generous and still bounds the reader.
+pub const MAX_FRAME_LEN: usize = 64 * 1024;
+
+/// How many request ids a connection remembers for idempotent retries.
+pub const REPLAY_CACHE_LEN: usize = 256;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FrameError {
+    /// The declared payload length exceeds [`MAX_FRAME_LEN`].
+    TooLarge(usize),
+    /// The payload was not valid UTF-8.
+    InvalidUtf8,
+}
+
+impl fmt::Display for FrameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            FrameError::TooLarge(length) => {
+                write!(
+                    f,
+                    "frame of {length} bytes exceeds the {MAX_FRAME_LEN}-byte limit"
+                )
+            }
+            FrameError::InvalidUtf8 => write!(f, "frame payload is not valid UTF-8"),
+        }
+    }
+}
 
-use std::io::{self, Read};
+impl std::error::Error for FrameError {}
 
+/// A bounded frame decoder. Feed it bytes from a socket, take whole frames.
 #[derive(Debug, Default)]
-pub struct LineBuffer {
+pub struct FrameBuffer {
     buffer: Vec<u8>,
 }
 
-impl LineBuffer {
+impl FrameBuffer {
     pub fn new() -> Self {
         Self::default()
     }
@@ -19,46 +63,172 @@ impl LineBuffer {
         self.buffer.extend_from_slice(bytes);
     }
 
-    /// Return the next complete line, including a line that ended at EOF.
-    pub fn next_line(&mut self) -> Option<String> {
-        let end = self.buffer.iter().position(|byte| *byte == b'\n')?;
-        let mut line: Vec<u8> = self.buffer.drain(..=end).collect();
-        line.pop(); // '\n'
-        if line.last() == Some(&b'\r') {
-            line.pop();
+    /// Return the next complete frame, if the buffer holds one.
+    ///
+    /// A declared length above the limit is reported immediately instead of
+    /// waiting for bytes that will never be accepted; the caller should close
+    /// the connection.
+    pub fn next_frame(&mut self) -> Option<Result<String, FrameError>> {
+        if self.buffer.len() < 4 {
+            return None;
         }
-        Some(String::from_utf8_lossy(&line).into_owned())
-    }
 
-    /// Return the unterminated remainder at EOF, if any.
-    pub fn take_rest(&mut self) -> Option<String> {
-        if self.buffer.is_empty() {
+        let length = u32::from_be_bytes([
+            self.buffer[0],
+            self.buffer[1],
+            self.buffer[2],
+            self.buffer[3],
+        ]) as usize;
+
+        if length > MAX_FRAME_LEN {
+            self.buffer.clear();
+            return Some(Err(FrameError::TooLarge(length)));
+        }
+        if self.buffer.len() < 4 + length {
             return None;
         }
-        let mut rest = std::mem::take(&mut self.buffer);
-        if rest.last() == Some(&b'\r') {
-            rest.pop();
+
+        let payload: Vec<u8> = self.buffer[4..4 + length].to_vec();
+        self.buffer.drain(..4 + length);
+        match String::from_utf8(payload) {
+            Ok(text) => Some(Ok(text)),
+            Err(_) => Some(Err(FrameError::InvalidUtf8)),
         }
-        Some(String::from_utf8_lossy(&rest).into_owned())
     }
 
-    /// Read one line from a blocking reader, preserving any extra lines for
-    /// the next call. Returns `None` at EOF with nothing buffered.
-    pub fn read_line<R: Read>(&mut self, reader: &mut R) -> io::Result<Option<String>> {
+    /// Read one frame from a blocking reader, preserving leftover bytes.
+    /// `None` means EOF with no complete frame buffered.
+    pub fn read_frame<R: Read>(&mut self, reader: &mut R) -> io::Result<Option<String>> {
         loop {
-            if let Some(line) = self.next_line() {
-                return Ok(Some(line));
+            match self.next_frame() {
+                Some(Ok(frame)) => return Ok(Some(frame)),
+                Some(Err(error)) => return Err(io::Error::new(io::ErrorKind::InvalidData, error)),
+                None => {}
             }
 
             let mut chunk = [0u8; 4096];
             match reader.read(&mut chunk) {
-                Ok(0) => return Ok(self.take_rest()),
+                Ok(0) => return Ok(None),
                 Ok(n) => self.push(&chunk[..n]),
                 Err(error) if error.kind() == io::ErrorKind::Interrupted => continue,
                 Err(error) => return Err(error),
             }
         }
     }
+
+    /// True when a partial frame is buffered (used by tests and diagnostics).
+    pub fn is_empty(&self) -> bool {
+        self.buffer.is_empty()
+    }
+}
+
+/// Encode one payload as a length-prefixed frame.
+pub fn encode_frame(payload: &str) -> Vec<u8> {
+    let length = payload.len() as u32;
+    let mut bytes = Vec::with_capacity(4 + payload.len());
+    bytes.extend_from_slice(&length.to_be_bytes());
+    bytes.extend_from_slice(payload.as_bytes());
+    bytes
+}
+
+/// Write one payload as a length-prefixed frame.
+pub fn write_frame<W: Write>(writer: &mut W, payload: &str) -> io::Result<()> {
+    writer.write_all(&encode_frame(payload))?;
+    writer.flush()
+}
+
+/// One client request. `id` is the correlation key; `idem` is optional
+/// metadata for logs and a future cross-connection cache.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Request {
+    pub id: u64,
+    pub idem: Option<String>,
+    pub payload: String,
+}
+
+/// A frame received by a client.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Packet {
+    Reply { id: u64, body: String },
+    Event { seq: u64, body: String },
+}
+
+pub fn request_line(id: u64, idem: Option<&str>, payload: &str) -> String {
+    match idem {
+        Some(idem) if !idem.is_empty() => format!("REQ {id} idem={idem} {payload}"),
+        _ => format!("REQ {id} {payload}"),
+    }
+}
+
+pub fn reply_line(id: u64, body: &str) -> String {
+    format!("RES {id} {body}")
+}
+
+pub fn event_line(seq: u64, body: &str) -> String {
+    format!("EVT {seq} {body}")
+}
+
+/// Parse a `REQ` payload. Errors are safe to return to the peer.
+pub fn parse_request(frame: &str) -> Result<Request, String> {
+    let frame = frame.trim_end();
+    let rest = frame
+        .strip_prefix("REQ ")
+        .ok_or_else(|| "Malformed request: expected REQ".to_string())?;
+
+    let (id_token, mut rest) = split_token(rest);
+    let id: u64 = id_token
+        .parse()
+        .map_err(|_| "Malformed request id".to_string())?;
+
+    let mut idem = None;
+    let (next, after) = split_token(rest);
+    if let Some(value) = next.strip_prefix("idem=") {
+        if value.is_empty() {
+            return Err("Malformed idempotency key".to_string());
+        }
+        idem = Some(value.to_string());
+        rest = after;
+    }
+
+    Ok(Request {
+        id,
+        idem,
+        payload: rest.to_string(),
+    })
+}
+
+/// Parse a `RES` or `EVT` payload on the client side.
+pub fn parse_packet(frame: &str) -> Result<Packet, String> {
+    let frame = frame.trim_end();
+    if let Some(rest) = frame.strip_prefix("RES ") {
+        let (id_token, body) = split_token(rest);
+        let id: u64 = id_token
+            .parse()
+            .map_err(|_| "Malformed reply id".to_string())?;
+        return Ok(Packet::Reply {
+            id,
+            body: body.to_string(),
+        });
+    }
+    if let Some(rest) = frame.strip_prefix("EVT ") {
+        let (seq_token, body) = split_token(rest);
+        let seq: u64 = seq_token
+            .parse()
+            .map_err(|_| "Malformed event sequence".to_string())?;
+        return Ok(Packet::Event {
+            seq,
+            body: body.to_string(),
+        });
+    }
+    Err(format!("Unexpected packet: {frame}"))
+}
+
+fn split_token(rest: &str) -> (&str, &str) {
+    let rest = rest.trim_start();
+    match rest.find(' ') {
+        Some(index) => (&rest[..index], rest[index + 1..].trim_start()),
+        None => (rest, ""),
+    }
 }
 
 /// A stable, user-facing message for a failed request.
diff --git a/src/server/core.rs b/src/server/core.rs
index 3cd6469..0b2efb4 100644
--- a/src/server/core.rs
+++ b/src/server/core.rs
@@ -1,22 +1,26 @@
-use bcrypt::{hash, verify, DEFAULT_COST};
+use bcrypt::{DEFAULT_COST, hash, verify};
 use rusqlite::Connection;
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::sync::Arc;
 
 use crate::blackjack::BlackjackState;
 use crate::crash::CrashState;
+use crate::protocol::{REPLAY_CACHE_LEN, Request};
 use crate::server::database;
-use crate::version::{download_url, hello_line, Version, VERSION};
 use crate::server::games::blackjack::{BlackjackGame, BlackjackHand};
 use crate::server::games::crash::{Clock, CrashGame, CrashRound, RealClock};
 use crate::server::games::registry::GameRegistry;
 use crate::server::games::session::SessionManager;
 use crate::server::games::traits::{GameError, GamePhase, GameState};
+use crate::version::{VERSION, Version, download_url, hello_line, pong_line, unix_time_ms};
 
 #[derive(Debug, Default)]
 pub struct ConnectionState {
     user: Option<String>,
     greeted: bool,
+    /// Last replies on this connection, oldest first. Request ids are unique
+    /// while cached, so a retried request replays its first result.
+    replays: VecDeque<(u64, String, String)>,
 }
 
 /// Settle reservations left behind by a previous process.
@@ -39,6 +43,27 @@ impl ConnectionState {
     pub fn greeted(&self) -> bool {
         self.greeted
     }
+
+    fn replay(&self, id: u64, payload: &str) -> Option<Result<String, String>> {
+        self.replays
+            .iter()
+            .find(|(cached_id, _, _)| *cached_id == id)
+            .map(|(_, cached_payload, reply)| {
+                if cached_payload == payload {
+                    Ok(reply.clone())
+                } else {
+                    Err("ERROR Request id reused with a different command".to_string())
+                }
+            })
+    }
+
+    fn remember(&mut self, id: u64, payload: &str, reply: &str) {
+        if self.replays.len() >= REPLAY_CACHE_LEN {
+            self.replays.pop_front();
+        }
+        self.replays
+            .push_back((id, payload.to_string(), reply.to_string()));
+    }
 }
 
 pub struct ServerCore {
@@ -49,6 +74,8 @@ pub struct ServerCore {
     blackjack: BlackjackGame,
     crash: CrashGame,
     clock: Arc<dyn Clock>,
+    /// Last time a crash tick was pushed, in seconds on the game clock.
+    last_tick: HashMap<String, f64>,
 }
 
 impl ServerCore {
@@ -65,6 +92,7 @@ impl ServerCore {
             blackjack: BlackjackGame::new(),
             crash: CrashGame::new(),
             clock: Arc::new(RealClock::new()),
+            last_tick: HashMap::new(),
         }
     }
 
@@ -96,6 +124,21 @@ impl ServerCore {
         Ok(Self::new(conn))
     }
 
+    /// Handle one enveloped request, replaying a cached reply for a repeated
+    /// request id. The payload grammar is unchanged; the envelope only adds
+    /// correlation and idempotency.
+    pub fn handle_request(&mut self, state: &mut ConnectionState, request: &Request) -> String {
+        if let Some(reply) = state.replay(request.id, &request.payload) {
+            return match reply {
+                Ok(reply) => reply,
+                Err(message) => message,
+            };
+        }
+        let reply = self.handle_message(state, &request.payload);
+        state.remember(request.id, &request.payload, &reply);
+        reply
+    }
+
     pub fn handle_message(&mut self, state: &mut ConnectionState, msg: &str) -> String {
         let parts: Vec<&str> = msg.splitn(5, ' ').collect();
 
@@ -201,7 +244,7 @@ impl ServerCore {
                     }
                 }
             }
-            "PING" => "PONG".to_string(),
+            "PING" => pong_line(unix_time_ms()),
             "INFO" => self.handle_info(state),
             _ => msg.to_string(),
         }
@@ -212,7 +255,8 @@ impl ServerCore {
             return "ERROR Invalid HELLO format. Usage: HELLO <version>".to_string();
         }
 
-        let (Some(client), Some(server)) = (Version::parse(parts[1]), Version::parse(VERSION)) else {
+        let (Some(client), Some(server)) = (Version::parse(parts[1]), Version::parse(VERSION))
+        else {
             return "ERROR Invalid version".to_string();
         };
 
@@ -225,7 +269,7 @@ impl ServerCore {
         }
 
         state.greeted = true;
-        hello_line(VERSION, VERSION, &download_url())
+        hello_line(VERSION, VERSION, &download_url(), unix_time_ms())
     }
 
     fn handle_register(&mut self, username: &str, credential: &str) -> String {
@@ -529,8 +573,8 @@ impl ServerCore {
 
         // The session is the audit guard for the deduction, so it exists before
         // the balance is touched.
-        let crash_point = self.crash.next_crash_point();
-        let round = CrashRound::new(bet as u64, crash_point, self.clock.now());
+        let seed = self.crash.next_seed();
+        let round = CrashRound::new(bet as u64, seed, self.clock.now(), unix_time_ms());
         let mut data = HashMap::new();
         data.insert("round".to_string(), round.to_json());
         data.insert("balance".to_string(), balance.to_string());
@@ -643,11 +687,27 @@ impl ServerCore {
             if !round.is_running() {
                 continue;
             }
-            let elapsed = (self.clock.now() - round.started_at).max(0.0);
-            if crate::crash::multiplier_at_secs(elapsed) < round.crash_point {
+            let now = self.clock.now();
+            let elapsed = (now - round.started_at).max(0.0);
+            let multiplier = crate::crash::multiplier_at_secs(elapsed);
+            if multiplier < round.crash_point {
+                let last = self
+                    .last_tick
+                    .get(&session.session_id)
+                    .copied()
+                    .unwrap_or(f64::NEG_INFINITY);
+                if now - last >= 0.1 {
+                    self.last_tick.insert(session.session_id.clone(), now);
+                    out.push(format!(
+                        "crash.tick session={} t={} m={multiplier:.4}",
+                        session.session_id,
+                        unix_time_ms()
+                    ));
+                }
                 continue;
             }
             round.crash();
+            self.last_tick.remove(&session.session_id);
             match self.settle_crash(user, &session.session_id, &round, 0) {
                 Ok(balance) => {
                     let state = round.state(&session.session_id, balance);
@@ -678,6 +738,7 @@ impl ServerCore {
             payout as i64,
             &details,
         );
+        self.last_tick.remove(session_id);
         let _ = self.sessions.remove_session(session_id);
         result.map_err(|error| error.to_string())
     }
diff --git a/src/server/games/crash.rs b/src/server/games/crash.rs
index ba73c7f..1728afc 100644
--- a/src/server/games/crash.rs
+++ b/src/server/games/crash.rs
@@ -1,5 +1,8 @@
 use super::traits::{Game, GameError, GamePhase, GameResult, GameState};
-use crate::crash::{crash_point_from_uniform, payout, CrashState};
+use crate::crash::{
+    CrashState, SEED_LEN, commit_seed, crash_point_from_seed, payout, seed_to_uniform,
+};
+use rand::RngCore;
 use serde::{Deserialize, Serialize};
 use std::collections::{HashMap, VecDeque};
 use std::sync::{Arc, Mutex};
@@ -64,7 +67,14 @@ pub struct CrashRound {
     pub bet: u64,
     /// Drawn at start, revealed only when the round ends.
     pub crash_point: f64,
+    /// The 32 random bytes the crash point commits to, hex encoded. Kept on
+    /// the server until the round ends.
+    pub seed: String,
+    /// `sha256(seed)` in hex, sent with the start reply.
+    pub commit: String,
     pub started_at: f64,
+    /// Server Unix time at start, milliseconds, for clock sync.
+    pub started_at_ms: u64,
     /// `running`, `cashed`, `crashed` or `forfeit`.
     pub phase: String,
     pub result: String,
@@ -74,11 +84,15 @@ pub struct CrashRound {
 }
 
 impl CrashRound {
-    pub fn new(bet: u64, crash_point: f64, started_at: f64) -> Self {
+    pub fn new(bet: u64, seed: [u8; SEED_LEN], started_at: f64, started_at_ms: u64) -> Self {
+        let crash_point = crash_point_from_seed(&seed);
         Self {
             bet,
             crash_point,
+            seed: seed_hex(&seed),
+            commit: commit_seed(&seed),
             started_at,
+            started_at_ms,
             phase: "running".to_string(),
             result: "playing".to_string(),
             multiplier: 1.0,
@@ -120,6 +134,7 @@ impl CrashRound {
             balance,
             multiplier: self.multiplier,
             potential: payout(self.bet, self.multiplier),
+            started_at: self.started_at_ms,
             crash_point: if self.is_running() {
                 None
             } else {
@@ -127,6 +142,12 @@ impl CrashRound {
             },
             payout: self.payout,
             result: self.result.clone(),
+            commit: Some(self.commit.clone()),
+            seed: if self.is_running() {
+                None
+            } else {
+                Some(self.seed.clone())
+            },
         }
     }
 
@@ -146,6 +167,34 @@ pub struct CrashGame {
     uniforms: VecDeque<f64>,
 }
 
+/// Hex encode a round seed. Lowercase, no separators.
+fn seed_hex(seed: &[u8]) -> String {
+    let mut out = String::with_capacity(seed.len() * 2);
+    for byte in seed {
+        use std::fmt::Write as _;
+        let _ = write!(out, "{byte:02x}");
+    }
+    out
+}
+
+/// Draw a seed whose committed point matches a queued test uniform.
+///
+/// The first eight bytes are the big-endian integer closest to
+/// `uniform * 2^64`; the remaining bytes are zero. This keeps the existing
+/// deterministic crash-point tests meaningful while every round still has a
+/// real seed.
+fn seed_from_uniform(uniform: f64) -> [u8; SEED_LEN] {
+    let uniform = if uniform.is_finite() {
+        uniform.clamp(0.0, 0.999_999_999_999_999_9)
+    } else {
+        0.0
+    };
+    let value = (uniform * 18_446_744_073_709_551_616.0) as u64;
+    let mut seed = [0u8; SEED_LEN];
+    seed[..8].copy_from_slice(&value.to_be_bytes());
+    seed
+}
+
 impl CrashGame {
     pub fn new() -> Self {
         Self {
@@ -163,12 +212,25 @@ impl CrashGame {
         }
     }
 
+    /// Draw the next round seed. Tests supply uniforms; production uses the
+    /// operating system's random source.
+    pub fn next_seed(&mut self) -> [u8; SEED_LEN] {
+        if let Some(uniform) = self.uniforms.pop_front() {
+            return seed_from_uniform(uniform);
+        }
+        let mut seed = [0u8; SEED_LEN];
+        rand::thread_rng().fill_bytes(&mut seed);
+        seed
+    }
+
+    /// Kept for callers that only need the point a queued uniform encodes.
     pub fn next_crash_point(&mut self) -> f64 {
-        let uniform = self
-            .uniforms
-            .pop_front()
-            .unwrap_or_else(rand::random::<f64>);
-        crash_point_from_uniform(uniform)
+        crash_point_from_seed(&self.next_seed())
+    }
+
+    /// The uniform encoded by a seed, exposed for verification tests.
+    pub fn uniform_of(seed: &[u8; SEED_LEN]) -> f64 {
+        seed_to_uniform(seed)
     }
 }
 
diff --git a/src/version.rs b/src/version.rs
index c1dcee5..adc2a8d 100644
--- a/src/version.rs
+++ b/src/version.rs
@@ -5,6 +5,7 @@
 //! accepted until the server has answered it.
 
 use std::env;
+use std::time::{SystemTime, UNIX_EPOCH};
 
 /// Version this build reports. The client and the server share it.
 pub const VERSION: &str = env!("CARGO_PKG_VERSION");
@@ -73,9 +74,9 @@ pub fn is_newer(latest: &str, current: &str) -> bool {
     }
 }
 
-/// The server line that accepts a handshake.
-pub fn hello_line(version: &str, latest: &str, url: &str) -> String {
-    format!("HELLO {version} latest={latest} url={url}")
+/// The server line that accepts a handshake. `time` is Unix milliseconds.
+pub fn hello_line(version: &str, latest: &str, url: &str, time: u64) -> String {
+    format!("HELLO {version} latest={latest} url={url} time={time}")
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -83,9 +84,11 @@ pub struct HelloReply {
     pub version: String,
     pub latest: String,
     pub url: String,
+    /// Server clock at the moment the reply was built, Unix milliseconds.
+    pub time: u64,
 }
 
-/// Parse `HELLO <version> latest=<version> url=<url>`.
+/// Parse `HELLO <version> latest=<version> url=<url> time=<unix_ms>`.
 pub fn parse_hello(line: &str) -> Option<HelloReply> {
     let rest = line.trim().strip_prefix("HELLO ")?;
     let mut tokens = rest.split_whitespace();
@@ -93,11 +96,14 @@ pub fn parse_hello(line: &str) -> Option<HelloReply> {
 
     let mut latest = None;
     let mut url = None;
+    let mut time = None;
     for token in tokens {
         if let Some(value) = token.strip_prefix("latest=") {
             latest = Some(value.to_string());
         } else if let Some(value) = token.strip_prefix("url=") {
             url = Some(value.to_string());
+        } else if let Some(value) = token.strip_prefix("time=") {
+            time = value.parse().ok();
         }
     }
 
@@ -105,9 +111,29 @@ pub fn parse_hello(line: &str) -> Option<HelloReply> {
         version,
         latest: latest?,
         url: url?,
+        time: time?,
     })
 }
 
+/// The reply to `PING`: `PONG <unix_ms>`.
+pub fn pong_line(time: u64) -> String {
+    format!("PONG {time}")
+}
+
+/// Parse a `PONG` reply's server time.
+pub fn parse_pong(line: &str) -> Option<u64> {
+    line.trim().strip_prefix("PONG ")?.trim().parse().ok()
+}
+
+/// Current Unix time in milliseconds. Used for handshake timestamps and crash
+/// anchors; a system clock before the epoch reads as zero.
+pub fn unix_time_ms() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|duration| duration.as_millis().min(u128::from(u64::MAX)) as u64)
+        .unwrap_or(0)
+}
+
 /// Download page advertised by the server. `DOWNLOAD_URL` wins when set.
 pub fn download_url() -> String {
     env::var("DOWNLOAD_URL")
diff --git a/tests/client_core.rs b/tests/client_core.rs
index 2f43d47..3a2fb27 100644
--- a/tests/client_core.rs
+++ b/tests/client_core.rs
@@ -7,17 +7,17 @@
 use std::time::Duration;
 use zagan_bet::blackjack::BlackjackState;
 use zagan_bet::client::core::{ClientCore, Effect};
-use zagan_bet::client::input::{game_input, Editor, GameInput, Input, Key};
-use zagan_bet::client::shell::{self, Shell};
-use zagan_bet::client::ui::help_lines;
 use zagan_bet::client::games::response::{
     parse_blackjack_response, parse_crash_response, parse_spin_response,
 };
 use zagan_bet::client::games::roulette::{Cursor, Direction};
+use zagan_bet::client::input::{Editor, GameInput, Input, Key, game_input};
+use zagan_bet::client::shell::{self, Shell};
 use zagan_bet::client::ui::command_names;
+use zagan_bet::client::ui::help_lines;
 use zagan_bet::client::view::{Command, RoulettePhase, SlotsPhase, View};
-use zagan_bet::roulette::BetTarget;
 use zagan_bet::crash::{CrashState, multiplier_at};
+use zagan_bet::roulette::BetTarget;
 
 const WIN3: &str = "CCCCLLCLODGSDGS";
 const LOSS: &str = "CLOOGDSLCDCOGLS";
@@ -54,7 +54,7 @@ impl Screen {
                     self.region_start = None;
                     self.region_len = 0;
                 }
-                Effect::SendLine(line) => sent.push(line.clone()),
+                Effect::SendRequest { payload, .. } => sent.push(payload.clone()),
                 Effect::Quit | Effect::Disconnect => {}
             }
         }
@@ -601,7 +601,7 @@ fn ping_prints_pong() {
     h.line("ping");
     assert_eq!(h.sent.last().map(String::as_str), Some("PING"));
 
-    h.reply("PONG");
+    h.reply("PONG 1700000000000");
 
     assert!(h.screen.lines.iter().any(|line| line == "Pong"));
 }
@@ -968,6 +968,13 @@ fn crash_state(
         crash_point,
         payout,
         result: phase.to_string(),
+        started_at: 1_700_000_000_000,
+        commit: Some("00".repeat(32)),
+        seed: if phase == "running" {
+            None
+        } else {
+            Some("00".repeat(32))
+        },
     }
 }
 
@@ -1221,11 +1228,12 @@ fn history_prints_recent_plays() {
     let json = r#"[{"game":"roulette","bet":10,"winnings":20,"balance_after":1010,"at":"2026-10-30 01:20:11","details":{"number":"17","color":"black"}}]"#;
     h.reply(&format!("HISTORY {json}"));
 
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line.starts_with("Recent plays (1)")));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line.starts_with("Recent plays (1)"))
+    );
     let row = h
         .screen
         .lines
@@ -1242,11 +1250,12 @@ fn history_without_plays_says_so() {
     let mut h = Harness::new();
     h.line("history");
     h.reply("HISTORY []");
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line == "No plays recorded yet."));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line == "No plays recorded yet.")
+    );
 }
 
 #[test]
@@ -1254,11 +1263,12 @@ fn history_rejects_a_bad_count_without_sending() {
     let mut h = Harness::new();
     h.line("history 0");
     assert!(!h.sent.iter().any(|line| line == "HISTORY 0"));
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line.contains("Usage: history [1-50]")));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line.contains("Usage: history [1-50]"))
+    );
 }
 
 #[test]
@@ -1291,10 +1301,7 @@ fn the_roulette_view_reflects_the_cursor_and_bets() {
         Some(BetTarget::Straight { number: 2 })
     );
     assert_eq!(view.bets.total(), 10);
-    assert_eq!(
-        view.bets.amount_on(&BetTarget::Straight { number: 2 }),
-        10
-    );
+    assert_eq!(view.bets.amount_on(&BetTarget::Straight { number: 2 }), 10);
 }
 
 #[test]
@@ -1302,7 +1309,9 @@ fn clicking_a_bet_target_does_not_move_the_cursor() {
     let mut h = Harness::new();
     h.enter_roulette();
 
-    let effects = h.core.command(Command::PlaceBetAt(BetTarget::Split { a: 1, b: 4 }));
+    let effects = h
+        .core
+        .command(Command::PlaceBetAt(BetTarget::Split { a: 1, b: 4 }));
     h.apply(effects);
 
     let Some(View::Roulette(view)) = h.core.view() else {
@@ -1387,9 +1396,7 @@ fn the_slots_view_carries_the_result() {
     let mut h = Harness::new();
     h.enter_slots("10");
     h.key(Key::Char(' '));
-    h.reply(&format!(
-        "GAME_RESULT s1 20 10 1010 {WIN3} win 1 0,3,6"
-    ));
+    h.reply(&format!("GAME_RESULT s1 20 10 1010 {WIN3} win 1 0,3,6"));
 
     let Some(View::Slots(view)) = h.core.view() else {
         panic!("expected a slots view");
@@ -1518,11 +1525,12 @@ fn history_is_a_screen_and_keeps_its_records() {
     assert_eq!(view.records[0].summary(), "cashed 1.13x");
 
     // The terminal adapter still prints the table.
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line.starts_with("Recent plays (1)")));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line.starts_with("Recent plays (1)"))
+    );
 }
 
 #[test]
@@ -1563,11 +1571,12 @@ fn a_login_command_sends_auth_and_sets_the_user() {
     };
     assert_eq!(lobby.user.as_deref(), Some("alice"));
     assert!(lobby.login_error.is_none());
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line == "Logged in as alice"));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line == "Logged in as alice")
+    );
 }
 
 #[test]
@@ -1600,11 +1609,12 @@ fn a_register_command_sends_register_and_reports_the_result() {
     assert_eq!(h.sent.last().map(String::as_str), Some("REGISTER bob hash"));
 
     h.reply("REGISTERED bob");
-    assert!(h
-        .screen
-        .lines
-        .iter()
-        .any(|line| line == "Account created. Log in to play."));
+    assert!(
+        h.screen
+            .lines
+            .iter()
+            .any(|line| line == "Account created. Log in to play.")
+    );
 }
 
 #[test]
@@ -1646,3 +1656,56 @@ fn the_crash_multiplier_is_not_rounded_for_the_chart() {
         "a two-decimal store would flatten the curve into steps"
     );
 }
+
+#[test]
+fn a_reply_is_routed_by_request_id_and_late_replies_are_ignored() {
+    let mut h = Harness::new();
+    let first = h.core.command(Command::Ping);
+    let first_id = first
+        .iter()
+        .find_map(|effect| match effect {
+            Effect::SendRequest { id, .. } => Some(*id),
+            _ => None,
+        })
+        .unwrap();
+
+    let second = h.core.command(Command::Info);
+    let second_id = second
+        .iter()
+        .find_map(|effect| match effect {
+            Effect::SendRequest { id, .. } => Some(*id),
+            _ => None,
+        })
+        .unwrap();
+    assert_ne!(first_id, second_id, "ids must be unique on the connection");
+
+    // The ping reply arrives after INFO was sent. It must not complete INFO.
+    assert!(
+        h.core
+            .handle_reply_id(first_id, "PONG 1700000000000")
+            .is_empty()
+    );
+    let effects = h.core.handle_reply_id(second_id, "INFO alice 1 1000");
+    assert!(
+        effects.iter().any(|effect| matches!(effect, Effect::Print(lines) if lines.iter().any(|line| line.contains("Balance: 1000")))),
+        "the matching reply is applied"
+    );
+}
+
+#[test]
+fn a_crash_tick_updates_the_board_for_its_own_session() {
+    let mut h = Harness::new();
+    h.enter_crash();
+    h.key(Key::Char(' '));
+    let running = crash_state("running", 1.0, None, 0, 990);
+    h.reply(&crash_line("CRASH_START", &running));
+    assert!(h.board()[2].contains("Multiplier: 1.00x"));
+
+    h.push("crash.tick session=cr1 t=1700000000100 m=1.5");
+    assert!(h.board()[2].contains("Multiplier: 1.50x"));
+    assert!(h.board()[3].contains("Potential: 15 Kr"));
+
+    // A tick for another round cannot move this one.
+    h.push("crash.tick session=other t=1700000000200 m=9.0");
+    assert!(h.board()[2].contains("Multiplier: 1.50x"));
+}
diff --git a/tests/crash.rs b/tests/crash.rs
index 797874b..513f9c8 100644
--- a/tests/crash.rs
+++ b/tests/crash.rs
@@ -102,3 +102,42 @@ fn crash_points_are_clamped_to_the_liability_cap() {
     assert_eq!(crash_point_from_uniform(0.999_999), MAX_MULTIPLIER);
     assert_eq!(crash_point_from_uniform(1.0), MAX_MULTIPLIER);
 }
+
+#[test]
+fn a_seed_commits_to_its_crash_point_and_can_be_verified() {
+    use zagan_bet::crash::{
+        SEED_LEN, commit_seed, crash_point_from_seed, seed_from_hex, seed_to_uniform, verify_seed,
+    };
+
+    let mut seed = [0u8; SEED_LEN];
+    let value = (0.67_f64 * 18_446_744_073_709_551_616.0) as u64;
+    seed[..8].copy_from_slice(&value.to_be_bytes());
+    let commit = commit_seed(&seed);
+    let hex = format!(
+        "{}",
+        seed.iter()
+            .map(|byte| format!("{byte:02x}"))
+            .collect::<String>()
+    );
+
+    assert_eq!(seed_from_hex(&hex).as_deref(), Some(seed.as_slice()));
+    assert!(verify_seed(&hex, &commit));
+    assert!(!verify_seed(&hex, &"00".repeat(32)), "a wrong commit fails");
+    assert!(!verify_seed("nope", &commit), "bad hex fails");
+
+    // The point the client recomputes is the point the server committed to.
+    close(crash_point_from_seed(&seed), 3.0, 1e-9);
+    close(crash_point_from_seed(&seed), 3.0, 1e-9);
+
+    // The first eight bytes are the uniform; the rest are still hashed.
+    close(seed_to_uniform(&seed), 0.67, 1e-9);
+    let mut altered = seed;
+    altered[SEED_LEN - 1] = 1;
+    assert!(!verify_seed(
+        &altered
+            .iter()
+            .map(|byte| format!("{byte:02x}"))
+            .collect::<String>(),
+        &commit
+    ));
+}
diff --git a/tests/protocol.rs b/tests/protocol.rs
index bf8a4fd..d829ba9 100644
--- a/tests/protocol.rs
+++ b/tests/protocol.rs
@@ -1,84 +1,136 @@
-use std::io::{Cursor, Error, ErrorKind};
+use std::io::Cursor;
+use zagan_bet::protocol::{
+    FrameBuffer, FrameError, MAX_FRAME_LEN, Packet, encode_frame, event_line, io_failure_message,
+    parse_packet, parse_request, reply_line, request_line,
+};
 
-use zagan_bet::protocol::{io_failure_message, LineBuffer};
+fn framed(payload: &str) -> Vec<u8> {
+    encode_frame(payload)
+}
 
 #[test]
-fn keeps_data_after_the_first_newline() {
-    let mut buffer = LineBuffer::new();
-    buffer.push(b"PONG\nGAME_RESULT session 60 10 990 OSS two\n");
+fn decodes_every_complete_frame_and_keeps_the_remainder() {
+    let mut buffer = FrameBuffer::new();
+    let mut bytes = framed("RES 1 PONG 1700000000000");
+    bytes.extend(framed("EVT 2 crash.tick session=cr1 t=1700000000100 m=1.5"));
+    buffer.push(&bytes);
 
-    assert_eq!(buffer.next_line().as_deref(), Some("PONG"));
     assert_eq!(
-        buffer.next_line().as_deref(),
-        Some("GAME_RESULT session 60 10 990 OSS two")
+        buffer.next_frame().unwrap().unwrap(),
+        "RES 1 PONG 1700000000000"
+    );
+    assert_eq!(
+        buffer.next_frame().unwrap().unwrap(),
+        "EVT 2 crash.tick session=cr1 t=1700000000100 m=1.5"
     );
-    assert_eq!(buffer.next_line(), None);
+    assert!(buffer.next_frame().is_none());
+    assert!(buffer.is_empty());
 }
 
 #[test]
-fn handles_crlf_and_empty_lines() {
-    let mut buffer = LineBuffer::new();
-    buffer.push(b"PONG\r\n\r\n");
+fn waits_for_a_partial_frame() {
+    let mut buffer = FrameBuffer::new();
+    let bytes = framed("RES 7 OK");
+    buffer.push(&bytes[..3]);
+    assert!(buffer.next_frame().is_none());
 
-    assert_eq!(buffer.next_line().as_deref(), Some("PONG"));
-    assert_eq!(buffer.next_line().as_deref(), Some(""));
-    assert_eq!(buffer.next_line(), None);
+    buffer.push(&bytes[3..7]);
+    assert!(buffer.next_frame().is_none());
+
+    buffer.push(&bytes[7..]);
+    assert_eq!(buffer.next_frame().unwrap().unwrap(), "RES 7 OK");
 }
 
 #[test]
-fn waits_for_a_split_line() {
-    let mut buffer = LineBuffer::new();
-    buffer.push(b"PO");
-    assert_eq!(buffer.next_line(), None);
+fn an_oversized_length_is_rejected_without_waiting_for_bytes() {
+    let mut buffer = FrameBuffer::new();
+    buffer.push(&((MAX_FRAME_LEN as u32 + 1).to_be_bytes()));
+    match buffer.next_frame() {
+        Some(Err(FrameError::TooLarge(length))) => {
+            assert_eq!(length, MAX_FRAME_LEN + 1);
+        }
+        other => panic!("expected an oversize error, got {other:?}"),
+    }
+    assert!(buffer.is_empty(), "the buffer must not keep the bad frame");
+}
 
-    buffer.push(b"NG\n");
-    assert_eq!(buffer.next_line().as_deref(), Some("PONG"));
+#[test]
+fn invalid_utf8_is_a_protocol_error() {
+    let mut buffer = FrameBuffer::new();
+    buffer.push(&1u32.to_be_bytes());
+    buffer.push(&[0xff]);
+    assert_eq!(buffer.next_frame(), Some(Err(FrameError::InvalidUtf8)));
 }
 
 #[test]
-fn reads_multiple_lines_from_a_reader() {
-    let mut buffer = LineBuffer::new();
-    let mut reader = Cursor::new(b"one\ntwo\n".to_vec());
+fn reads_frames_from_a_blocking_reader() {
+    let mut bytes = framed("RES 1 OK");
+    bytes.extend(framed("EVT 1 crash.tick session=cr1 t=1 m=1.0"));
+    let mut reader = Cursor::new(bytes);
+    let mut buffer = FrameBuffer::new();
 
     assert_eq!(
-        buffer.read_line(&mut reader).unwrap().as_deref(),
-        Some("one")
+        buffer.read_frame(&mut reader).unwrap().as_deref(),
+        Some("RES 1 OK")
     );
     assert_eq!(
-        buffer.read_line(&mut reader).unwrap().as_deref(),
-        Some("two")
+        buffer.read_frame(&mut reader).unwrap().as_deref(),
+        Some("EVT 1 crash.tick session=cr1 t=1 m=1.0")
     );
-    assert_eq!(buffer.read_line(&mut reader).unwrap(), None);
+    assert_eq!(buffer.read_frame(&mut reader).unwrap(), None);
 }
 
 #[test]
-fn returns_a_partial_line_at_eof() {
-    let mut buffer = LineBuffer::new();
-    let mut reader = Cursor::new(b"partial".to_vec());
-
+fn builds_and_parses_the_envelope() {
     assert_eq!(
-        buffer.read_line(&mut reader).unwrap().as_deref(),
-        Some("partial")
+        request_line(42, None, "PLAY_START crash 50"),
+        "REQ 42 PLAY_START crash 50"
     );
-    assert_eq!(buffer.read_line(&mut reader).unwrap(), None);
+    assert_eq!(
+        request_line(42, Some("abc123"), "PLAY_START crash 50"),
+        "REQ 42 idem=abc123 PLAY_START crash 50"
+    );
+
+    let request = parse_request("REQ 42 idem=abc123 PLAY_START crash 50").unwrap();
+    assert_eq!(request.id, 42);
+    assert_eq!(request.idem.as_deref(), Some("abc123"));
+    assert_eq!(request.payload, "PLAY_START crash 50");
+
+    let request = parse_request("REQ 7 PING").unwrap();
+    assert_eq!(request.id, 7);
+    assert_eq!(request.idem, None);
+    assert_eq!(request.payload, "PING");
+
+    assert!(parse_request("PLAY_START crash 50").is_err());
+    assert!(parse_request("REQ nope PING").is_err());
+    assert!(parse_request("REQ 1 idem= PING").is_err());
 }
 
 #[test]
-fn timeout_errors_get_a_timeout_message() {
-    assert_eq!(
-        io_failure_message(&Error::from(ErrorKind::TimedOut)),
-        "ERROR Request timed out"
-    );
-    assert_eq!(
-        io_failure_message(&Error::from(ErrorKind::WouldBlock)),
-        "ERROR Request timed out"
-    );
+fn parses_replies_and_events() {
     assert_eq!(
-        io_failure_message(&Error::from(ErrorKind::UnexpectedEof)),
-        "ERROR Connection lost"
+        parse_packet(&reply_line(9, "ERROR Insufficient balance")).unwrap(),
+        Packet::Reply {
+            id: 9,
+            body: "ERROR Insufficient balance".to_string()
+        }
     );
     assert_eq!(
-        io_failure_message(&Error::from(ErrorKind::ConnectionReset)),
-        "ERROR Connection lost"
+        parse_packet(&event_line(3, "CRASH_BUSTED {}")).unwrap(),
+        Packet::Event {
+            seq: 3,
+            body: "CRASH_BUSTED {}".to_string()
+        }
     );
+    assert!(parse_packet("REQ 1 PING").is_err());
+    assert!(parse_packet("RES nope OK").is_err());
+}
+
+#[test]
+fn io_failures_are_reported_as_short_messages() {
+    let timeout = std::io::Error::new(std::io::ErrorKind::TimedOut, "slow");
+    assert_eq!(io_failure_message(&timeout), "ERROR Request timed out");
+
+    let closed = std::io::Error::new(std::io::ErrorKind::UnexpectedEof, "gone");
+    assert_eq!(io_failure_message(&closed), "ERROR Connection lost");
 }
diff --git a/tests/server_core.rs b/tests/server_core.rs
index e2600e4..6c9c835 100644
--- a/tests/server_core.rs
+++ b/tests/server_core.rs
@@ -101,11 +101,11 @@ fn crash_state(response: &str) -> CrashState {
 }
 
 fn hello(core: &mut ServerCore, state: &mut ConnectionState) {
-    let response = core.handle_message(
-        state,
-        &format!("HELLO {}", zagan_bet::version::VERSION),
+    let response = core.handle_message(state, &format!("HELLO {}", zagan_bet::version::VERSION));
+    assert!(
+        response.starts_with("HELLO "),
+        "handshake failed: {response}"
     );
-    assert!(response.starts_with("HELLO "), "handshake failed: {response}");
 }
 
 fn register(core: &mut ServerCore, state: &mut ConnectionState, user: &str) {
@@ -258,8 +258,18 @@ fn roulette_settles_split_bets_and_records_details() {
 
     let mut bets = Bets::default();
     bets.add(BetTarget::Outside { kind: Outside::Red }, 10);
-    bets.add(BetTarget::Outside { kind: Outside::Black }, 10);
-    bets.add(BetTarget::Outside { kind: Outside::Even }, 10);
+    bets.add(
+        BetTarget::Outside {
+            kind: Outside::Black,
+        },
+        10,
+    );
+    bets.add(
+        BetTarget::Outside {
+            kind: Outside::Even,
+        },
+        10,
+    );
     bets.add(BetTarget::Outside { kind: Outside::Odd }, 10);
     bets.add(BetTarget::Straight { number: 17 }, 5);
     let bets = bets.to_json();
@@ -671,10 +681,14 @@ fn crash_poll_pushes_the_bust_exactly_once() {
     let started = crash_state(&core.handle_message(&mut state, "PLAY_START crash 10"));
 
     clock.advance(1.0);
+    let ticks = core.poll(&state);
+    assert_eq!(ticks.len(), 1, "a running round pushes coalesced ticks");
     assert!(
-        core.poll(&state).is_empty(),
-        "a running round must not push anything"
+        ticks[0].starts_with("crash.tick session="),
+        "tick: {}",
+        ticks[0]
     );
+    assert!(ticks[0].contains(" m="), "tick carries the multiplier");
 
     clock.advance(15.0);
     let pushed = core.poll(&state);
@@ -920,9 +934,10 @@ fn history_lists_recent_plays_newest_first() {
     login(&mut core, &mut state, "alice");
 
     for _ in 0..3 {
-        assert!(core
-            .handle_message(&mut state, "PLAY_START slots 10")
-            .starts_with("GAME_RESULT"));
+        assert!(
+            core.handle_message(&mut state, "PLAY_START slots 10")
+                .starts_with("GAME_RESULT")
+        );
     }
 
     let response = core.handle_message(&mut state, "HISTORY 2");
@@ -979,7 +994,10 @@ fn hello_reports_the_version_and_download_url() {
     assert!(state.greeted());
 
     // The gate is open now.
-    assert_eq!(core.handle_message(&mut state, "PING"), "PONG");
+    assert!(
+        core.handle_message(&mut state, "PING").starts_with("PONG "),
+        "PING must carry the server time"
+    );
 }
 
 #[test]
@@ -999,7 +1017,10 @@ fn hello_refuses_a_different_major_or_minor() {
             response.starts_with("ERROR Version mismatch"),
             "response: {response}"
         );
-        assert!(!state.greeted(), "a refused handshake must not open the gate");
+        assert!(
+            !state.greeted(),
+            "a refused handshake must not open the gate"
+        );
         assert_eq!(
             core.handle_message(&mut state, "PING"),
             "ERROR HELLO required"
@@ -1014,9 +1035,10 @@ fn hello_accepts_a_patch_difference_and_rejects_bad_input() {
     let patch = format!("{}.{}.{}", server.major, server.minor, server.patch + 1);
 
     let mut state = ConnectionState::default();
-    assert!(core
-        .handle_message(&mut state, &format!("HELLO {patch}"))
-        .starts_with("HELLO "));
+    assert!(
+        core.handle_message(&mut state, &format!("HELLO {patch}"))
+            .starts_with("HELLO ")
+    );
 
     let mut other = ConnectionState::default();
     assert_eq!(
@@ -1028,3 +1050,70 @@ fn hello_accepts_a_patch_difference_and_rejects_bad_input() {
         "ERROR Invalid version"
     );
 }
+
+#[test]
+fn crash_start_commits_to_a_seed_and_the_end_reveals_it() {
+    use zagan_bet::crash::{crash_point_from_seed, seed_from_hex, verify_seed};
+
+    let (mut core, _path, clock) = setup_crash("crash-commit", CRASH_AT_3);
+    let mut state = ConnectionState::default();
+    register(&mut core, &mut state, "alice");
+    login(&mut core, &mut state, "alice");
+
+    let started = crash_state(&core.handle_message(&mut state, "PLAY_START crash 10"));
+    let commit = started.commit.clone().expect("a start reply commits");
+    assert_eq!(commit.len(), 64, "sha256 hex");
+    assert_eq!(started.seed, None, "the seed stays hidden while running");
+    assert_eq!(started.crash_point, None);
+    assert!(started.started_at > 1_600_000_000_000, "server time anchor");
+
+    clock.advance(5.0);
+    let cashed = crash_state(
+        &core.handle_message(&mut state, &format!("CRASH_CASHOUT {}", started.session_id)),
+    );
+    let seed = cashed.seed.clone().expect("the end reveals the seed");
+    assert!(verify_seed(&seed, &commit), "the reveal matches the commit");
+    let bytes = seed_from_hex(&seed).expect("32-byte hex seed");
+    let point = crash_point_from_seed(&bytes);
+    assert!(
+        (point - cashed.crash_point.unwrap()).abs() < 1e-9,
+        "the client recomputes the same point"
+    );
+    assert_eq!(cashed.commit.as_deref(), Some(commit.as_str()));
+}
+
+#[test]
+fn a_repeated_request_id_replays_its_reply_without_charging_twice() {
+    use zagan_bet::protocol::Request;
+
+    let (mut core, _path) = setup("idempotent-spin", WIN3);
+    let mut state = ConnectionState::default();
+    register(&mut core, &mut state, "alice");
+    login(&mut core, &mut state, "alice");
+
+    let request = Request {
+        id: 41,
+        idem: Some("spin-1".to_string()),
+        payload: "PLAY_START slots 10".to_string(),
+    };
+    let first = core.handle_request(&mut state, &request);
+    assert!(first.starts_with("GAME_RESULT"), "first: {first}");
+    assert_eq!(core.balance("alice"), Some(1000));
+    assert_eq!(core.play_count("alice"), 1);
+
+    let replay = core.handle_request(&mut state, &request);
+    assert_eq!(replay, first, "the cached reply is returned verbatim");
+    assert_eq!(core.balance("alice"), Some(1000), "no second debit");
+    assert_eq!(core.play_count("alice"), 1, "no second audit row");
+
+    let different = Request {
+        id: 41,
+        idem: Some("spin-2".to_string()),
+        payload: "PLAY_START slots 20".to_string(),
+    };
+    assert_eq!(
+        core.handle_request(&mut state, &different),
+        "ERROR Request id reused with a different command"
+    );
+    assert_eq!(core.balance("alice"), Some(1000));
+}
diff --git a/tests/version.rs b/tests/version.rs
index af244db..31bc2b6 100644
--- a/tests/version.rs
+++ b/tests/version.rs
@@ -1,5 +1,6 @@
 use zagan_bet::version::{
-    compatible, hello_line, is_newer, parse_hello, Version, VERSION,
+    VERSION, Version, compatible, hello_line, is_newer, parse_hello, parse_pong, pong_line,
+    unix_time_ms,
 };
 
 #[test]
@@ -24,16 +25,16 @@ fn versions_parse_and_reject_nonsense() {
         Version::parse("4.0.0-rc1").map(|v| (v.major, v.minor, v.patch)),
         Some((4, 0, 0))
     );
-    assert_eq!(
-        Version::parse("4.0.0+build7").map(|v| v.patch),
-        Some(0)
-    );
+    assert_eq!(Version::parse("4.0.0+build7").map(|v| v.patch), Some(0));
 
     for bad in ["", "4", "4.0", "4.0.0.1", "x.0.0", "4.x.0", "4.0.0-"] {
         assert!(Version::parse(bad).is_none(), "{bad:?} should not parse");
     }
 
-    assert!(Version::parse(VERSION).is_some(), "the build version must parse");
+    assert!(
+        Version::parse(VERSION).is_some(),
+        "the build version must parse"
+    );
 }
 
 #[test]
@@ -57,19 +58,45 @@ fn newer_versions_are_ordered_by_major_minor_patch() {
 
 #[test]
 fn the_hello_reply_round_trips() {
-    let line = hello_line("4.0.0", "4.1.2", "https://zagan.example/");
+    let line = hello_line(
+        "4.0.0",
+        "4.1.2",
+        "https://zagan.example/",
+        1_700_000_000_123,
+    );
     let reply = parse_hello(&line).expect("parse a generated reply");
 
     assert_eq!(reply.version, "4.0.0");
     assert_eq!(reply.latest, "4.1.2");
     assert_eq!(reply.url, "https://zagan.example/");
+    assert_eq!(reply.time, 1_700_000_000_123);
 
-    assert!(parse_hello("HELLO 4.0.0 url=https://x/").is_none(), "latest is required");
-    assert!(parse_hello("HELLO 4.0.0 latest=4.0.0").is_none(), "url is required");
+    assert!(
+        parse_hello("HELLO 4.0.0 url=https://x/ time=1").is_none(),
+        "latest is required"
+    );
+    assert!(
+        parse_hello("HELLO 4.0.0 latest=4.0.0 time=1").is_none(),
+        "url is required"
+    );
+    assert!(
+        parse_hello("HELLO 4.0.0 latest=4.0.0 url=https://x/").is_none(),
+        "time is required"
+    );
     assert!(parse_hello("PONG").is_none());
     assert!(parse_hello("HELLO").is_none());
 }
 
+#[test]
+fn pong_carries_the_server_time() {
+    let line = pong_line(1_700_000_000_456);
+    assert_eq!(line, "PONG 1700000000456");
+    assert_eq!(parse_pong(&line), Some(1_700_000_000_456));
+    assert!(parse_pong("PONG").is_none());
+    assert!(parse_pong("RES 1 PONG 1700000000456").is_none());
+    assert!(unix_time_ms() > 1_600_000_000_000);
+}
+
 /// The GUI is a client, so it must ship in lockstep with the TUI and server.
 /// Keep `gui/Cargo.toml` at the same version as the root package.
 #[test]
@@ -83,6 +110,18 @@ fn the_gui_member_uses_the_same_version() {
     assert_eq!(gui_version, VERSION);
 }
 
+/// The gateway is a frontend too; keep it in lockstep with the core.
+#[test]
+fn the_webd_member_uses_the_same_version() {
+    let manifest = include_str!("../webd/Cargo.toml");
+    let version = manifest
+        .lines()
+        .find_map(|line| line.trim().strip_prefix("version = "))
+        .expect("webd/Cargo.toml declares a version")
+        .trim_matches('"');
+    assert_eq!(version, VERSION);
+}
+
 /// egui's dependency tree must never enter the TUI or server build graph.
 /// The GUI is a workspace member that depends on this package, never the
 /// other way round.
diff --git a/tests/web_types.rs b/tests/web_types.rs
new file mode 100644
index 0000000..21af474
--- /dev/null
+++ b/tests/web_types.rs
@@ -0,0 +1,138 @@
+//! The browser and gateway exchange serde JSON for `Command`/`View`. These
+//! tests pin the wire shape the TypeScript app renders.
+
+use zagan_bet::client::games::roulette::{Cursor, Direction};
+use zagan_bet::client::view::{
+    BlackjackView, Command, CrashView, HistoryView, LobbyView, RoulettePhase, RouletteView,
+    SlotsPhase, SlotsView, View,
+};
+use zagan_bet::roulette::{BetTarget, Bets, Outside};
+
+#[test]
+fn browser_commands_deserialize() {
+    let login: Command =
+        serde_json::from_str(r#"{"Login":{"user":"alice","credential":"abc"}}"#).unwrap();
+    assert_eq!(
+        login,
+        Command::Login {
+            user: "alice".to_string(),
+            credential: "abc".to_string()
+        }
+    );
+
+    let play: Command = serde_json::from_str(r#"{"Play":{"game":"crash","bet":25}}"#).unwrap();
+    assert_eq!(
+        play,
+        Command::Play {
+            game: "crash".to_string(),
+            bet: Some(25)
+        }
+    );
+
+    let bet: Command =
+        serde_json::from_str(r#"{"PlaceBetAt":{"bet":"outside","kind":"red"}}"#).unwrap();
+    assert_eq!(
+        bet,
+        Command::PlaceBetAt(BetTarget::Outside { kind: Outside::Red })
+    );
+
+    let split: Command =
+        serde_json::from_str(r#"{"PlaceBetAt":{"bet":"split","a":1,"b":2}}"#).unwrap();
+    assert_eq!(split, Command::PlaceBetAt(BetTarget::Split { a: 1, b: 2 }));
+
+    assert_eq!(
+        serde_json::from_str::<Command>(r#""Spin""#).unwrap(),
+        Command::Spin
+    );
+    assert_eq!(
+        serde_json::from_str::<Command>(r#""ShowLobby""#).unwrap(),
+        Command::ShowLobby
+    );
+    assert_eq!(
+        serde_json::from_str::<Command>(r#"{"SetBet":50}"#).unwrap(),
+        Command::SetBet(50)
+    );
+    assert_eq!(
+        serde_json::from_str::<Command>(r#"{"MoveCursor":"Left"}"#).unwrap(),
+        Command::MoveCursor(Direction::Left)
+    );
+}
+
+#[test]
+fn views_serialize_with_a_screen_tag() {
+    let lobby = View::Lobby(LobbyView {
+        connected: true,
+        user: Some("alice".to_string()),
+        account: Some("1".to_string()),
+        balance: Some(1000),
+        games: vec![("slots".to_string(), "Slots".to_string())],
+        login_error: None,
+    });
+    let json = serde_json::to_value(&lobby).unwrap();
+    assert_eq!(json["screen"], "lobby");
+    assert_eq!(json["user"], "alice");
+
+    let slots = View::Slots(SlotsView {
+        bet: 10,
+        balance: Some(990),
+        reels: "CLOGD".chars().collect(),
+        win_cells: vec![0],
+        win_lines: vec![1],
+        win_type: "win".to_string(),
+        winnings: Some(20),
+        phase: SlotsPhase::Result,
+        error: None,
+    });
+    let json = serde_json::to_value(&slots).unwrap();
+    assert_eq!(json["screen"], "slots");
+    assert_eq!(json["phase"], "result");
+    assert_eq!(json["reels"][0], "C");
+
+    let roulette = View::Roulette(RouletteView {
+        bet_amount: 10,
+        balance: Some(1000),
+        chip: 25,
+        bets: Bets::default(),
+        cursor: Cursor::default(),
+        phase: RoulettePhase::Placing,
+        number: None,
+        color: None,
+        winnings: None,
+        error: None,
+    });
+    let json = serde_json::to_value(&roulette).unwrap();
+    assert_eq!(json["screen"], "roulette");
+    assert_eq!(json["phase"], "placing");
+
+    let blackjack = View::Blackjack(BlackjackView {
+        status: "ready".to_string(),
+        balance: Some(1000),
+        bet: 10,
+        hand: None,
+        error: None,
+    });
+    assert_eq!(
+        serde_json::to_value(&blackjack).unwrap()["screen"],
+        "blackjack"
+    );
+
+    let crash = View::Crash(CrashView {
+        status: "running".to_string(),
+        balance: Some(990),
+        bet: 10,
+        multiplier: 1.5,
+        potential: 15,
+        crash_point: None,
+        payout: 0,
+        started_at: 1_700_000_000_000,
+        commit: Some("ab".repeat(32)),
+        seed: None,
+        error: None,
+    });
+    let json = serde_json::to_value(&crash).unwrap();
+    assert_eq!(json["screen"], "crash");
+    assert_eq!(json["commit"], "ab".repeat(32));
+
+    let history = View::History(HistoryView { records: vec![] });
+    assert_eq!(serde_json::to_value(&history).unwrap()["screen"], "history");
+}
diff --git a/web/README.md b/web/README.md
index 81346fd..3e81468 100644
--- a/web/README.md
+++ b/web/README.md
@@ -13,6 +13,7 @@ web/
   releases.php   shared scanner and hash cache
   install.sh     stable Linux installer
   install.ps1    stable Windows installer
+  play/          browser app, served at /play/
   bin/gui/       apps, served at /bin/gui/...
   bin/client/    terminal clients
   bin/server/    servers
@@ -20,6 +21,26 @@ web/
 
 Serve `web/` as the document root. Binaries in `bin/` are gitignored.
 
+## Browser app
+
+`play/` is a static vanilla TypeScript app. It talks to the WebSocket gateway
+in `webd/`, not to the game server: the browser sends `Command` JSON and renders
+`View` JSON, and the gateway owns the upstream TLS connection and the pinned
+server key. nginx serves `/play/` and proxies `/ws` to `127.0.0.1:8890`.
+
+Build it before publishing:
+
+```sh
+cd web/play
+npm ci
+npm run build      # writes app.js
+cd ../..
+```
+
+Commit the generated `app.js`; the site then needs no Node at deploy time.
+`npm run typecheck` checks the sources. The gateway has its own deployment
+notes in `webd/README.md`; it is not part of the player download.
+
 ## Naming
 
 The page only lists files that match the release pattern; anything else in
@@ -132,9 +153,9 @@ Then open <http://127.0.0.1:8899/>.
 `deploy.sh` rsyncs `web/` with `--delay-updates`, so a visitor never sees a
 half-written binary, then fetches the live page and every artifact it lists —
 GUI apps, installers, terminal clients and servers — and compares the
-downloaded bytes with the local SHA-256. `--verify-only` skips the
-upload and only checks the live site. Old versions are left on the server;
-prune them by hand.
+downloaded bytes with the local SHA-256. It also fetches `/play/`, `app.js` and
+`style.css`. `--verify-only` skips the upload and only checks the live site.
+Old versions are left on the server; prune them by hand.
 
 A local directory works as a target, which is how the verification itself is
 tested:
diff --git a/web/index.php b/web/index.php
index 3f0ab92..b03eac6 100644
--- a/web/index.php
+++ b/web/index.php
@@ -58,6 +58,7 @@ function human_size(int $bytes): string
 <body>
 
 <h1>żagań.bet</h1>
+<p><a href="<?= e($base) ?>/play/"><strong>Play in your browser</strong></a> — no install, just an account. Play-money only.</p>
 <p>Official desktop app, terminal client and server builds.</p>
 <?php if ($newest > 0): ?>
 <p>Builds published <?= e(gmdate('j M Y H:i', $newest)) ?> UTC.</p>
diff --git a/web/nginx.conf.example b/web/nginx.conf.example
index 9fc942f..d440ab5 100644
--- a/web/nginx.conf.example
+++ b/web/nginx.conf.example
@@ -37,6 +37,31 @@ server {
         add_header Cache-Control "public, max-age=31536000, immutable";
     }
 
+    # The browser app: static files, no framework runtime.
+    location = /play {
+        return 301 /play/;
+    }
+
+    location /play/ {
+        try_files $uri $uri/ /play/index.html;
+        add_header Cache-Control "no-cache";
+        add_header X-Frame-Options "DENY" always;
+        add_header X-Content-Type-Options "nosniff" always;
+    }
+
+    # WebSocket gateway. Keep the upgrade headers and a long read timeout:
+    # a crash round can idle for a while between pushes.
+    location = /ws {
+        proxy_pass http://127.0.0.1:8890;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_set_header Host $host;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_read_timeout 3600s;
+        proxy_send_timeout 3600s;
+    }
+
     # The page rescans bin/ on every request, so don't cache it.
     location = /index.php {
         include fastcgi_params;
diff --git a/web/play/.gitignore b/web/play/.gitignore
new file mode 100644
index 0000000..63738f6
--- /dev/null
+++ b/web/play/.gitignore
@@ -0,0 +1,2 @@
+node_modules/
+app.js.map
diff --git a/web/play/README.md b/web/play/README.md
new file mode 100644
index 0000000..610c7a8
--- /dev/null
+++ b/web/play/README.md
@@ -0,0 +1,56 @@
+# `web/play` — browser frontend
+
+Vanilla TypeScript + esbuild. The browser sends `Command` JSON and renders
+`View` JSON; it contains no game rules, no payout math and no wire protocol.
+The gateway in `webd/` owns the upstream TLS connection.
+
+## Build
+
+```sh
+npm ci
+npm run build      # writes app.js
+npm run typecheck
+npm test           # headless DOM smoke test (jsdom)
+```
+
+Commit the generated `app.js` so the site deploys without Node.
+
+## Local development
+
+Serve the repository's `web/` directory (for `/play/`) and put the gateway
+behind the same origin at `/ws`. The simplest local setup is nginx with the
+`web/nginx.conf.example` block pointed at a staging root and
+`ZAGAN_WEB_ORIGIN=http://127.0.0.1:8899`. For the app alone:
+
+```sh
+python3 -m http.server 8900 -d web/play
+```
+
+It will load, but the WebSocket will only connect through nginx or another
+proxy that routes `/ws` to `webd`.
+
+## Screens
+
+- Auth: login/register. The password is hashed with Web Crypto (`SHA-256`)
+  before it leaves the page; the gateway and browser never store it.
+- Lobby: four games, per-game bet, history.
+- Slots: five reels, win cells and paylines.
+- Roulette: canvas felt with straight, dozen, column and outside chips;
+  left click adds, right click removes.
+- Blackjack: dealer/player cards, hit/stand/double/forfeit.
+- Crash: curve, live multiplier, cash-out, commit/seed verification.
+- History: settled plays with net result.
+
+## Theme
+
+`style.css` mirrors the palette in `gui/src/theme.rs`: near-black ground,
+cyan focus, green for wins, gold for chips, felt green only for roulette.
+Do not introduce a second palette or hard-code colours in the render modules.
+
+## Security
+
+- The session cookie is HttpOnly and SameSite=Strict; JavaScript never reads
+  it and never stores a credential.
+- Notices are inserted with `textContent`, not HTML.
+- The app is play-money only. Do not add deposits, withdrawals, KYC or
+  real-money claims without a product decision and an ADR.
diff --git a/web/play/app.js b/web/play/app.js
new file mode 100644
index 0000000..3320693
--- /dev/null
+++ b/web/play/app.js
@@ -0,0 +1 @@
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The total is reserved when you spin.")),n.append(o("div","label","Chip"));let u=o("div","chip-row");for(let l of[10,25,50,100,500]){let c=o("button",`chip-btn ${Number(t.chip)===l?"active":""}`,String(l));c.disabled=a,c.addEventListener("click",()=>s({SetChip:l})),u.append(c)}n.append(u);let g=(t.bets?.chips??[]).reduce((l,c)=>l+Number(c.amount??0),0),h=o("div","stat");if(h.append(o("span","muted","On the felt"),o("strong","mono",L(g))),n.append(h),t.balance!==null&&t.balance!==void 0){let l=o("div","stat");l.append(o("span","muted","Balance"),o("strong","mono",L(Number(t.balance)))),n.append(l)}t.error&&n.append(o("p","error-text",String(t.error)));let v=o("p","note");if(a)v.textContent="Spinning…";else if(t.phase==="result"){let l=Number(t.winnings??0);v.textContent=`${t.number} ${t.color} · ${l>0?`won ${L(l)}`:"no win"}`,v.className=l>0?"note win-text":"note"}else v.textContent=g>0?"Ready to spin.":"Place at least one chip.";n.append(v);let y=o("div","actions"),w=o("button","btn primary wide big",a?"SPINNING…":"SPIN WHEEL");w.disabled=a||g===0,w.addEventListener("click",()=>s("Spin"));let E=o("button","btn wide","Clear bets");E.disabled=a||g===0,E.addEventListener("click",()=>s("ClearBets"));let S=o("button","btn ghost wide","Leave table");S.disabled=a,S.addEventListener("click",()=>{a||s("Leave")}),y.append(w,E,S),n.append(y)}var Q=5,ee=3,D="CLOGDS",rt=["top","middle","bottom","V","inverted V"],oe=0,I,te=null,ne=null;function at(){oe=Date.now()+900}function it(e){return e.phase==="spinning"||Date.now()<oe}function se(e,n,t,s){te=t,ne=e,I!==void 0&&(window.clearInterval(I),I=void 0);let a=it(t);H(e),H(n);let r=o("h2",void 0,"Slots"),d=o("p","note","Match three or more symbols from the left. 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Cash out before it crashes."},yt=location.pathname.includes("/play/")?location.pathname.slice(0,location.pathname.indexOf("/play/")):"",kt=`${location.protocol==="https:"?"wss":"ws"}://${location.host}${yt}/ws`,Z=new j(kt,{onHello(e){De=e.time-Date.now(),$=e.user??null,$e.textContent=`v${e.version}`},onView(e){x=e,typeof e.balance=="number"&&(ce=e.balance),e.screen==="lobby"&&"user"in e&&($=e.user??null,$?U.value="":ce=null),ie=0,K.hidden=!0,Fe(),$&&x.balance===null&&ae!==$&&(ae=$,Z.send("Info")),$||(ae=null)},onNotice(e){e.startsWith("Connected to:")||e.startsWith("Fingerprint:")||e.startsWith("User:")||e.startsWith("Account:")||e.startsWith("Balance:")||(J(e,he(e)),e.startsWith("Account created")&&(de("login"),U.value="",Ae.focus()),A.disabled=!1,A.textContent=_==="login"?"Log in":"Create account")},onError(e){J(e,"bad"),A.disabled=!1,A.textContent=_==="login"?"Log in":"Create account"},onReplaced(){Re.hidden=!1},onPong(){},onOpen(){K.hidden=!0},onClosed(e){if(Re.hidden!==!1){if(!e){Be.textContent="The connection could not be restored. Reload the page to try again.",K.hidden=!1;return}ie+=1,Be.textContent=ie>1?"Still trying to reach the game server…":"Trying to reach the game server…",K.hidden=!1}}});function B(e){Z.send(e)}function Lt(){return Date.now()+De}function de(e){_=e,Pe.classList.toggle("active",e==="login"),We.classList.toggle("active",e==="register"),A.textContent=e==="login"?"Log in":"Create account",U.autocomplete=e==="login"?"current-password":"new-password",F.textContent=""}function V(e){lt.hidden=e!=="auth",ct.hidden=e!=="lobby",dt.hidden=e!=="game",ut.hidden=e!=="history"}function xt(e){mt.textContent=L(e??null)}function Fe(){if(!x)return;let e=$;if(e?(He.hidden=!1,pt.textContent=String(e)):He.hidden=!0,xt(ce),!e){V("auth"),F.textContent=x.login_error?String(x.login_error):"",x.screen==="lobby"&&x.connected===!1&&(F.textContent="The game server is not reachable yet. 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Continue?")||B("Leave")});k("reload-replaced").addEventListener("click",()=>location.reload());k("reload-reconnect").addEventListener("click",()=>location.reload());window.addEventListener("resize",()=>{window.clearTimeout(window.__resizeTimer),window.__resizeTimer=window.setTimeout(()=>{x&&Fe()},140)});window.setInterval(()=>{$&&Z.ping()},25e3);Z.connect();})();
diff --git a/web/play/build.mjs b/web/play/build.mjs
new file mode 100644
index 0000000..40af074
--- /dev/null
+++ b/web/play/build.mjs
@@ -0,0 +1,22 @@
+import { build, context } from "esbuild";
+
+const watch = process.argv.includes("--watch");
+
+const options = {
+  entryPoints: ["src/main.ts"],
+  bundle: true,
+  outfile: "app.js",
+  format: "iife",
+  target: ["es2020"],
+  minify: !watch,
+  sourcemap: watch ? "inline" : false,
+  charset: "utf8",
+  logLevel: "info",
+};
+
+if (watch) {
+  const ctx = await context(options);
+  await ctx.watch();
+} else {
+  await build(options);
+}
diff --git a/web/play/index.html b/web/play/index.html
new file mode 100644
index 0000000..e9d4b79
--- /dev/null
+++ b/web/play/index.html
@@ -0,0 +1,112 @@
+<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>Play — żagań.bet</title>
+<meta name="description" content="Play slots, roulette, blackjack and crash with play credits. No real money.">
+<meta name="color-scheme" content="dark">
+<meta http-equiv="Content-Security-Policy" content="default-src 'none'; script-src 'self'; style-src 'self' 'unsafe-inline'; connect-src 'self' ws: wss:; img-src 'self' data:; base-uri 'none'; form-action 'self'">
+<link rel="stylesheet" href="style.css">
+</head>
+<body>
+<div class="shell">
+  <header class="topbar">
+    <a class="brand" href="/">żagań<span>.bet</span></a>
+    <span class="tagline">Play credits · no real money</span>
+    <span class="spacer"></span>
+    <div id="session-bar" class="session" hidden>
+      <span class="who">Signed in as <strong id="account-name"></strong></span>
+      <span id="account-balance" class="balance">— Kr</span>
+      <button id="logout" class="btn ghost small" type="button">Log out</button>
+    </div>
+  </header>
+
+  <main>
+    <section id="auth-screen" hidden>
+      <div class="auth-wrap">
+        <div class="auth-card">
+          <h1>Play żagań.bet</h1>
+          <p class="muted" style="margin: 6px 0 20px">Play-money casino. Your balance is play credit; nothing here is real money.</p>
+          <div class="auth-tabs" role="tablist">
+            <button id="tab-login" class="auth-tab active" type="button" role="tab">Log in</button>
+            <button id="tab-register" class="auth-tab" type="button" role="tab">Register</button>
+          </div>
+          <form id="auth-form">
+            <label class="field">
+              <span class="label">Username</span>
+              <input id="auth-user" class="input" type="text" autocomplete="username" maxlength="32" required>
+            </label>
+            <label class="field">
+              <span class="label">Password</span>
+              <input id="auth-pass" class="input" type="password" autocomplete="current-password" required>
+            </label>
+            <p id="auth-error" class="error-text" style="margin: 0; min-height: 18px"></p>
+            <button id="auth-submit" class="btn primary wide big" type="submit">Log in</button>
+          </form>
+          <p class="auth-foot">Registration gives you 1 000 Kr of play credit. No deposits, no withdrawals, no personal data beyond a username.</p>
+        </div>
+      </div>
+    </section>
+
+    <section id="lobby-screen" hidden>
+      <div class="lobby-head">
+        <div>
+          <h1>Lobby</h1>
+          <p class="muted" style="margin: 4px 0 0">Choose a game. Bets are play credits.</p>
+        </div>
+        <span class="spacer"></span>
+        <button id="show-history" class="btn ghost" type="button">Play history</button>
+        <button id="refresh-lobby" class="btn ghost" type="button">Refresh</button>
+      </div>
+      <div id="game-grid" class="game-grid"></div>
+    </section>
+
+    <section id="game-screen" hidden>
+      <div class="game-head">
+        <button id="leave-game" class="btn ghost" type="button">← Lobby</button>
+        <h1 id="game-title">Game</h1>
+        <span class="spacer"></span>
+        <span id="game-badge" class="label"></span>
+      </div>
+      <div class="game-body">
+        <div id="game-board" class="board"></div>
+        <aside id="game-side" class="sidebar"></aside>
+      </div>
+    </section>
+
+    <section id="history-screen" hidden>
+      <div class="lobby-head">
+        <div>
+          <h1>Play history</h1>
+          <p class="muted" style="margin: 4px 0 0">The last plays on your account.</p>
+        </div>
+        <span class="spacer"></span>
+        <button id="history-back" class="btn ghost" type="button">← Lobby</button>
+      </div>
+      <div id="history-body"></div>
+    </section>
+  </main>
+</div>
+
+<div id="toasts" aria-live="polite"></div>
+
+<div id="replaced-overlay" class="overlay" hidden>
+  <div class="modal">
+    <h2>Opened in another tab</h2>
+    <p>This game was opened somewhere else. Only one tab can play a session at a time.</p>
+    <button id="reload-replaced" class="btn primary" type="button">Reload this tab</button>
+  </div>
+</div>
+
+<div id="reconnect-overlay" class="overlay" hidden>
+  <div class="modal">
+    <h2>Connection lost</h2>
+    <p id="reconnect-message">Trying to reach the game server…</p>
+    <button id="reload-reconnect" class="btn ghost" type="button">Reload</button>
+  </div>
+</div>
+
+<script src="app.js" defer></script>
+</body>
+</html>
diff --git a/web/play/package-lock.json b/web/play/package-lock.json
new file mode 100644
index 0000000..831527f
--- /dev/null
+++ b/web/play/package-lock.json
@@ -0,0 +1,1031 @@
+{
+  "name": "zagan-bet-play",
+  "version": "5.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "zagan-bet-play",
+      "version": "5.0.0",
+      "devDependencies": {
+        "esbuild": "^0.28.0",
+        "jsdom": "^30.1.3",
+        "typescript": "^5.9.0"
+      }
+    },
+    "node_modules/@asamuzakjp/css-color": {
+      "version": "7.1.9",
+      "resolved": "https://registry.npmjs.org/@asamuzakjp/css-color/-/css-color-7.1.9.tgz",
+      "integrity": "sha512-vZ6JQVq8Ivgz6b/IBlAf90wZviXdluY13cQOPO+nJHbmXwGrPl2GcpqUY7a55/8ZVdfONXpCFMpRijOBCHNlcQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@csstools/css-calc": "^3.4.3",
+        "@csstools/css-color-parser": "^4.2.6",
+        "@csstools/css-parser-algorithms": "^4.0.2",
+        "@csstools/css-tokenizer": "^4.0.2",
+        "lru-cache": "^11.5.3"
+      },
+      "engines": {
+        "node": "^22.22.2 || ^24.15.0 || >=26.0.0"
+      }
+    },
+    "node_modules/@asamuzakjp/dom-selector": {
+      "version": "10.0.5",
+      "resolved": "https://registry.npmjs.org/@asamuzakjp/dom-selector/-/dom-selector-10.0.5.tgz",
+      "integrity": "sha512-EgmJ7oEaGQECTn3H3wmnQpEy4hKY66VvM7VQndwPIQob3p877BgbyOUE3EX0LgXQCciF2H8KMdR+RznqjMNOLw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "bidi-js": "^1.1.0",
+        "css-tree": "^3.2.1",
+        "is-potential-custom-element-name": "^1.0.1",
+        "lru-cache": "^11.5.3"
+      },
+      "engines": {
+        "node": "^22.22.2 || ^24.15.0 || >=26.0.0"
+      }
+    },
+    "node_modules/@bramus/specificity": {
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diff --git a/web/play/package.json b/web/play/package.json
new file mode 100644
index 0000000..3e3cebf
--- /dev/null
+++ b/web/play/package.json
@@ -0,0 +1,20 @@
+{
+  "name": "zagan-bet-play",
+  "private": true,
+  "version": "5.0.0",
+  "type": "module",
+  "scripts": {
+    "build": "node build.mjs",
+    "watch": "node build.mjs --watch",
+    "typecheck": "tsc --noEmit",
+    "test": "node test/smoke.mjs"
+  },
+  "devDependencies": {
+    "esbuild": "^0.28.0",
+    "jsdom": "^30.1.3",
+    "typescript": "^5.9.0"
+  },
+  "engines": {
+    "node": ">=20"
+  }
+}
diff --git a/web/play/src/blackjack.ts b/web/play/src/blackjack.ts
new file mode 100644
index 0000000..3537f45
--- /dev/null
+++ b/web/play/src/blackjack.ts
@@ -0,0 +1,152 @@
+import type { View } from "./types";
+import { cardFace, clear, money, node } from "./dom";
+
+function cardElement(card: string): HTMLElement {
+  if (card === "?") {
+    const back = node("div", "card back");
+    back.append(node("span", "rank", "?"), node("span", "suit", ""));
+    return back;
+  }
+  const face = cardFace(card);
+  const element = node("div", "card");
+  if (face.red) element.classList.add("red");
+  element.append(node("span", "rank", face.rank), node("span", "suit", face.suit));
+  return element;
+}
+
+function handBlock(label: string, cards: string[], total: number): HTMLElement {
+  const block = node("div", "hand");
+  block.append(node("div", "label", label));
+  const row = node("div", "cards");
+  for (const card of cards) row.append(cardElement(card));
+  const sum = node("div", "total");
+  sum.append(document.createTextNode("Total "), node("strong", undefined, String(total)));
+  block.append(row, sum);
+  return block;
+}
+
+function outcome(view: View, hand: any): string {
+  const result = String(hand?.result ?? "");
+  const winnings = Number(hand?.winnings ?? 0);
+  switch (result) {
+    case "blackjack":
+      return `Blackjack — won ${money(winnings)}`;
+    case "win":
+      return `You win — ${money(winnings)}`;
+    case "push":
+      return `Push — ${money(winnings)} returned`;
+    case "bust":
+      return "Bust — the bet is lost";
+    case "lose":
+      return "Dealer wins — the bet is lost";
+    case "forfeit":
+      return "Hand forfeited — the bet is lost";
+    case "playing":
+      return view.status === "player" ? "Your move." : "Dealing…";
+    default:
+      return "Ready to deal.";
+  }
+}
+
+export function renderBlackjack(
+  board: HTMLElement,
+  side: HTMLElement,
+  view: View,
+  send: (command: unknown) => void,
+): void {
+  clear(board);
+  clear(side);
+
+  const hand = view.hand;
+  const playerPhase = hand?.phase === "player" || view.status === "player";
+  const done = hand?.phase === "done" || view.status === "done";
+  const canDeal = !hand || done;
+
+  board.append(node("h2", undefined, "Blackjack"));
+  board.append(
+    node("p", "note", "Six decks. Dealer stands on all 17. Blackjack pays 3:2."),
+  );
+
+  if (hand) {
+    board.append(handBlock("Dealer", hand.dealer ?? [], Number(hand.dealer_total ?? 0)));
+    board.append(handBlock("You", hand.player ?? [], Number(hand.player_total ?? 0)));
+  } else {
+    const empty = node("div", "outcome");
+    empty.textContent = "Press DEAL to start a hand.";
+    board.append(empty);
+  }
+
+  if (done || (hand && !playerPhase)) {
+    const result = node("div", "outcome");
+    result.textContent = outcome(view, hand);
+    if (String(hand?.result) === "win" || String(hand?.result) === "blackjack" || String(hand?.result) === "push") {
+      result.classList.add("win-text");
+    }
+    board.append(result);
+  }
+
+  if (view.error) board.append(node("p", "error-text", String(view.error)));
+
+  // Sidebar
+  side.append(node("div", "label", "Blackjack"));
+  const bet = Number(hand?.bet ?? view.bet ?? 0);
+  const balance = view.balance ?? view.hand?.balance;
+  side.append(node("p", "note", "Hit, stand or double. Forfeiting loses the reserved bet."));
+
+  if (canDeal) {
+    const betRow = node("div", "row");
+    const minus = node("button", "btn small", "−10");
+    const amount = node("strong", "mono", money(bet));
+    const plus = node("button", "btn small", "+10");
+    minus.addEventListener("click", () => send({ AdjustBet: -10 }));
+    plus.addEventListener("click", () => send({ AdjustBet: 10 }));
+    betRow.append(minus, amount, plus);
+    side.append(node("div", "label", "Bet"), betRow);
+  } else {
+    const stat = node("div", "stat");
+    stat.append(node("span", "muted", "Bet"), node("strong", undefined, money(bet)));
+    side.append(stat);
+  }
+
+  if (balance !== undefined) {
+    const stat = node("div", "stat");
+    stat.append(node("span", "muted", "Balance"), node("strong", undefined, money(Number(balance))));
+    side.append(stat);
+  }
+
+  const actions = node("div", "actions");
+  if (playerPhase) {
+    const actionsRow = node("div", "row wrap");
+    for (const action of hand?.actions ?? []) {
+      const label = action === "hit" ? "HIT" : action === "stand" ? "STAND" : "DOUBLE";
+      const button =
+        action === "stand"
+          ? node("button", "btn primary", label)
+          : node("button", "btn", label);
+      button.addEventListener("click", () => {
+        if (action === "hit") send("Hit");
+        else if (action === "stand") send("Stand");
+        else send("Double");
+      });
+      actionsRow.append(button);
+    }
+    actions.append(actionsRow);
+    const forfeit = node("button", "btn danger wide", "Forfeit hand");
+    forfeit.addEventListener("click", () => {
+      if (window.confirm("Forfeit this hand? The reserved bet is lost.")) send("Forfeit");
+    });
+    actions.append(forfeit);
+  } else if (canDeal) {
+    const deal = node("button", "btn primary wide big", "DEAL");
+    deal.addEventListener("click", () => send("Deal"));
+    actions.append(deal);
+  }
+
+  const leave = node("button", "btn ghost wide", playerPhase ? "Leave (forfeits)" : "Leave table");
+  leave.addEventListener("click", () => {
+    if (playerPhase && !window.confirm("Leaving forfeits this hand. Continue?")) return;
+    send("Leave");
+  });
+  actions.append(leave);
+  side.append(actions);
+}
diff --git a/web/play/src/crash.ts b/web/play/src/crash.ts
new file mode 100644
index 0000000..6f3c8dd
--- /dev/null
+++ b/web/play/src/crash.ts
@@ -0,0 +1,365 @@
+import type { View } from "./types";
+import { clear, money, node, shortHash } from "./dom";
+
+const GROWTH = Math.LN2 / 5;
+
+type Clock = { now: () => number };
+
+type Parts = {
+  board: HTMLElement;
+  side: HTMLElement;
+  number: HTMLElement;
+  meta: HTMLElement;
+  verify: HTMLElement;
+  canvas: HTMLCanvasElement;
+  bet: HTMLElement;
+  potential: HTMLElement;
+  balance: HTMLElement;
+  status: HTMLElement;
+  lastCrash: HTMLElement;
+  error: HTMLElement;
+  primary: HTMLButtonElement;
+  leave: HTMLButtonElement;
+  minus: HTMLButtonElement;
+  plus: HTMLButtonElement;
+};
+
+let parts: Parts | null = null;
+let current: View | null = null;
+let clock: Clock | null = null;
+let sendCommand: ((command: unknown) => void) | null = null;
+let frameHandle: number | undefined;
+let verifyToken = 0;
+let lastStatus = "";
+
+function build(
+  board: HTMLElement,
+  side: HTMLElement,
+  send: (command: unknown) => void,
+  now: Clock,
+): Parts {
+  clear(board);
+  clear(side);
+  sendCommand = send;
+  clock = now;
+
+  board.append(node("h2", undefined, "Crash"));
+  board.append(
+    node("p", "note", "The multiplier rises from 1.00×. Cash out before it crashes."),
+  );
+
+  const wrap = node("div", "crash-wrap");
+  const number = node("div", "crash-number", "1.00×");
+  const meta = node("div", "crash-meta");
+  const canvas = node("canvas", "crash-canvas") as HTMLCanvasElement;
+  const verify = node("div", "verify", "Waiting for a round commitment.");
+  wrap.append(number, meta, canvas, verify);
+  board.append(wrap);
+
+  side.append(node("div", "label", "Crash"));
+  side.append(node("p", "note", "The server commits to a seed before the round. The seed is revealed when it ends."));
+
+  const betRow = node("div", "row");
+  const minus = node("button", "btn small", "−10") as HTMLButtonElement;
+  const bet = node("strong", "mono", "—");
+  const plus = node("button", "btn small", "+10") as HTMLButtonElement;
+  minus.addEventListener("click", () => sendCommand?.({ AdjustBet: -10 }));
+  plus.addEventListener("click", () => sendCommand?.({ AdjustBet: 10 }));
+  betRow.append(minus, bet, plus);
+  side.append(node("div", "label", "Bet"), betRow);
+
+  const potential = node("strong", "mono", "—");
+  const balance = node("strong", "mono", "—");
+  for (const [label, value] of [
+    ["Potential", potential],
+    ["Balance", balance],
+  ] as const) {
+    const row = node("div", "stat");
+    row.append(node("span", "muted", label), value);
+    side.append(row);
+  }
+
+  const status = node("p", "note", "Ready.");
+  const lastCrash = node("p", "note", "");
+  const error = node("p", "error-text");
+  side.append(status, lastCrash, error);
+
+  const actions = node("div", "actions");
+  const primary = node("button", "btn primary wide big", "START") as HTMLButtonElement;
+  const leave = node("button", "btn ghost wide", "Leave table") as HTMLButtonElement;
+  primary.addEventListener("click", () => {
+    if (current?.status === "running") sendCommand?.("CashOut");
+    else sendCommand?.("Start");
+  });
+  leave.addEventListener("click", () => {
+    if (current?.status === "running" && !window.confirm("Forfeit this round? The bet is lost.")) return;
+    sendCommand?.("Leave");
+  });
+  actions.append(primary, leave);
+  side.append(actions);
+
+  return {
+    board,
+    side,
+    number,
+    meta,
+    verify,
+    canvas,
+    bet,
+    potential,
+    balance,
+    status,
+    lastCrash,
+    error,
+    primary,
+    leave,
+    minus,
+    plus,
+  };
+}
+
+export function renderCrash(
+  board: HTMLElement,
+  side: HTMLElement,
+  view: View,
+  send: (command: unknown) => void,
+  now: Clock,
+): void {
+  if (!parts || parts.board !== board) {
+    parts = build(board, side, send, now);
+    lastStatus = "";
+  }
+  const p = parts;
+  sendCommand = send;
+  clock = now;
+  current = view;
+
+  if (view.status !== lastStatus) {
+    if (view.status === "starting" || view.status === "running") {
+      if (lastStatus !== "running") {
+        p.verify.className = "verify";
+        p.verify.textContent = "Round committed; seed hidden until the round ends.";
+      }
+    }
+    lastStatus = String(view.status);
+  }
+
+  const running = view.status === "running";
+  const starting = view.status === "starting";
+  const live = running || starting;
+
+  p.bet.textContent = money(Number(view.bet ?? 0));
+  p.potential.textContent = money(Number(view.potential ?? view.bet ?? 0));
+  p.balance.textContent = view.balance === null || view.balance === undefined ? "—" : money(Number(view.balance));
+  p.error.textContent = view.error ? String(view.error) : "";
+
+  p.minus.disabled = live;
+  p.plus.disabled = live;
+  p.primary.textContent = running ? "CASH OUT" : starting ? "STARTING…" : "START";
+  p.primary.disabled = starting;
+  p.primary.className = running ? "btn primary wide big" : "btn primary wide big";
+  p.leave.textContent = running ? "Forfeit round" : "Leave table";
+
+  if (running) {
+    p.status.textContent = "Rising — cash out before the crash.";
+    p.status.className = "note win-text";
+  } else if (starting) {
+    p.status.textContent = "Starting the round…";
+    p.status.className = "note";
+  } else if (view.status === "cashed") {
+    p.status.textContent = `Cashed out at ${Number(view.multiplier ?? 0).toFixed(2)}× for ${money(Number(view.payout ?? 0))}.`;
+    p.status.className = "note win-text";
+  } else if (view.status === "crashed") {
+    p.status.textContent = `Crashed at ${Number(view.crash_point ?? view.multiplier ?? 0).toFixed(2)}×. The bet is lost.`;
+    p.status.className = "note error-text";
+  } else if (view.status === "forfeit") {
+    p.status.textContent = "Round forfeited.";
+    p.status.className = "note error-text";
+  } else {
+    p.status.textContent = "Ready. Start a round when you want.";
+    p.status.className = "note";
+  }
+
+  if (view.crash_point !== null && view.crash_point !== undefined && view.status === "crashed") {
+    p.lastCrash.textContent = `Last crash: ${Number(view.crash_point).toFixed(2)}×`;
+  }
+
+  const commit = view.commit ? String(view.commit) : "";
+  p.meta.textContent = commit ? `commit ${shortHash(commit, 12)}` : "no commitment yet";
+
+  if (view.seed && commit) {
+    const token = ++verifyToken;
+    const seed = String(view.seed);
+    const crashPoint = Number(view.crash_point ?? 0);
+    void verifyReveal(seed, commit, crashPoint).then(([commitOk, pointOk]) => {
+      if (token !== verifyToken || !parts) return;
+      const ok = commitOk && pointOk;
+      parts.verify.className = `verify ${ok ? "ok" : "bad"}`;
+      parts.verify.textContent = ok
+        ? `Seed ${shortHash(seed, 12)} · sha256 matches commit · crash point recomputed`
+        : `VERIFICATION FAILED · seed ${shortHash(seed, 12)} · commit ${shortHash(commit, 12)}`;
+    });
+  } else if (!live && !commit) {
+    p.verify.className = "verify";
+    p.verify.textContent = "Waiting for a round commitment.";
+  }
+
+  if (frameHandle !== undefined) {
+    cancelAnimationFrame(frameHandle);
+    frameHandle = undefined;
+  }
+  if (running) {
+    const loop = () => {
+      if (!parts || current?.status !== "running") {
+        frameHandle = undefined;
+        return;
+      }
+      update(parts, current, now);
+      frameHandle = requestAnimationFrame(loop);
+    };
+    frameHandle = requestAnimationFrame(loop);
+  } else {
+    update(p, view, now);
+  }
+}
+
+function currentMultiplier(view: View, now: Clock): number {
+  if (view.status === "running") {
+    const elapsed = Math.max(0, (now.now() - Number(view.started_at ?? 0)) / 1000);
+    const local = Math.min(1000, Math.exp(GROWTH * elapsed));
+    return Math.max(local, Number(view.multiplier ?? 1));
+  }
+  if (view.status === "cashed") return Number(view.multiplier ?? 1);
+  if (view.status === "crashed") return Number(view.crash_point ?? view.multiplier ?? 1);
+  return 1;
+}
+
+function update(p: Parts, view: View, now: Clock): void {
+  const multiplier = currentMultiplier(view, now);
+  p.number.textContent = `${multiplier.toFixed(2)}×`;
+  p.number.className = `crash-number ${
+    view.status === "running"
+      ? "running"
+      : view.status === "cashed"
+        ? "cashed"
+        : view.status === "crashed"
+          ? "crashed"
+          : ""
+  }`;
+  p.potential.textContent = money(Math.floor(Number(view.bet ?? 0) * multiplier));
+  drawChart(p.canvas, view, multiplier, now);
+}
+
+function drawChart(canvas: HTMLCanvasElement, view: View, multiplier: number, now: Clock): void {
+  const width = canvas.clientWidth || 600;
+  const height = canvas.clientHeight || 360;
+  const dpr = window.devicePixelRatio || 1;
+  if (canvas.width !== Math.round(width * dpr) || canvas.height !== Math.round(height * dpr)) {
+    canvas.width = Math.round(width * dpr);
+    canvas.height = Math.round(height * dpr);
+  }
+  const ctx = canvas.getContext("2d");
+  if (!ctx) return;
+  ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
+  ctx.clearRect(0, 0, width, height);
+
+  const padL = 54;
+  const padR = 16;
+  const padT = 18;
+  const padB = 34;
+  const plotW = Math.max(1, width - padL - padR);
+  const plotH = Math.max(1, height - padT - padB);
+
+  const elapsed =
+    view.status === "running"
+      ? Math.max(0.25, (now.now() - Number(view.started_at ?? 0)) / 1000)
+      : multiplier > 1
+        ? Math.log(multiplier) / GROWTH
+        : 1;
+  const xMax = Math.max(5, elapsed * 1.08);
+  const yMax = Math.max(2, Math.ceil(multiplier * 1.15 * 2) / 2);
+  const x = (seconds: number) => padL + (seconds / xMax) * plotW;
+  const y = (value: number) => padT + plotH - ((value - 1) / (yMax - 1)) * plotH;
+
+  ctx.strokeStyle = "#242e38";
+  ctx.fillStyle = "#8a98a6";
+  ctx.font = "11px ui-monospace, monospace";
+  ctx.lineWidth = 1;
+  for (let step = 0; step <= 4; step += 1) {
+    const value = 1 + ((yMax - 1) * step) / 4;
+    const py = y(value);
+    ctx.beginPath();
+    ctx.moveTo(padL, py);
+    ctx.lineTo(width - padR, py);
+    ctx.stroke();
+    ctx.fillText(`${value.toFixed(1)}×`, 6, py + 4);
+  }
+  for (let step = 0; step <= 4; step += 1) {
+    const seconds = (xMax * step) / 4;
+    const px = x(seconds);
+    ctx.beginPath();
+    ctx.moveTo(px, padT);
+    ctx.lineTo(px, padT + plotH);
+    ctx.strokeStyle = "#1b232c";
+    ctx.stroke();
+    ctx.fillStyle = "#5b6773";
+    ctx.fillText(`${seconds.toFixed(0)}s`, px - 10, height - 12);
+  }
+
+  const line =
+    view.status === "crashed"
+      ? "#e05a5a"
+      : view.status === "cashed"
+        ? "#4ec27b"
+        : "#e0b64a";
+
+  ctx.beginPath();
+  const samples = 180;
+  for (let index = 0; index <= samples; index += 1) {
+    const seconds = (elapsed * index) / samples;
+    const value = Math.min(yMax, Math.exp(GROWTH * seconds));
+    const px = x(seconds);
+    const py = y(value);
+    if (index === 0) ctx.moveTo(px, py);
+    else ctx.lineTo(px, py);
+  }
+  ctx.strokeStyle = line;
+  ctx.lineWidth = 2.4;
+  ctx.stroke();
+
+  const endX = x(elapsed);
+  const endY = y(Math.min(yMax, multiplier));
+  ctx.beginPath();
+  ctx.arc(endX, endY, 4.5, 0, Math.PI * 2);
+  ctx.fillStyle = line;
+  ctx.fill();
+
+  ctx.fillStyle = line;
+  ctx.font = "600 12px ui-monospace, monospace";
+  ctx.fillText(`${multiplier.toFixed(2)}×`, Math.min(endX + 8, width - 70), Math.max(padT + 12, endY - 10));
+}
+
+async function verifyReveal(
+  seed: string,
+  commit: string,
+  crashPoint: number,
+): Promise<[boolean, boolean]> {
+  const bytes = new Uint8Array(seed.length / 2);
+  for (let index = 0; index < bytes.length; index += 1) {
+    bytes[index] = Number.parseInt(seed.slice(index * 2, index * 2 + 2), 16);
+  }
+  const digest = await crypto.subtle.digest("SHA-256", bytes);
+  const actual = [...new Uint8Array(digest)]
+    .map((byte) => byte.toString(16).padStart(2, "0"))
+    .join("");
+  const commitOk = actual === commit.toLowerCase();
+
+  let uniform = 0;
+  for (let index = 0; index < 8; index += 1) {
+    uniform = uniform * 256 + bytes[index];
+  }
+  uniform /= 2 ** 64;
+  const point = Math.max(1, Math.min(1000, (1 - 0.01) / (1 - uniform)));
+  const pointOk = Math.abs(point - crashPoint) < 1e-6;
+  return [commitOk, pointOk];
+}
diff --git a/web/play/src/dom.ts b/web/play/src/dom.ts
new file mode 100644
index 0000000..d8ed212
--- /dev/null
+++ b/web/play/src/dom.ts
@@ -0,0 +1,104 @@
+export function byId<T extends HTMLElement = HTMLElement>(id: string): T {
+  const node = document.getElementById(id);
+  if (!node) throw new Error(`missing #${id}`);
+  return node as T;
+}
+
+export function node<K extends keyof HTMLElementTagNameMap>(
+  tag: K,
+  className?: string,
+  text?: string,
+): HTMLElementTagNameMap[K] {
+  const element = document.createElement(tag);
+  if (className) element.className = className;
+  if (text !== undefined) element.textContent = text;
+  return element;
+}
+
+export function clear(element: HTMLElement): void {
+  element.replaceChildren();
+}
+
+export function groupDigits(amount: number): string {
+  const negative = amount < 0;
+  const digits = String(Math.abs(Math.trunc(amount)));
+  let grouped = "";
+  for (let index = 0; index < digits.length; index += 1) {
+    if (index > 0 && (digits.length - index) % 3 === 0) grouped += "\u2009";
+    grouped += digits[index];
+  }
+  return negative ? `-${grouped}` : grouped;
+}
+
+export function money(amount: number | null | undefined): string {
+  if (amount === null || amount === undefined || Number.isNaN(amount)) return "— Kr";
+  return `${groupDigits(amount)} Kr`;
+}
+
+export function signedMoney(amount: number): string {
+  return `${amount < 0 ? "-" : "+"}${money(Math.abs(amount))}`;
+}
+
+export function toast(text: string, tone: "info" | "good" | "bad" = "info"): void {
+  const root = document.getElementById("toasts");
+  if (!root || !text) return;
+  const item = node("div", `toast ${tone}`, text);
+  root.append(item);
+  window.setTimeout(() => {
+    item.style.opacity = "0";
+    item.style.transition = "opacity 220ms ease";
+    window.setTimeout(() => item.remove(), 240);
+  }, 4200);
+  while (root.children.length > 4) root.firstElementChild?.remove();
+}
+
+export function toneFor(text: string): "info" | "good" | "bad" {
+  const lowered = text.toLowerCase();
+  if (
+    text.startsWith("ERROR") ||
+    lowered.includes("failed") ||
+    lowered.includes("lost") ||
+    lowered.includes("invalid") ||
+    lowered.includes("forfeit")
+  ) {
+    return "bad";
+  }
+  if (
+    text.startsWith("Logged in") ||
+    text.startsWith("Account created") ||
+    lowered.includes("won") ||
+    lowered.includes("cashed")
+  ) {
+    return "good";
+  }
+  return "info";
+}
+
+export async function sha256Hex(text: string): Promise<string> {
+  const bytes = new TextEncoder().encode(text);
+  const digest = await crypto.subtle.digest("SHA-256", bytes);
+  return [...new Uint8Array(digest)]
+    .map((byte) => byte.toString(16).padStart(2, "0"))
+    .join("");
+}
+
+export function shortHash(hash: string, keep = 10): string {
+  if (hash.length <= keep * 2) return hash;
+  return `${hash.slice(0, keep)}…${hash.slice(-keep)}`;
+}
+
+export function formatTime(raw: string): string {
+  // SQLite stores `YYYY-MM-DD HH:MM:SS` in UTC.
+  const parsed = Date.parse(raw.includes("T") ? raw : raw.replace(" ", "T") + "Z");
+  if (Number.isNaN(parsed)) return raw;
+  return new Date(parsed).toLocaleString();
+}
+
+export function cardFace(card: string): { rank: string; suit: string; red: boolean } {
+  if (card === "?" || !card) return { rank: "?", suit: "", red: false };
+  const suit = card.slice(-1);
+  const rank = card.slice(0, -1);
+  const glyph =
+    suit === "C" ? "♣" : suit === "D" ? "♦" : suit === "H" ? "♥" : suit === "S" ? "♠" : suit;
+  return { rank, suit: glyph, red: suit === "D" || suit === "H" };
+}
diff --git a/web/play/src/history.ts b/web/play/src/history.ts
new file mode 100644
index 0000000..9e7a564
--- /dev/null
+++ b/web/play/src/history.ts
@@ -0,0 +1,60 @@
+import type { View } from "./types";
+import { clear, formatTime, money, node, signedMoney } from "./dom";
+
+function summary(record: any): string {
+  const details = record.details ?? {};
+  switch (record.game) {
+    case "slots":
+      return String(details.win_type ?? "spin");
+    case "roulette":
+      return `${details.number ?? "?"} ${details.color ?? ""}`.trim();
+    case "blackjack":
+      return String(details.result ?? "");
+    case "crash": {
+      const result = String(details.result ?? "");
+      const point = details.crash_point;
+      return point === undefined || point === null ? result : `${result} @ ${Number(point).toFixed(2)}×`;
+    }
+    default:
+      return "";
+  }
+}
+
+export function renderHistory(root: HTMLElement, view: View): void {
+  clear(root);
+  const records: any[] = view.records ?? [];
+  if (records.length === 0) {
+    const empty = node("div", "board");
+    empty.append(
+      node("h2", undefined, "No plays yet"),
+      node("p", "muted", "Your settled plays will appear here."),
+    );
+    root.append(empty);
+    return;
+  }
+
+  const wrap = node("div", "table-wrap");
+  const table = node("table");
+  const head = node("thead");
+  const headRow = node("tr");
+  for (const label of ["Time", "Game", "Bet", "Result", "Net", "Balance"]) {
+    headRow.append(node("th", undefined, label));
+  }
+  head.append(headRow);
+  const body = node("tbody");
+  for (const record of records) {
+    const row = node("tr");
+    row.append(node("td", "mono", formatTime(String(record.at ?? ""))));
+    row.append(node("td", undefined, String(record.game ?? "")));
+    row.append(node("td", "num", money(Number(record.bet ?? 0))));
+    row.append(node("td", "muted", summary(record)));
+    const net = Number(record.winnings ?? 0) - Number(record.bet ?? 0);
+    const netCell = node("td", `num ${net > 0 ? "pos" : net < 0 ? "neg" : ""}`, net === 0 ? "0 Kr" : signedMoney(net));
+    row.append(netCell);
+    row.append(node("td", "num", money(Number(record.balance_after ?? 0))));
+    body.append(row);
+  }
+  table.append(head, body);
+  wrap.append(table);
+  root.append(wrap);
+}
diff --git a/web/play/src/main.ts b/web/play/src/main.ts
new file mode 100644
index 0000000..fd55250
--- /dev/null
+++ b/web/play/src/main.ts
@@ -0,0 +1,323 @@
+import { byId, money, node, sha256Hex, toast, toneFor } from "./dom";
+import { Gateway } from "./net";
+import { renderBlackjack } from "./blackjack";
+import { renderCrash } from "./crash";
+import { renderHistory } from "./history";
+import { renderRoulette } from "./roulette";
+import { renderSlots } from "./slots";
+import type { View } from "./types";
+
+const authScreen = byId("auth-screen");
+const lobbyScreen = byId("lobby-screen");
+const gameScreen = byId("game-screen");
+const historyScreen = byId("history-screen");
+const sessionBar = byId("session-bar");
+const accountName = byId("account-name");
+const accountBalance = byId("account-balance");
+const gameGrid = byId("game-grid");
+const gameBoard = byId("game-board");
+const gameSide = byId("game-side");
+const gameTitle = byId("game-title");
+const gameBadge = byId("game-badge");
+const historyBody = byId("history-body");
+const authForm = byId<HTMLFormElement>("auth-form");
+const authUser = byId<HTMLInputElement>("auth-user");
+const authPass = byId<HTMLInputElement>("auth-pass");
+const authError = byId("auth-error");
+const authSubmit = byId<HTMLButtonElement>("auth-submit");
+const tabLogin = byId<HTMLButtonElement>("tab-login");
+const tabRegister = byId<HTMLButtonElement>("tab-register");
+const reconnectOverlay = byId("reconnect-overlay");
+const reconnectMessage = byId("reconnect-message");
+const replacedOverlay = byId("replaced-overlay");
+
+let view: View | null = null;
+let currentUser: string | null = null;
+let lastBalance: number | null = null;
+let authMode: "login" | "register" = "login";
+let infoFor: string | null = null;
+let serverOffset = 0;
+let reconnectAttempts = 0;
+const bets = new Map<string, number>([
+  ["slots", 10],
+  ["roulette", 10],
+  ["blackjack", 10],
+  ["crash", 10],
+]);
+
+const titles: Record<string, string> = {
+  slots: "Slots",
+  roulette: "Roulette",
+  blackjack: "Blackjack",
+  crash: "Crash",
+};
+
+const descriptions: Record<string, string> = {
+  slots: "Five reels, five paylines. Match symbols from the left.",
+  roulette: "European single-zero wheel with inside and outside bets.",
+  blackjack: "Six-deck shoe. Blackjack pays 3:2.",
+  crash: "A rising multiplier. Cash out before it crashes.",
+};
+
+const basePath = location.pathname.includes("/play/")
+  ? location.pathname.slice(0, location.pathname.indexOf("/play/"))
+  : "";
+const wsUrl = `${location.protocol === "https:" ? "wss" : "ws"}://${location.host}${basePath}/ws`;
+
+const gateway = new Gateway(wsUrl, {
+  onHello(hello) {
+    serverOffset = hello.time - Date.now();
+    currentUser = hello.user ?? null;
+    gameBadge.textContent = `v${hello.version}`;
+  },
+  onView(next) {
+    view = next;
+    // Game and history views carry no account field; the lobby is the source
+    // of truth for who is signed in. A null lobby user is a logout or an
+    // expired session.
+    if (typeof next.balance === "number") lastBalance = next.balance;
+    if (next.screen === "lobby" && "user" in next) {
+      currentUser = (next.user as string | null) ?? null;
+      if (currentUser) authPass.value = "";
+      else lastBalance = null;
+    }
+    reconnectAttempts = 0;
+    reconnectOverlay.hidden = true;
+    render();
+    if (currentUser && view.balance === null && infoFor !== currentUser) {
+      infoFor = currentUser;
+      gateway.send("Info");
+    }
+    if (!currentUser) infoFor = null;
+  },
+  onNotice(text) {
+    if (
+      text.startsWith("Connected to:") ||
+      text.startsWith("Fingerprint:") ||
+      text.startsWith("User:") ||
+      text.startsWith("Account:") ||
+      text.startsWith("Balance:")
+    ) {
+      return;
+    }
+    toast(text, toneFor(text));
+    if (text.startsWith("Account created")) {
+      setAuthMode("login");
+      authPass.value = "";
+      authUser.focus();
+    }
+    authSubmit.disabled = false;
+    authSubmit.textContent = authMode === "login" ? "Log in" : "Create account";
+  },
+  onError(text) {
+    toast(text, "bad");
+    authSubmit.disabled = false;
+    authSubmit.textContent = authMode === "login" ? "Log in" : "Create account";
+  },
+  onReplaced() {
+    replacedOverlay.hidden = false;
+  },
+  onPong() {
+    /* The gateway answered; the socket is alive. */
+  },
+  onOpen() {
+    reconnectOverlay.hidden = true;
+  },
+  onClosed(willRetry) {
+    if (replacedOverlay.hidden === false) return;
+    if (!willRetry) {
+      reconnectMessage.textContent = "The connection could not be restored. Reload the page to try again.";
+      reconnectOverlay.hidden = false;
+      return;
+    }
+    reconnectAttempts += 1;
+    reconnectMessage.textContent =
+      reconnectAttempts > 1
+        ? "Still trying to reach the game server…"
+        : "Trying to reach the game server…";
+    reconnectOverlay.hidden = false;
+  },
+});
+
+function send(command: unknown): void {
+  gateway.send(command);
+}
+
+function serverNow(): number {
+  return Date.now() + serverOffset;
+}
+
+function setAuthMode(mode: "login" | "register"): void {
+  authMode = mode;
+  tabLogin.classList.toggle("active", mode === "login");
+  tabRegister.classList.toggle("active", mode === "register");
+  authSubmit.textContent = mode === "login" ? "Log in" : "Create account";
+  authPass.autocomplete = mode === "login" ? "current-password" : "new-password";
+  authError.textContent = "";
+}
+
+function show(screen: "auth" | "lobby" | "game" | "history"): void {
+  authScreen.hidden = screen !== "auth";
+  lobbyScreen.hidden = screen !== "lobby";
+  gameScreen.hidden = screen !== "game";
+  historyScreen.hidden = screen !== "history";
+}
+
+function setBalance(balance: number | null | undefined): void {
+  accountBalance.textContent = money(balance ?? null);
+}
+
+function render(): void {
+  if (!view) return;
+  const user = currentUser;
+  if (user) {
+    sessionBar.hidden = false;
+    accountName.textContent = String(user);
+  } else {
+    sessionBar.hidden = true;
+  }
+
+  setBalance(lastBalance);
+
+  if (!user) {
+    show("auth");
+    authError.textContent = view.login_error ? String(view.login_error) : "";
+    if (view.screen === "lobby" && view.connected === false) {
+      authError.textContent = "The game server is not reachable yet. Retrying…";
+    }
+    return;
+  }
+
+  switch (view.screen) {
+    case "lobby":
+      show("lobby");
+      renderLobby(view);
+      break;
+    case "history":
+      show("history");
+      renderHistory(historyBody, view);
+      break;
+    case "slots":
+    case "roulette":
+    case "blackjack":
+    case "crash":
+      show("game");
+      gameTitle.textContent = titles[view.screen] ?? view.screen;
+      gameBadge.textContent = badge(view);
+      if (view.screen === "slots") renderSlots(gameBoard, gameSide, view, send);
+      else if (view.screen === "roulette") renderRoulette(gameBoard, gameSide, view, send);
+      else if (view.screen === "blackjack") renderBlackjack(gameBoard, gameSide, view, send);
+      else renderCrash(gameBoard, gameSide, view, send, { now: serverNow });
+      break;
+    default:
+      show("auth");
+  }
+}
+
+function badge(view: View): string {
+  if (view.screen === "crash") return String(view.status ?? "");
+  if (view.screen === "blackjack") return String(view.status ?? "");
+  if (view.screen === "slots") return String(view.phase ?? "");
+  if (view.screen === "roulette") return String(view.phase ?? "");
+  return "";
+}
+
+function renderLobby(lobby: View): void {
+  gameGrid.replaceChildren();
+  const list: [string, string][] = lobby.games ?? [];
+  for (const [id, name] of list) {
+    const card = node("article", `game-card ${id}`);
+    card.append(node("h3", undefined, name || titles[id] || id));
+    card.append(node("p", undefined, descriptions[id] ?? "Play a round."));
+
+    const row = node("div", "row wrap");
+    const label = node("label", "field");
+    label.style.flex = "1";
+    label.append(node("span", "label", "Bet"));
+    const input = node("input", "input bet-input") as HTMLInputElement;
+    input.type = "number";
+    input.min = "1";
+    input.step = "10";
+    input.value = String(bets.get(id) ?? 10);
+    input.addEventListener("change", () => {
+      const value = Math.max(1, Math.floor(Number(input.value) || 1));
+      input.value = String(value);
+      bets.set(id, value);
+    });
+    label.append(input);
+
+    const play = node("button", "btn primary", id === "roulette" ? "Open table" : "Play");
+    play.addEventListener("click", () => {
+      const bet = Math.max(1, Math.floor(Number(input.value) || 1));
+      bets.set(id, bet);
+      send({ Play: { game: id, bet } });
+    });
+    row.append(label, play);
+    card.append(row);
+    gameGrid.append(card);
+  }
+
+  if (list.length === 0) {
+    gameGrid.append(node("p", "muted", "The server did not advertise any games."));
+  }
+}
+
+// Auth tabs and form -------------------------------------------------------
+tabLogin.addEventListener("click", () => setAuthMode("login"));
+tabRegister.addEventListener("click", () => setAuthMode("register"));
+
+authForm.addEventListener("submit", async (event) => {
+  event.preventDefault();
+  const user = authUser.value.trim();
+  const password = authPass.value;
+  if (!user || !password) {
+    authError.textContent = "Enter a username and a password.";
+    return;
+  }
+  authSubmit.disabled = true;
+  authSubmit.textContent = "Working…";
+  authError.textContent = "";
+  try {
+    const credential = await sha256Hex(password);
+    if (authMode === "login") {
+      send({ Login: { user, credential } });
+    } else {
+      send({ Register: { user, credential } });
+    }
+  } catch {
+    authError.textContent = "This browser cannot hash the password (needs a secure context).";
+    authSubmit.disabled = false;
+    authSubmit.textContent = authMode === "login" ? "Log in" : "Create account";
+  }
+});
+
+// Chrome and navigation ----------------------------------------------------
+byId("logout").addEventListener("click", () => send("Logout"));
+byId("show-history").addEventListener("click", () => send({ History: { limit: 50 } }));
+byId("refresh-lobby").addEventListener("click", () => send("Info"));
+byId("history-back").addEventListener("click", () => send("ShowLobby"));
+byId("leave-game").addEventListener("click", () => {
+  if (!view) return;
+  const live =
+    (view.screen === "blackjack" && view.status === "player") ||
+    (view.screen === "crash" && view.status === "running");
+  if (live && !window.confirm("Leaving now forfeits the active bet. Continue?")) return;
+  send("Leave");
+});
+byId("reload-replaced").addEventListener("click", () => location.reload());
+byId("reload-reconnect").addEventListener("click", () => location.reload());
+
+window.addEventListener("resize", () => {
+  window.clearTimeout((window as any).__resizeTimer);
+  (window as any).__resizeTimer = window.setTimeout(() => {
+    if (view) render();
+  }, 140);
+});
+
+// A periodic ping keeps the gateway session visibly alive and refreshes the
+// server clock estimate without changing game state.
+window.setInterval(() => {
+  if (currentUser) gateway.ping();
+}, 25_000);
+
+gateway.connect();
diff --git a/web/play/src/net.ts b/web/play/src/net.ts
new file mode 100644
index 0000000..0a963ba
--- /dev/null
+++ b/web/play/src/net.ts
@@ -0,0 +1,120 @@
+import type { Handlers } from "./types";
+
+const MAX_ATTEMPTS = 6;
+
+/**
+ * Browser side of the gateway socket.
+ *
+ * The cookie is HttpOnly and handled by the browser; this class never reads or
+ * stores a credential. A transient close reconnects inside the gateway's grace
+ * window; a deliberate takeover stops for good.
+ */
+export class Gateway {
+  private socket: WebSocket | null = null;
+  private stopped = false;
+  private replaced = false;
+  private attempts = 0;
+  private timer: number | undefined;
+
+  constructor(
+    private readonly url: string,
+    private readonly handlers: Handlers,
+  ) {}
+
+  connect(): void {
+    if (this.stopped) return;
+    this.clearTimer();
+
+    let socket: WebSocket;
+    try {
+      socket = new WebSocket(this.url);
+    } catch {
+      const retrying = this.scheduleReconnect();
+      if (!retrying) this.handlers.onClosed(false);
+      return;
+    }
+    this.socket = socket;
+
+    socket.addEventListener("open", () => {
+      this.attempts = 0;
+      this.handlers.onOpen();
+    });
+
+    socket.addEventListener("message", (event) => {
+      let message: any;
+      try {
+        message = JSON.parse(String(event.data));
+      } catch {
+        return;
+      }
+      switch (message.type) {
+        case "hello":
+          this.handlers.onHello(message);
+          break;
+        case "view":
+          this.handlers.onView(message.view);
+          break;
+        case "notice":
+          this.handlers.onNotice(String(message.text ?? ""));
+          break;
+        case "error":
+          this.handlers.onError(String(message.text ?? ""));
+          break;
+        case "replaced":
+          this.replaced = true;
+          this.handlers.onReplaced();
+          break;
+        case "pong":
+          this.handlers.onPong();
+          break;
+      }
+    });
+
+    socket.addEventListener("close", () => {
+      const wasThisSocket = this.socket === socket;
+      if (wasThisSocket) this.socket = null;
+      if (this.replaced || this.stopped) {
+        this.handlers.onClosed(false);
+        return;
+      }
+      const retrying = this.scheduleReconnect();
+      this.handlers.onClosed(retrying);
+    });
+
+    socket.addEventListener("error", () => {
+      // The close event follows; reconnect is scheduled there.
+    });
+  }
+
+  send(command: unknown): void {
+    if (this.socket?.readyState !== WebSocket.OPEN) return;
+    this.socket.send(JSON.stringify({ type: "command", command }));
+  }
+
+  ping(): void {
+    if (this.socket?.readyState === WebSocket.OPEN) {
+      this.socket.send(JSON.stringify({ type: "ping" }));
+    }
+  }
+
+  close(): void {
+    this.stopped = true;
+    this.clearTimer();
+    this.socket?.close();
+  }
+
+  private scheduleReconnect(): boolean {
+    if (this.stopped || this.replaced || this.attempts >= MAX_ATTEMPTS) return false;
+    this.attempts += 1;
+    const delay = Math.min(250 * 2 ** (this.attempts - 1), 4000);
+    this.timer = window.setTimeout(() => this.connect(), delay);
+    return true;
+  }
+
+  private clearTimer(): void {
+    if (this.timer !== undefined) {
+      window.clearTimeout(this.timer);
+      this.timer = undefined;
+    }
+  }
+}
diff --git a/web/play/src/roulette.ts b/web/play/src/roulette.ts
new file mode 100644
index 0000000..cbb7c6e
--- /dev/null
+++ b/web/play/src/roulette.ts
@@ -0,0 +1,474 @@
+import type { View } from "./types";
+import { clear, money, node } from "./dom";
+
+type Zone = {
+  x: number;
+  y: number;
+  w: number;
+  h: number;
+  target: any;
+  label: string;
+  kind: "number" | "zero" | "dozen" | "column" | "outside";
+  number?: number;
+};
+
+type Hotspot = {
+  x: number;
+  y: number;
+  radius: number;
+  target: any;
+  rank: number;
+};
+
+type Layout = {
+  width: number;
+  height: number;
+  cellW: number;
+  cellH: number;
+  zeroX: number;
+  zeroW: number;
+  gridX: number;
+  gridY: number;
+  gridW: number;
+  columnX: number;
+  dozensY: number;
+  outsideY: number;
+  outsideH: number;
+  zones: Zone[];
+  hotspots: Hotspot[];
+};
+
+const RED = "#b0313a";
+const BLACK = "#151b21";
+const ZERO = "#106b45";
+const FELT = "#0d5c39";
+const FELT_DARK = "#09472c";
+const FELT_LINE = "#1f7d52";
+const TEXT = "#ecf7f0";
+const GOLD = "#e0b64a";
+
+function colorOf(number: number): string {
+  if (number === 0) return "green";
+  const reds = [1, 3, 5, 7, 9, 12, 14, 16, 18, 19, 21, 23, 25, 27, 30, 32, 34, 36];
+  return reds.includes(number) ? "red" : "black";
+}
+
+function layout(width: number, height: number): Layout {
+  const pad = 14;
+  const zeroW = Math.max(38, width * 0.055);
+  const columnW = Math.max(34, width * 0.05);
+  const outsideH = Math.max(30, height * 0.07);
+  const gap = 6;
+  const gridW = width - pad * 2 - zeroW - columnW;
+  const cellW = gridW / 12;
+  const cellH = (height - pad * 2 - outsideH * 2 - gap * 2) / 3;
+  const gridX = pad + zeroW;
+  const gridY = pad;
+  const dozensY = gridY + cellH * 3 + gap;
+  const outsideY = dozensY + outsideH + gap;
+  const zones: Zone[] = [];
+
+  for (let column = 0; column < 12; column += 1) {
+    for (let row = 0; row < 3; row += 1) {
+      const number = column * 3 + (3 - row);
+      zones.push({
+        x: gridX + column * cellW,
+        y: gridY + row * cellH,
+        w: cellW,
+        h: cellH,
+        target: { bet: "straight", number },
+        label: String(number),
+        kind: "number",
+        number,
+      });
+    }
+  }
+
+  zones.push({
+    x: pad,
+    y: gridY,
+    w: zeroW,
+    h: cellH * 3,
+    target: { bet: "straight", number: 0 },
+    label: "0",
+    kind: "zero",
+    number: 0,
+  });
+
+  for (let top = 0; top < 3; top += 1) {
+    const index = 2 - top;
+    zones.push({
+      x: gridX + gridW,
+      y: gridY + top * cellH,
+      w: columnW,
+      h: cellH,
+      target: { bet: "column", index },
+      label: "2:1",
+      kind: "column",
+    });
+  }
+
+  for (let index = 0; index < 3; index += 1) {
+    zones.push({
+      x: gridX + (gridW / 3) * index,
+      y: dozensY,
+      w: gridW / 3,
+      h: outsideH,
+      target: { bet: "dozen", index },
+      label: ["1st 12", "2nd 12", "3rd 12"][index],
+      kind: "dozen",
+    });
+  }
+
+  const outside = [
+    { kind: "low", label: "1–18" },
+    { kind: "even", label: "EVEN" },
+    { kind: "red", label: "RED" },
+    { kind: "black", label: "BLACK" },
+    { kind: "odd", label: "ODD" },
+    { kind: "high", label: "19–36" },
+  ];
+  outside.forEach((item, index) => {
+    zones.push({
+      x: gridX + (gridW / 6) * index,
+      y: outsideY,
+      w: gridW / 6,
+      h: outsideH,
+      target: { bet: "outside", kind: item.kind },
+      label: item.label,
+      kind: "outside",
+    });
+  });
+
+  // Split and corner hotspots sit on the lines between cells, like the real
+  // felt (and the desktop fine lattice). Corners rank ahead of splits.
+  const hotspots: Hotspot[] = [];
+  const cellCenter = (number: number) => {
+    const cell = zones.find((zone) => zone.kind === "number" && zone.number === number);
+    return cell ? { x: cell.x + cell.w / 2, y: cell.y + cell.h / 2 } : null;
+  };
+
+  for (let column = 0; column < 11; column += 1) {
+    for (let row = 0; row < 2; row += 1) {
+      const top = column * 3 + (3 - row);
+      hotspots.push({
+        x: gridX + (column + 1) * cellW,
+        y: gridY + (row + 1) * cellH,
+        radius: 12,
+        rank: 0,
+        target: { bet: "corner", numbers: [top, top - 1, top + 3, top + 2] },
+      });
+    }
+  }
+
+  for (let column = 0; column < 12; column += 1) {
+    for (let row = 0; row < 2; row += 1) {
+      const top = column * 3 + (3 - row);
+      const center = cellCenter(top);
+      if (!center) continue;
+      hotspots.push({
+        x: center.x,
+        y: gridY + (row + 1) * cellH,
+        radius: 10,
+        rank: 1,
+        target: { bet: "split", a: top, b: top - 1 },
+      });
+    }
+  }
+
+  for (let column = 0; column < 11; column += 1) {
+    for (let row = 0; row < 3; row += 1) {
+      const left = column * 3 + (3 - row);
+      hotspots.push({
+        x: gridX + (column + 1) * cellW,
+        y: gridY + row * cellH + cellH / 2,
+        radius: 10,
+        rank: 1,
+        target: { bet: "split", a: left, b: left + 3 },
+      });
+    }
+  }
+
+  for (let row = 0; row < 3; row += 1) {
+    const number = 3 - row;
+    hotspots.push({
+      x: gridX,
+      y: gridY + row * cellH + cellH / 2,
+      radius: 10,
+      rank: 1,
+      target: { bet: "split", a: 0, b: number },
+    });
+  }
+
+  return {
+    width,
+    height,
+    cellW,
+    cellH,
+    zeroX: pad,
+    zeroW,
+    gridX,
+    gridY,
+    gridW,
+    columnX: gridX + gridW,
+    dozensY,
+    outsideY,
+    outsideH,
+    zones,
+    hotspots,
+  };
+}
+
+function roundRect(
+  ctx: CanvasRenderingContext2D,
+  x: number,
+  y: number,
+  w: number,
+  h: number,
+  radius: number,
+): void {
+  const r = Math.min(radius, w / 2, h / 2);
+  ctx.beginPath();
+  ctx.moveTo(x + r, y);
+  ctx.arcTo(x + w, y, x + w, y + h, r);
+  ctx.arcTo(x + w, y + h, x, y + h, r);
+  ctx.arcTo(x, y + h, x, y, r);
+  ctx.arcTo(x, y, x + w, y, r);
+  ctx.closePath();
+}
+
+function draw(canvas: HTMLCanvasElement, view: View): Layout {
+  const width = canvas.clientWidth || 800;
+  const height = canvas.clientHeight || 540;
+  const dpr = window.devicePixelRatio || 1;
+  if (canvas.width !== Math.round(width * dpr) || canvas.height !== Math.round(height * dpr)) {
+    canvas.width = Math.round(width * dpr);
+    canvas.height = Math.round(height * dpr);
+  }
+  const ctx = canvas.getContext("2d");
+  const map = layout(width, height);
+  if (!ctx) return map;
+  ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
+  ctx.clearRect(0, 0, width, height);
+  ctx.fillStyle = FELT_DARK;
+  roundRect(ctx, 0, 0, width, height, 10);
+  ctx.fill();
+
+  for (const zone of map.zones) {
+    let fill = FELT;
+    if (zone.kind === "number") fill = zone.number === 0 ? ZERO : colorOf(zone.number!) === "red" ? RED : BLACK;
+    else if (zone.kind === "zero") fill = ZERO;
+    ctx.fillStyle = fill;
+    ctx.strokeStyle = FELT_LINE;
+    ctx.lineWidth = 1;
+    roundRect(ctx, zone.x + 1, zone.y + 1, zone.w - 2, zone.h - 2, 3);
+    ctx.fill();
+    ctx.stroke();
+
+    ctx.fillStyle = TEXT;
+    ctx.textAlign = "center";
+    ctx.textBaseline = "middle";
+    if (zone.kind === "number" || zone.kind === "zero") {
+      ctx.font = `700 ${Math.min(24, map.cellH * 0.3)}px ui-monospace, monospace`;
+    } else {
+      ctx.font = `600 ${Math.min(12, map.outsideH * 0.4)}px ui-monospace, monospace`;
+    }
+    ctx.fillText(zone.label, zone.x + zone.w / 2, zone.y + zone.h / 2);
+  }
+
+  drawChips(ctx, map, view);
+  return map;
+}
+
+function targetKey(target: any): string {
+  return JSON.stringify(target);
+}
+
+function centerFor(layout: Layout, target: any): { x: number; y: number } | null {
+  const key = targetKey(target);
+  const exact = layout.zones.find((zone) => targetKey(zone.target) === key);
+  if (exact) return { x: exact.x + exact.w / 2, y: exact.y + exact.h / 2 };
+
+  // Split and corner bets are reachable from the desktop's fine lattice. A
+  // browser session can still show them: average the covered number cells.
+  if (target?.bet === "split" || target?.bet === "corner") {
+    const numbers: number[] = target.bet === "split" ? [target.a, target.b] : target.numbers;
+    const cells = layout.zones.filter(
+      (zone) => (zone.kind === "number" || zone.kind === "zero") && numbers.includes(zone.number!),
+    );
+    if (cells.length > 0) {
+      return {
+        x: cells.reduce((sum, cell) => sum + cell.x + cell.w / 2, 0) / cells.length,
+        y: cells.reduce((sum, cell) => sum + cell.y + cell.h / 2, 0) / cells.length,
+      };
+    }
+  }
+  return null;
+}
+
+function drawChips(ctx: CanvasRenderingContext2D, map: Layout, view: View): void {
+  const chips: any[] = view.bets?.chips ?? [];
+  for (const chip of chips) {
+    const center = centerFor(map, chip.target);
+    if (!center) continue;
+    const radius = Math.max(12, Math.min(18, map.cellW * 0.26));
+    ctx.beginPath();
+    ctx.arc(center.x, center.y, radius, 0, Math.PI * 2);
+    ctx.fillStyle = GOLD;
+    ctx.fill();
+    ctx.strokeStyle = "#7a5a12";
+    ctx.lineWidth = 2;
+    ctx.stroke();
+    ctx.fillStyle = "#221a05";
+    ctx.textAlign = "center";
+    ctx.textBaseline = "middle";
+    ctx.font = `700 ${radius > 15 ? 11 : 10}px ui-monospace, monospace`;
+    ctx.fillText(String(chip.amount), center.x, center.y + 0.5);
+  }
+}
+
+export function renderRoulette(
+  board: HTMLElement,
+  side: HTMLElement,
+  view: View,
+  send: (command: unknown) => void,
+): void {
+  clear(board);
+  clear(side);
+
+  const spinning = view.phase === "spinning";
+  board.append(node("h2", undefined, "Roulette"));
+  board.append(
+    node(
+      "p",
+      "note",
+      "European single-zero wheel. Click a number, line or corner to add a chip; right-click takes one back.",
+    ),
+  );
+
+  const wrap = node("div", "roulette-wrap");
+  const canvas = node("canvas", "roulette-canvas") as HTMLCanvasElement;
+  wrap.append(canvas);
+
+  if (view.phase === "result" && view.number !== null && view.number !== undefined) {
+    const result = node("div", `wheel-result ${view.color ?? ""}`);
+    result.append(node("div", "label", "Result"));
+    result.append(node("div", "num", String(view.number)));
+    const winnings = Number(view.winnings ?? 0);
+    result.append(node("div", "note", winnings > 0 ? `Won ${money(winnings)}` : "No win"));
+    wrap.append(result);
+  }
+  board.append(wrap);
+
+  // The canvas must be in the document before its client size is read.
+  const map = draw(canvas, view);
+  let current = map;
+
+  const hit = (clientX: number, clientY: number): Zone | null => {
+    const rect = canvas.getBoundingClientRect();
+    const x = clientX - rect.left;
+    const y = clientY - rect.top;
+
+    let best: Hotspot | null = null;
+    for (const hotspot of current.hotspots) {
+      const distance = Math.hypot(x - hotspot.x, y - hotspot.y);
+      if (distance > hotspot.radius) continue;
+      if (!best || hotspot.rank < best.rank || (hotspot.rank === best.rank && distance < Math.hypot(x - best.x, y - best.y))) {
+        best = hotspot;
+      }
+    }
+    if (best) {
+      return {
+        x: best.x - best.radius,
+        y: best.y - best.radius,
+        w: best.radius * 2,
+        h: best.radius * 2,
+        target: best.target,
+        label: "",
+        kind: "number",
+      };
+    }
+
+    for (let index = current.zones.length - 1; index >= 0; index -= 1) {
+      const zone = current.zones[index];
+      if (x >= zone.x && x <= zone.x + zone.w && y >= zone.y && y <= zone.y + zone.h) {
+        return zone;
+      }
+    }
+    return null;
+  };
+
+  canvas.addEventListener("click", (event) => {
+    if (spinning) return;
+    const zone = hit(event.clientX, event.clientY);
+    if (zone) send({ PlaceBetAt: zone.target });
+  });
+  canvas.addEventListener("contextmenu", (event) => {
+    event.preventDefault();
+    if (spinning) return;
+    const zone = hit(event.clientX, event.clientY);
+    if (zone) send({ RemoveBetAt: zone.target });
+  });
+  canvas.addEventListener("mousemove", (event) => {
+    const zone = hit(event.clientX, event.clientY);
+    canvas.style.cursor = zone && !spinning ? "pointer" : "default";
+  });
+  new ResizeObserver(() => {
+    current = draw(canvas, view);
+  }).observe(canvas);
+
+  // Sidebar
+  side.append(node("div", "label", "Roulette"));
+  side.append(node("p", "note", "Chips sit on the felt. The total is reserved when you spin."));
+
+  side.append(node("div", "label", "Chip"));
+  const chipRow = node("div", "chip-row");
+  for (const value of [10, 25, 50, 100, 500]) {
+    const button = node("button", `chip-btn ${Number(view.chip) === value ? "active" : ""}`, String(value));
+    button.disabled = spinning;
+    button.addEventListener("click", () => send({ SetChip: value }));
+    chipRow.append(button);
+  }
+  side.append(chipRow);
+
+  const total = (view.bets?.chips ?? []).reduce(
+    (sum: number, chip: any) => sum + Number(chip.amount ?? 0),
+    0,
+  );
+  const totalRow = node("div", "stat");
+  totalRow.append(node("span", "muted", "On the felt"), node("strong", "mono", money(total)));
+  side.append(totalRow);
+
+  if (view.balance !== null && view.balance !== undefined) {
+    const balanceRow = node("div", "stat");
+    balanceRow.append(node("span", "muted", "Balance"), node("strong", "mono", money(Number(view.balance))));
+    side.append(balanceRow);
+  }
+
+  if (view.error) side.append(node("p", "error-text", String(view.error)));
+
+  const status = node("p", "note");
+  if (spinning) status.textContent = "Spinning…";
+  else if (view.phase === "result") {
+    const winnings = Number(view.winnings ?? 0);
+    status.textContent = `${view.number} ${view.color} · ${winnings > 0 ? `won ${money(winnings)}` : "no win"}`;
+    status.className = winnings > 0 ? "note win-text" : "note";
+  } else status.textContent = total > 0 ? "Ready to spin." : "Place at least one chip.";
+  side.append(status);
+
+  const actions = node("div", "actions");
+  const spin = node("button", "btn primary wide big", spinning ? "SPINNING…" : "SPIN WHEEL");
+  spin.disabled = spinning || total === 0;
+  spin.addEventListener("click", () => send("Spin"));
+  const clearBets = node("button", "btn wide", "Clear bets");
+  clearBets.disabled = spinning || total === 0;
+  clearBets.addEventListener("click", () => send("ClearBets"));
+  const leave = node("button", "btn ghost wide", "Leave table");
+  leave.disabled = spinning;
+  leave.addEventListener("click", () => {
+    if (spinning) return;
+    send("Leave");
+  });
+  actions.append(spin, clearBets, leave);
+  side.append(actions);
+}
diff --git a/web/play/src/slots.ts b/web/play/src/slots.ts
new file mode 100644
index 0000000..dba1e25
--- /dev/null
+++ b/web/play/src/slots.ts
@@ -0,0 +1,144 @@
+import type { View } from "./types";
+import { clear, money, node } from "./dom";
+
+const REELS = 5;
+const ROWS = 3;
+const SYMBOLS = "CLOGDS";
+const LINE_NAMES = ["top", "middle", "bottom", "V", "inverted V"];
+
+let spinUntil = 0;
+let animation: number | undefined;
+let latest: View | null = null;
+let latestBoard: HTMLElement | null = null;
+
+export function requestSlotsSpin(): void {
+  spinUntil = Date.now() + 900;
+}
+
+function spinning(view: View): boolean {
+  return view.phase === "spinning" || Date.now() < spinUntil;
+}
+
+export function renderSlots(
+  board: HTMLElement,
+  side: HTMLElement,
+  view: View,
+  send: (command: unknown) => void,
+): void {
+  latest = view;
+  latestBoard = board;
+  if (animation !== undefined) {
+    window.clearInterval(animation);
+    animation = undefined;
+  }
+
+  const active = spinning(view);
+  clear(board);
+  clear(side);
+
+  const title = node("h2", undefined, "Slots");
+  const note = node("p", "note", "Match three or more symbols from the left. Five paylines.");
+  board.append(title, note);
+
+  const reels = node("div", "reels");
+  const tiles: HTMLElement[] = [];
+  const flat = String(view.reels ?? "");
+  for (let column = 0; column < REELS; column += 1) {
+    const reel = node("div", "reel");
+    for (let row = 0; row < ROWS; row += 1) {
+      const index = column * ROWS + row;
+      const symbol = active
+        ? SYMBOLS[(index * 3 + Math.floor(Date.now() / 70)) % SYMBOLS.length]
+        : flat.length === REELS * ROWS
+          ? flat[index]
+          : flat.length === REELS
+            ? flat[column]
+            : SYMBOLS[(index * 5 + column) % SYMBOLS.length];
+      const tile = node("div", "tile", symbol);
+      tile.classList.add(`sym-${symbol}`);
+      if (active) tile.classList.add("spinning");
+      if (!active && (view.win_cells ?? []).includes(index)) tile.classList.add("win");
+      tiles.push(tile);
+      reel.append(tile);
+    }
+    reels.append(reel);
+  }
+  board.append(reels);
+
+  const lines = node("div", "win-lines");
+  if (!active && view.phase === "result") {
+    const winnings = Number(view.winnings ?? 0);
+    if (winnings > 0) {
+      const names = (view.win_lines ?? [])
+        .map((line: number) => `${line} (${LINE_NAMES[line - 1] ?? "line"})`)
+        .join("  ·  ");
+      lines.textContent = `${view.win_type === "mega" ? "MEGA WIN" : view.win_type === "big" ? "BIG WIN" : "WIN"} ${money(winnings)}${names ? `  ·  ${names}` : ""}`;
+      lines.classList.add("win-text");
+    } else {
+      lines.textContent = "No win — spin again.";
+    }
+  } else if (active) {
+    lines.textContent = "Spinning…";
+  } else {
+    lines.textContent = "Pick a bet and spin.";
+  }
+  board.append(lines);
+
+  if (active) {
+    let tick = 0;
+    animation = window.setInterval(() => {
+      tick += 1;
+      for (let index = 0; index < tiles.length; index += 1) {
+        const symbol = SYMBOLS[(index * 3 + tick) % SYMBOLS.length];
+        tiles[index].textContent = symbol;
+        tiles[index].className = `tile spinning sym-${symbol}`;
+      }
+      if (Date.now() >= spinUntil && latest && latestBoard) {
+        window.clearInterval(animation);
+        animation = undefined;
+        renderSlots(latestBoard, side, latest, send);
+      }
+    }, 70);
+  }
+
+  // Sidebar
+  side.append(node("div", "label", "Slots"));
+  side.append(node("p", "note", "5 reels × 3 rows, 5 paylines."));
+
+  const betRow = node("div", "row");
+  const minus = node("button", "btn small", "−10");
+  const bet = node("strong", "mono", money(Number(view.bet ?? 0)));
+  const plus = node("button", "btn small", "+10");
+  minus.disabled = active;
+  plus.disabled = active;
+  minus.addEventListener("click", () => send({ AdjustBet: -10 }));
+  plus.addEventListener("click", () => send({ AdjustBet: 10 }));
+  betRow.append(minus, bet, plus);
+  side.append(node("div", "label", "Bet"), betRow);
+
+  if (view.error) {
+    side.append(node("p", "error-text", String(view.error)));
+  }
+
+  const status = node("p", "note");
+  if (active) status.textContent = "Spinning…";
+  else if (view.phase === "result") {
+    const winnings = Number(view.winnings ?? 0);
+    status.textContent = winnings > 0 ? `Won ${money(winnings)}` : "No win this spin.";
+    if (winnings > 0) status.classList.add("win-text");
+  } else status.textContent = "Ready when you are.";
+  side.append(status);
+
+  const actions = node("div", "actions");
+  const spin = node("button", "btn primary wide big", active ? "SPINNING…" : "SPIN");
+  spin.disabled = active;
+  spin.addEventListener("click", () => {
+    requestSlotsSpin();
+    send("Spin");
+  });
+  const leave = node("button", "btn ghost wide", "Leave machine");
+  leave.disabled = active;
+  leave.addEventListener("click", () => send("Leave"));
+  actions.append(spin, leave);
+  side.append(actions);
+}
diff --git a/web/play/src/types.ts b/web/play/src/types.ts
new file mode 100644
index 0000000..e594a0b
--- /dev/null
+++ b/web/play/src/types.ts
@@ -0,0 +1,27 @@
+export type View = {
+  screen: "lobby" | "history" | "slots" | "roulette" | "blackjack" | "crash";
+  [key: string]: any;
+};
+
+export type Hello = {
+  type: "hello";
+  version: string;
+  grace_seconds: number;
+  /** Signed-in user restored after a refresh, if any. */
+  user?: string | null;
+  /** Estimated game-server Unix time in milliseconds. */
+  time: number;
+};
+
+export type Send = (command: unknown) => void;
+
+export type Handlers = {
+  onHello: (hello: Hello) => void;
+  onView: (view: View) => void;
+  onNotice: (text: string) => void;
+  onError: (text: string) => void;
+  onReplaced: () => void;
+  onPong: () => void;
+  onOpen: () => void;
+  onClosed: (willRetry: boolean) => void;
+};
diff --git a/web/play/style.css b/web/play/style.css
new file mode 100644
index 0000000..20842d2
--- /dev/null
+++ b/web/play/style.css
@@ -0,0 +1,407 @@
+:root {
+  --bg: #0a0e12;
+  --surface: #11171d;
+  --raised: #171f27;
+  --hover: #1d2731;
+  --line: #242e38;
+  --text: #d9e2ea;
+  --dim: #8a98a6;
+  --faint: #5b6773;
+  --accent: #4fb8c9;
+  --win: #4ec27b;
+  --loss: #e05a5a;
+  --gold: #e0b64a;
+  --felt: #0d5c39;
+  --felt-dark: #09472c;
+  --felt-line: #1f7d52;
+  --felt-text: #ecf7f0;
+  --red: #b0313a;
+  --black: #151b21;
+  --zero: #106b45;
+  --radius-sm: 4px;
+  --radius-md: 8px;
+  --radius-lg: 12px;
+  --sans: "Open Sans", ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
+  --mono: "Hack", ui-monospace, "SFMono-Regular", "Cascadia Code", monospace;
+}
+
+* { box-sizing: border-box; }
+html, body { height: 100%; }
+body {
+  margin: 0;
+  background:
+    radial-gradient(1100px 600px at 80% -10%, rgba(79, 184, 201, 0.06), transparent 60%),
+    var(--bg);
+  color: var(--text);
+  font-family: var(--sans);
+  font-size: 14px;
+  line-height: 1.5;
+  -webkit-font-smoothing: antialiased;
+}
+[hidden] { display: none !important; }
+
+a { color: var(--accent); text-decoration: none; }
+a:hover { text-decoration: underline; }
+button, input { font: inherit; color: inherit; }
+button { cursor: pointer; }
+button:disabled { cursor: not-allowed; opacity: 0.45; }
+
+.shell { min-height: 100%; display: flex; flex-direction: column; }
+
+.topbar {
+  display: flex;
+  align-items: center;
+  gap: 16px;
+  min-height: 64px;
+  padding: 0 24px;
+  border-bottom: 1px solid var(--line);
+  background: rgba(10, 14, 18, 0.86);
+  backdrop-filter: blur(10px);
+  position: sticky;
+  top: 0;
+  z-index: 20;
+}
+.brand {
+  color: var(--text);
+  font-family: var(--mono);
+  font-size: 19px;
+  letter-spacing: 0.04em;
+  white-space: nowrap;
+}
+.brand span { color: var(--win); }
+.brand:hover { text-decoration: none; }
+.tagline {
+  color: var(--faint);
+  font-family: var(--mono);
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.12em;
+}
+.spacer { flex: 1; }
+.session { display: flex; align-items: center; gap: 12px; }
+.session .who { color: var(--dim); font-family: var(--mono); font-size: 12px; }
+.session .who strong { color: var(--text); font-weight: 600; }
+.balance {
+  color: var(--win);
+  font-family: var(--mono);
+  font-size: 16px;
+  padding: 4px 10px;
+  border: 1px solid var(--line);
+  border-radius: var(--radius-sm);
+  background: var(--surface);
+  white-space: nowrap;
+}
+
+main { width: min(1240px, 100%); margin: 0 auto; padding: 28px 24px 64px; flex: 1; }
+
+h1, h2, h3 { margin: 0; font-weight: 600; }
+h1 { font-size: 26px; letter-spacing: -0.01em; }
+h2 { font-size: 18px; }
+.muted { color: var(--dim); }
+.faint { color: var(--faint); }
+.mono { font-family: var(--mono); }
+.label {
+  font-family: var(--mono);
+  font-size: 10px;
+  text-transform: uppercase;
+  letter-spacing: 0.16em;
+  color: var(--dim);
+}
+.error-text { color: var(--loss); }
+.win-text { color: var(--win); }
+
+.btn {
+  border: 1px solid var(--line);
+  background: var(--raised);
+  color: var(--text);
+  padding: 9px 14px;
+  border-radius: var(--radius-md);
+  line-height: 1.2;
+  transition: background 120ms ease, border-color 120ms ease, transform 80ms ease;
+}
+.btn:hover:not(:disabled) { background: var(--hover); border-color: #33404d; }
+.btn:active:not(:disabled) { transform: translateY(1px); }
+.btn.primary {
+  background: var(--win);
+  border-color: var(--win);
+  color: #06120b;
+  font-weight: 700;
+}
+.btn.primary:hover:not(:disabled) { filter: brightness(1.08); }
+.btn.accent {
+  background: rgba(79, 184, 201, 0.14);
+  border-color: var(--accent);
+  color: var(--accent);
+  font-weight: 600;
+}
+.btn.danger {
+  background: rgba(224, 90, 90, 0.12);
+  border-color: rgba(224, 90, 90, 0.55);
+  color: var(--loss);
+}
+.btn.ghost { background: transparent; }
+.btn.small { padding: 5px 9px; font-size: 12px; }
+.btn.wide { width: 100%; }
+.btn.big { padding: 13px 18px; font-size: 15px; }
+
+.input {
+  width: 100%;
+  background: var(--bg);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-md);
+  padding: 10px 12px;
+  outline: none;
+}
+.input:focus { border-color: var(--accent); box-shadow: 0 0 0 2px rgba(79, 184, 201, 0.18); }
+.field { display: grid; gap: 6px; }
+.row { display: flex; align-items: center; gap: 10px; }
+.row.wrap { flex-wrap: wrap; }
+.hr { height: 1px; background: var(--line); border: 0; margin: 18px 0; }
+
+/* Auth */
+.auth-wrap { display: grid; place-items: center; min-height: 52vh; }
+.auth-card {
+  width: min(430px, 100%);
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-lg);
+  padding: 26px;
+  box-shadow: 0 24px 70px rgba(0, 0, 0, 0.35);
+}
+.auth-tabs { display: flex; gap: 4px; margin-bottom: 20px; background: var(--bg); padding: 4px; border-radius: var(--radius-md); }
+.auth-tab { flex: 1; border: 0; background: transparent; color: var(--dim); padding: 8px; border-radius: var(--radius-sm); }
+.auth-tab.active { background: var(--raised); color: var(--text); }
+.auth-card form { display: grid; gap: 14px; }
+.auth-foot { margin-top: 16px; font-size: 12px; color: var(--faint); }
+
+/* Lobby */
+.lobby-head { display: flex; align-items: end; gap: 18px; margin-bottom: 22px; flex-wrap: wrap; }
+.lobby-head .spacer { flex: 1; }
+.game-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; }
+.game-card {
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-lg);
+  padding: 18px;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+  min-height: 178px;
+  position: relative;
+  overflow: hidden;
+}
+.game-card::before {
+  content: "";
+  position: absolute;
+  inset: 0 auto 0 0;
+  width: 3px;
+  background: var(--accent);
+  opacity: 0.7;
+}
+.game-card.crash::before { background: var(--gold); }
+.game-card.roulette::before { background: var(--felt-line); }
+.game-card.blackjack::before { background: var(--loss); }
+.game-card h3 { font-size: 17px; }
+.game-card p { margin: 0; color: var(--dim); font-size: 13px; flex: 1; }
+.game-card .row { justify-content: space-between; }
+.bet-input { width: 92px; }
+
+/* Game shell */
+.game-head { display: flex; align-items: center; gap: 14px; margin-bottom: 18px; }
+.game-head .spacer { flex: 1; }
+.game-body {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) 320px;
+  gap: 16px;
+  align-items: start;
+}
+.board {
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-lg);
+  padding: 18px;
+  min-height: 560px;
+  overflow: hidden;
+}
+.sidebar {
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-lg);
+  padding: 18px;
+  display: flex;
+  flex-direction: column;
+  gap: 14px;
+  position: sticky;
+  top: 84px;
+}
+.sidebar .actions { margin-top: auto; display: grid; gap: 8px; }
+.sidebar .stat { display: flex; justify-content: space-between; gap: 12px; font-size: 13px; }
+.sidebar .stat strong { font-family: var(--mono); font-weight: 600; }
+.note { color: var(--dim); font-size: 12px; }
+.chip-row { display: flex; flex-wrap: wrap; gap: 6px; }
+.chip-btn {
+  font-family: var(--mono);
+  font-size: 12px;
+  border-radius: 999px;
+  border: 1px solid var(--line);
+  background: var(--raised);
+  padding: 5px 10px;
+}
+.chip-btn.active { border-color: var(--gold); color: var(--gold); background: rgba(224, 182, 74, 0.1); }
+
+/* Slots */
+.reels {
+  display: grid;
+  grid-template-columns: repeat(5, minmax(60px, 1fr));
+  gap: 10px;
+  max-width: 760px;
+  margin: 24px auto 0;
+}
+.reel { display: grid; gap: 8px; }
+.tile {
+  aspect-ratio: 1 / 0.92;
+  display: grid;
+  place-items: center;
+  border-radius: var(--radius-md);
+  border: 1px solid var(--line);
+  background: var(--bg);
+  font-family: var(--mono);
+  font-size: clamp(26px, 5vw, 54px);
+  font-weight: 700;
+  color: var(--dim);
+  transition: color 90ms ease, border-color 90ms ease, background 90ms ease;
+}
+.tile.sym-C { color: #c8d1da; }
+.tile.sym-L { color: #7cc4d4; }
+.tile.sym-O { color: #d8c27a; }
+.tile.sym-G { color: #83d09a; }
+.tile.sym-D { color: #d48d8d; }
+.tile.sym-S { color: #e0b64a; }
+.tile.win { border-color: var(--win); background: rgba(78, 194, 123, 0.12); color: var(--win); }
+.tile.spinning { color: var(--faint); }
+.win-lines { text-align: center; margin-top: 18px; color: var(--dim); font-size: 12px; min-height: 18px; }
+
+/* Cards */
+.hand { margin: 16px 0; }
+.hand .label { margin-bottom: 8px; }
+.cards { display: flex; gap: 8px; flex-wrap: wrap; min-height: 116px; }
+.card {
+  width: 76px;
+  height: 108px;
+  border-radius: 9px;
+  background: #f2f5f7;
+  color: #121820;
+  border: 1px solid #cfd8df;
+  padding: 8px;
+  display: flex;
+  flex-direction: column;
+  justify-content: space-between;
+  font-family: var(--mono);
+  font-weight: 700;
+  box-shadow: 0 8px 18px rgba(0, 0, 0, 0.22);
+}
+.card.red { color: #a51f2d; }
+.card.back { background: repeating-linear-gradient(135deg, #1d2731, #1d2731 6px, #26333f 6px, #26333f 12px); border-color: #33404d; }
+.card .rank { font-size: 22px; line-height: 1; }
+.card .suit { font-size: 22px; align-self: flex-end; }
+.card.back .rank, .card.back .suit { color: var(--faint); }
+.total { color: var(--dim); font-family: var(--mono); font-size: 12px; }
+.total strong { color: var(--text); font-size: 15px; }
+.outcome { margin-top: 20px; padding: 14px 16px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--bg); }
+
+/* Crash */
+.crash-wrap { position: relative; }
+.crash-number {
+  font-family: var(--mono);
+  font-size: clamp(44px, 9vw, 86px);
+  line-height: 1;
+  letter-spacing: -0.04em;
+}
+.crash-number.running { color: var(--gold); }
+.crash-number.crashed { color: var(--loss); }
+.crash-number.cashed { color: var(--win); }
+.crash-meta { display: flex; gap: 16px; flex-wrap: wrap; margin-top: 10px; color: var(--faint); font-size: 11px; font-family: var(--mono); }
+.verify { margin-top: 12px; padding: 10px; border: 1px solid var(--line); border-radius: var(--radius-sm); background: var(--bg); font-size: 11px; color: var(--dim); word-break: break-all; }
+.verify.ok { border-color: rgba(78, 194, 123, 0.4); color: var(--win); }
+.verify.bad { border-color: rgba(224, 90, 90, 0.5); color: var(--loss); }
+
+/* Roulette */
+.roulette-wrap { position: relative; }
+canvas { display: block; width: 100%; }
+.roulette-canvas { height: 540px; }
+.crash-canvas { height: 360px; }
+.wheel-result {
+  position: absolute;
+  top: 16px;
+  right: 16px;
+  padding: 8px 12px;
+  border-radius: var(--radius-md);
+  border: 1px solid var(--line);
+  background: rgba(10, 14, 18, 0.86);
+  font-family: var(--mono);
+}
+.wheel-result .num { font-size: 26px; font-weight: 700; }
+.wheel-result.red .num { color: #f06a74; }
+.wheel-result.black .num { color: #dfe8ef; }
+.wheel-result.green .num { color: #66d49a; }
+
+/* History */
+.table-wrap { overflow-x: auto; border: 1px solid var(--line); border-radius: var(--radius-lg); }
+table { width: 100%; border-collapse: collapse; background: var(--surface); }
+th, td { text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--line); font-size: 13px; white-space: nowrap; }
+th { color: var(--dim); font-family: var(--mono); font-size: 10px; text-transform: uppercase; letter-spacing: 0.12em; }
+tr:last-child td { border-bottom: 0; }
+td.num { font-family: var(--mono); }
+td.pos { color: var(--win); }
+td.neg { color: var(--loss); }
+
+/* Toasts and overlays */
+#toasts { position: fixed; right: 18px; bottom: 18px; display: grid; gap: 8px; z-index: 50; width: min(380px, calc(100vw - 36px)); }
+.toast {
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-left: 3px solid var(--accent);
+  border-radius: var(--radius-md);
+  padding: 10px 12px;
+  font-size: 13px;
+  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.35);
+  animation: toast-in 160ms ease-out;
+}
+.toast.good { border-left-color: var(--win); }
+.toast.bad { border-left-color: var(--loss); }
+@keyframes toast-in { from { opacity: 0; transform: translateY(6px); } }
+.overlay {
+  position: fixed;
+  inset: 0;
+  background: rgba(5, 8, 11, 0.78);
+  display: grid;
+  place-items: center;
+  z-index: 60;
+  padding: 24px;
+}
+.modal {
+  width: min(440px, 100%);
+  background: var(--surface);
+  border: 1px solid var(--line);
+  border-radius: var(--radius-lg);
+  padding: 24px;
+  text-align: center;
+}
+.modal p { color: var(--dim); }
+
+@media (max-width: 900px) {
+  .game-body { grid-template-columns: 1fr; }
+  .sidebar { position: static; }
+  .tagline { display: none; }
+}
+@media (max-width: 620px) {
+  main { padding: 18px 14px 54px; }
+  .topbar { padding: 0 14px; gap: 10px; }
+  .session .who { display: none; }
+  .balance { font-size: 14px; }
+  .reels { gap: 6px; }
+  .tile { font-size: clamp(18px, 7vw, 34px); }
+  .card { width: 58px; height: 84px; }
+  .crash-canvas { height: 260px; }
+  .roulette-canvas { height: 400px; }
+}
diff --git a/web/play/test/smoke.mjs b/web/play/test/smoke.mjs
new file mode 100644
index 0000000..c1274bc
--- /dev/null
+++ b/web/play/test/smoke.mjs
@@ -0,0 +1,294 @@
+import fs from "node:fs";
+import { webcrypto } from "node:crypto";
+import { JSDOM, VirtualConsole } from "jsdom";
+
+const html = fs.readFileSync(new URL("../index.html", import.meta.url), "utf8")
+  .replace('<script src="app.js" defer></script>', "");
+const bundle = fs.readFileSync(new URL("../app.js", import.meta.url), "utf8");
+
+const failures = [];
+const virtualConsole = new VirtualConsole();
+virtualConsole.on("jsdomError", (error) => failures.push(String(error)));
+
+const dom = new JSDOM(html, {
+  url: "http://127.0.0.1:8899/play/",
+  runScripts: "outside-only",
+  pretendToBeVisual: true,
+  virtualConsole,
+});
+const { window } = dom;
+
+Object.defineProperty(window, "crypto", { value: webcrypto });
+window.devicePixelRatio = 1;
+window.confirm = () => true;
+
+class MockWebSocket {
+  static OPEN = 1;
+  static instances = [];
+  readyState = MockWebSocket.OPEN;
+  sent = [];
+  listeners = new Map();
+
+  constructor(url) {
+    this.url = url;
+    MockWebSocket.instances.push(this);
+    queueMicrotask(() => this.emit("open", {}));
+  }
+
+  addEventListener(type, listener) {
+    const list = this.listeners.get(type) ?? [];
+    list.push(listener);
+    this.listeners.set(type, list);
+  }
+
+  send(raw) {
+    this.sent.push(JSON.parse(raw));
+  }
+
+  close() {
+    this.emit("close", {});
+  }
+
+  emit(type, event) {
+    for (const listener of this.listeners.get(type) ?? []) listener(event);
+  }
+
+  message(message) {
+    this.emit("message", { data: JSON.stringify(message) });
+  }
+}
+window.WebSocket = MockWebSocket;
+window.ResizeObserver = class {
+  observe() {}
+  disconnect() {}
+};
+window.requestAnimationFrame = (callback) => window.setTimeout(() => callback(Date.now()), 0);
+window.cancelAnimationFrame = (handle) => window.clearTimeout(handle);
+
+const context = new Proxy(
+  {},
+  {
+    get(target, key) {
+      if (key === "measureText") return () => ({ width: 10 });
+      if (key in target) return target[key];
+      return () => undefined;
+    },
+    set(target, key, value) {
+      target[key] = value;
+      return true;
+    },
+  },
+);
+window.HTMLCanvasElement.prototype.getContext = function getContext() {
+  return context;
+};
+
+window.eval(bundle);
+
+const document = window.document;
+const byId = (id) => document.getElementById(id);
+const assert = (condition, message) => {
+  if (!condition) failures.push(message);
+};
+
+const socket = MockWebSocket.instances[0];
+assert(socket, "the app opened a WebSocket");
+assert(socket.url === "ws://127.0.0.1:8899/ws", `unexpected socket url ${socket.url}`);
+
+const hello = {
+  type: "hello",
+  version: "5.0.0",
+  grace_seconds: 60,
+  time: Date.now(),
+};
+const lobby = {
+  type: "view",
+  view: {
+    screen: "lobby",
+    connected: true,
+    user: null,
+    account: null,
+    balance: null,
+    games: [
+      ["blackjack", "Blackjack"],
+      ["crash", "Crash"],
+      ["roulette", "Roulette"],
+      ["slots", "Slots"],
+    ],
+    login_error: null,
+  },
+};
+socket.message(hello);
+socket.message(lobby);
+
+assert(byId("auth-screen").hidden === false, "auth is shown before login");
+assert(byId("session-bar").hidden === true, "no session bar before login");
+
+byId("auth-user").value = "alice";
+byId("auth-pass").value = "secret";
+byId("auth-form").dispatchEvent(new window.Event("submit", { bubbles: true, cancelable: true }));
+
+await new Promise((resolve) => setTimeout(resolve, 10));
+const login = socket.sent.find((message) => message.command?.Login);
+assert(login, "the login form sends a Login command");
+assert(login.command.Login.user === "alice", "the username is sent");
+assert(
+  /^[0-9a-f]{64}$/.test(login.command.Login.credential),
+  "the password is sent as a SHA-256 hex digest",
+);
+
+socket.message({
+  type: "view",
+  view: {
+    screen: "lobby",
+    connected: true,
+    user: "alice",
+    account: "1",
+    balance: null,
+    games: lobby.view.games,
+    login_error: null,
+  },
+});
+assert(
+  socket.sent.some((message) => message.command === "Info"),
+  "the app asks for the balance after login",
+);
+socket.message({
+  type: "view",
+  view: {
+    screen: "lobby",
+    connected: true,
+    user: "alice",
+    account: "1",
+    balance: 1000,
+    games: lobby.view.games,
+    login_error: null,
+  },
+});
+assert(byId("auth-screen").hidden === true, "auth is hidden after login");
+assert(byId("lobby-screen").hidden === false, "the lobby is shown after login");
+assert(byId("account-name").textContent === "alice", "the account name is shown");
+assert(byId("account-balance").textContent.includes("1"), "the balance is shown");
+assert(document.querySelectorAll(".game-card").length === 4, "all four game cards render");
+socket.message({
+  type: "view",
+  view: {
+    screen: "slots",
+    bet: 10,
+    balance: 1000,
+    reels: "CLOGDSCLOGDSLLO".split(""),
+    win_cells: [0, 1, 2],
+    win_lines: [1],
+    win_type: "win",
+    winnings: 20,
+    phase: "result",
+    error: null,
+  },
+});
+assert(byId("game-screen").hidden === false, "the game screen is shown");
+assert(document.querySelectorAll(".reel").length === 5, "five reels render");
+assert(document.querySelectorAll(".tile").length === 15, "fifteen tiles render");
+assert(byId("game-side").textContent.includes("SPIN"), "the slots sidebar has a spin action");
+
+socket.message({
+  type: "view",
+  view: {
+    screen: "roulette",
+    bet_amount: 10,
+    balance: 1000,
+    chip: 25,
+    bets: { chips: [{ target: { bet: "straight", number: 5 }, amount: 25 }] },
+    cursor: { Lattice: { x: 1, y: 5 } },
+    phase: "result",
+    number: 5,
+    color: "red",
+    winnings: 900,
+    error: null,
+  },
+});
+assert(document.querySelector(".roulette-canvas"), "the roulette canvas renders");
+assert(document.querySelectorAll(".chip-btn").length === 5, "the chip selector renders");
+assert(document.querySelector(".wheel-result")?.textContent.includes("5"), "the result number renders");
+
+socket.message({
+  type: "view",
+  view: {
+    screen: "blackjack",
+    status: "player",
+    balance: 990,
+    bet: 10,
+    hand: {
+      session_id: "bj1",
+      phase: "player",
+      player: ["10S", "6H"],
+      dealer: ["9D", "?"],
+      player_total: 16,
+      dealer_total: 9,
+      bet: 10,
+      base_bet: 10,
+      balance: 990,
+      actions: ["hit", "stand", "double"],
+      result: "playing",
+      winnings: 0,
+    },
+    error: null,
+  },
+});
+assert(document.querySelectorAll(".card").length === 4, "both blackjack hands render");
+assert(byId("game-side").textContent.includes("HIT"), "blackjack actions render");
+assert(byId("game-side").textContent.includes("FORFEIT") === false, "forfeit is a labelled button, not uppercase");
+assert(byId("game-side").textContent.includes("Forfeit"), "blackjack forfeit renders");
+
+socket.message({
+  type: "view",
+  view: {
+    screen: "crash",
+    status: "running",
+    balance: 990,
+    bet: 10,
+    multiplier: 1.2,
+    potential: 12,
+    crash_point: null,
+    payout: 0,
+    started_at: Date.now(),
+    commit: "ab".repeat(32),
+    seed: null,
+    error: null,
+  },
+});
+assert(document.querySelector(".crash-canvas"), "the crash canvas renders");
+assert(document.querySelector(".crash-number")?.textContent.includes("×"), "the crash multiplier renders");
+assert(byId("game-side").textContent.includes("CASH OUT"), "crash exposes cash out while running");
+assert(byId("game-side").textContent.includes("commit"), "crash shows the round commitment");
+
+socket.message({
+  type: "view",
+  view: {
+    screen: "history",
+    records: [
+      {
+        game: "slots",
+        bet: 10,
+        winnings: 20,
+        balance_after: 1010,
+        at: "2026-11-08 03:00:00",
+        details: { win_type: "win" },
+      },
+    ],
+  },
+});
+assert(byId("history-screen").hidden === false, "the history screen renders");
+assert(document.querySelector("table tbody tr"), "history rows render");
+
+socket.message({ type: "replaced" });
+assert(byId("replaced-overlay").hidden === false, "a takeover stops the old tab");
+
+await new Promise((resolve) => setTimeout(resolve, 30));
+dom.window.close();
+
+if (failures.length > 0) {
+  console.error("web smoke test failed:");
+  for (const failure of failures) console.error(`  - ${failure}`);
+  process.exit(1);
+}
+console.log("web smoke test passed");
diff --git a/web/play/tsconfig.json b/web/play/tsconfig.json
new file mode 100644
index 0000000..9814d9c
--- /dev/null
+++ b/web/play/tsconfig.json
@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "strict": true,
+    "noEmit": true,
+    "lib": ["ES2020", "DOM", "DOM.Iterable"],
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": ["src"]
+}
diff --git a/webd/Cargo.toml b/webd/Cargo.toml
new file mode 100644
index 0000000..8698404
--- /dev/null
+++ b/webd/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "zagan-bet-webd"
+version = "5.0.0"
+edition = "2024"
+license = "GPL-3.0-or-later"
+
+[dependencies]
+zagan-bet = { path = "..", default-features = false }
+tungstenite = "0.21"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+rand = "0.8"
+rusqlite = { version = "0.29", features = ["bundled"] }
diff --git a/webd/README.md b/webd/README.md
new file mode 100644
index 0000000..ac95fdb
--- /dev/null
+++ b/webd/README.md
@@ -0,0 +1,118 @@
+# `webd` — browser gateway
+
+The browser cannot open the game's TCP/TLS stream, and the rules must not be
+reimplemented in JavaScript. `webd` is a server-side frontend: one blocking
+thread per browser session, one `ClientCore`, and one ordinary client TLS
+connection to the game server. nginx terminates TLS and proxies `/ws` here.
+
+It is a workspace member like `gui/`. Its dependencies never enter the TUI,
+GUI or server build graph.
+
+## Build
+
+```sh
+cargo build -p zagan-bet-webd --release
+```
+
+## Configuration
+
+| Variable | Default | Meaning |
+| --- | --- | --- |
+| `ZAGAN_WEB_BIND` | `127.0.0.1:8890` | Loopback address nginx proxies to |
+| `ZAGAN_WEB_ORIGIN` | `https://zagan.2137697.xyz` | Exact `Origin` allowed |
+| `ZAGAN_UPSTREAM` | `127.0.0.1:11525` | Game server `host:port` |
+| `ZAGAN_UPSTREAM_FINGERPRINT` | **required** | SPKI SHA-256, 64 lowercase hex |
+| `ZAGAN_GRACE_SECONDS` | `60` | Session survives this long without a socket |
+| `ZAGAN_WEB_COOKIE_SECURE` | on for `https://` origin | `Secure` on the cookie |
+
+The fingerprint is the same one the desktop client shows:
+
+```sh
+openssl x509 -in cert.pem -pubkey -noout \
+  | openssl pkey -pubin -outform DER \
+  | sha256sum
+```
+
+There is no trust-on-first-use and no unsafe mode. A mismatch refuses to
+connect and logs both fingerprints. Run the gateway on the same host as the
+game server (or pin the remote key and accept the network hop).
+
+## systemd
+
+Install `zagan-bet-webd` under `/usr/local/bin/`, then:
+
+```ini
+# /etc/systemd/system/zagan-bet-webd.service
+[Unit]
+Description=zagan-bet browser gateway
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=zagan
+Group=zagan
+EnvironmentFile=/etc/zagan-bet-webd.env
+ExecStart=/usr/local/bin/zagan-bet-webd
+Restart=on-failure
+RestartSec=2
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=strict
+ProtectHome=true
+
+[Install]
+WantedBy=multi-user.target
+```
+
+```sh
+sudo install -m 0755 target/release/zagan-bet-webd /usr/local/bin/
+sudo install -d -m 0755 /etc
+sudo tee /etc/zagan-bet-webd.env >/dev/null <<'ENV'
+ZAGAN_UPSTREAM=127.0.0.1:11525
+ZAGAN_UPSTREAM_FINGERPRINT=<64 hex>
+ZAGAN_WEB_ORIGIN=https://zagan.2137697.xyz
+ZAGAN_WEB_BIND=127.0.0.1:8890
+ENV
+sudo systemctl daemon-reload
+sudo systemctl enable --now zagan-bet-webd
+```
+
+nginx needs:
+
+```nginx
+location = /ws {
+    proxy_pass http://127.0.0.1:8890;
+    proxy_http_version 1.1;
+    proxy_set_header Upgrade $http_upgrade;
+    proxy_set_header Connection "upgrade";
+    proxy_set_header Host $host;
+    proxy_read_timeout 3600s;
+    proxy_send_timeout 3600s;
+}
+```
+
+## Behaviour
+
+- The WebSocket handshake sets an HttpOnly, SameSite=Strict session cookie.
+  There is no credential storage in the browser or gateway.
+- A browser close starts the grace window. Upstream stays connected, crash
+  ticks are still applied to the core, and a reconnect with the same cookie
+  gets the current `View`. Expiry closes upstream; the server forfeits a live
+  hand, exactly like a desktop disconnect.
+- A second socket with the same cookie takes over: the old tab receives
+  `{"type":"replaced"}` and is closed.
+- A gateway restart loses live sessions, so their rounds are forfeited. There
+  is no protocol-level resume.
+- The browser sends `{"type":"command","command":...}` and receives
+  `view`/`notice`/`error`/`replaced`/`hello`/`pong` JSON. It never sees the
+  game wire or a certificate.
+
+## Security notes
+
+- Bind loopback. Do not expose the gateway directly.
+- Keep `ZAGAN_WEB_ORIGIN` exact. The cookie is SameSite=Strict, and the
+  `Origin` check is a second lock on cross-site WebSocket attempts.
+- The gateway is play-money only in v1. No payments, KYC or real-money copy.
+- `ZAGAN_UPSTREAM_FINGERPRINT` is the browser's credential path: a wrong or
+  missing pin must fail closed.
diff --git a/webd/src/config.rs b/webd/src/config.rs
new file mode 100644
index 0000000..d3ada8f
--- /dev/null
+++ b/webd/src/config.rs
@@ -0,0 +1,95 @@
+//! Gateway configuration from the environment.
+//!
+//! The upstream key is mandatory. There is no trust-on-first-use and no unsafe
+//! mode: the browser's credentials ride on this connection.
+
+use std::env;
+use std::time::Duration;
+
+pub const DEFAULT_BIND: &str = "127.0.0.1:8890";
+pub const DEFAULT_UPSTREAM: &str = "127.0.0.1:11525";
+pub const DEFAULT_GRACE_SECONDS: u64 = 60;
+pub const DEFAULT_ORIGIN: &str = "https://zagan.2137697.xyz";
+
+#[derive(Debug, Clone)]
+pub struct Config {
+    /// Loopback address nginx proxies `/ws` to.
+    pub bind: String,
+    /// Exact browser origin allowed on the WebSocket handshake.
+    pub origin: String,
+    /// Game server address, `host:port`.
+    pub upstream: String,
+    /// Lowercase hex SHA-256 of the upstream certificate's SPKI.
+    pub fingerprint: String,
+    /// How long a session survives without a browser socket.
+    pub grace: Duration,
+    /// `Secure` on the session cookie. Off only for local http testing.
+    pub cookie_secure: bool,
+}
+
+impl Config {
+    pub fn from_env() -> Result<Self, String> {
+        let bind = value("ZAGAN_WEB_BIND", DEFAULT_BIND);
+        let origin = value("ZAGAN_WEB_ORIGIN", DEFAULT_ORIGIN);
+        if !origin.starts_with("http://") && !origin.starts_with("https://") {
+            return Err("ZAGAN_WEB_ORIGIN must start with http:// or https://".to_string());
+        }
+        let origin = origin.trim_end_matches('/').to_string();
+
+        let upstream = value("ZAGAN_UPSTREAM", DEFAULT_UPSTREAM);
+        let fingerprint = required("ZAGAN_UPSTREAM_FINGERPRINT")?;
+        let fingerprint = fingerprint.trim().to_ascii_lowercase();
+        if fingerprint.len() != 64 || !fingerprint.bytes().all(|byte| byte.is_ascii_hexdigit()) {
+            return Err(
+                "ZAGAN_UPSTREAM_FINGERPRINT must be the 64-character SHA-256 of the upstream SPKI"
+                    .to_string(),
+            );
+        }
+
+        let grace_seconds = match env::var("ZAGAN_GRACE_SECONDS") {
+            Ok(raw) => raw
+                .trim()
+                .parse::<u64>()
+                .map_err(|_| "ZAGAN_GRACE_SECONDS must be a whole number of seconds".to_string())?,
+            Err(_) => DEFAULT_GRACE_SECONDS,
+        };
+
+        let cookie_secure = match env::var("ZAGAN_WEB_COOKIE_SECURE") {
+            Ok(raw) => matches!(
+                raw.trim().to_ascii_lowercase().as_str(),
+                "1" | "true" | "yes"
+            ),
+            Err(_) => origin.starts_with("https://"),
+        };
+
+        Ok(Self {
+            bind,
+            origin,
+            upstream,
+            fingerprint,
+            grace: Duration::from_secs(grace_seconds),
+            cookie_secure,
+        })
+    }
+}
+
+fn value(name: &str, default: &str) -> String {
+    env::var(name)
+        .ok()
+        .map(|value| value.trim().to_string())
+        .filter(|value| !value.is_empty())
+        .unwrap_or_else(|| default.to_string())
+}
+
+fn required(name: &str) -> Result<String, String> {
+    env::var(name)
+        .ok()
+        .map(|value| value.trim().to_string())
+        .filter(|value| !value.is_empty())
+        .ok_or_else(|| {
+            format!(
+                "{name} is required: the gateway pins the upstream key. \
+                 Use the SPKI fingerprint the desktop client shows."
+            )
+        })
+}
diff --git a/webd/src/main.rs b/webd/src/main.rs
new file mode 100644
index 0000000..c2cf0ff
--- /dev/null
+++ b/webd/src/main.rs
@@ -0,0 +1,61 @@
+//! Browser gateway for zagan-bet.
+//!
+//! nginx terminates TLS, serves the static app and proxies `/ws` here. This
+//! process owns one upstream TLS connection and one `ClientCore` per browser
+//! session, so the browser never speaks the game wire protocol and never sees
+//! a certificate.
+
+mod config;
+mod session;
+
+use std::net::TcpListener;
+use std::sync::Arc;
+use std::thread;
+
+use config::Config;
+
+fn main() {
+    let config = match Config::from_env() {
+        Ok(config) => config,
+        Err(error) => {
+            eprintln!("webd: {error}");
+            std::process::exit(2);
+        }
+    };
+
+    let listener = match TcpListener::bind(&config.bind) {
+        Ok(listener) => listener,
+        Err(error) => {
+            eprintln!("webd: could not bind {}: {error}", config.bind);
+            std::process::exit(1);
+        }
+    };
+
+    println!(
+        "webd listening on ws://{} for origin {}; upstream {} pinned to {}; grace {}s",
+        config.bind,
+        config.origin,
+        config.upstream,
+        config.fingerprint,
+        config.grace.as_secs()
+    );
+
+    let registry = session::new_registry();
+    for stream in listener.incoming() {
+        let stream = match stream {
+            Ok(stream) => stream,
+            Err(error) => {
+                eprintln!("webd: accept failed: {error}");
+                continue;
+            }
+        };
+        let _ = stream.set_nodelay(true);
+        let config = config.clone();
+        let registry = Arc::clone(&registry);
+        thread::spawn(move || {
+            if let Err(error) = session::accept(stream, config, registry) {
+                eprintln!("webd: {error}");
+            }
+        });
+    }
+}
diff --git a/webd/src/session.rs b/webd/src/session.rs
new file mode 100644
index 0000000..8a20721
--- /dev/null
+++ b/webd/src/session.rs
@@ -0,0 +1,623 @@
+//! One gateway session: a browser socket, one upstream TLS connection and one
+//! `ClientCore`.
+//!
+//! The browser sends `Command` JSON and renders `View` JSON. All game state,
+//! protocol framing and balance arithmetic stay in the Rust core.
+
+use std::collections::HashMap;
+use std::net::TcpStream;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{Arc, Mutex, mpsc};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use rusqlite::Connection;
+use serde::{Deserialize, Serialize};
+use tungstenite::error::Error as WsError;
+use tungstenite::http::HeaderValue;
+use tungstenite::http::header::ORIGIN;
+use tungstenite::protocol::{WebSocket, WebSocketConfig};
+use tungstenite::{Message, accept_hdr_with_config};
+
+use zagan_bet::client::core::{ClientCore, Effect};
+use zagan_bet::client::database;
+use zagan_bet::client::transport::{self, TlsStream};
+use zagan_bet::client::view::{Command, View};
+use zagan_bet::protocol::Packet;
+use zagan_bet::version::VERSION;
+
+use crate::config::Config;
+
+const COOKIE_NAME: &str = "zagan_session";
+/// On HTTPS, use the `__Host-` prefix so a sibling origin cannot set a
+/// domain-scoped cookie and fixate the session.
+const HOST_COOKIE_NAME: &str = "__Host-zagan_session";
+const REQUEST_TIMEOUT: Duration = Duration::from_secs(10);
+const POLL: Duration = Duration::from_millis(10);
+
+pub enum SocketEvent {
+    Attach(WebSocket<TcpStream>),
+}
+
+/// Session id → generation and the thread that owns it.
+///
+/// The generation lets an ending thread remove its own entry without deleting
+/// a replacement session that reused the same cookie.
+pub type Registry = Arc<Mutex<HashMap<String, (u64, mpsc::Sender<SocketEvent>)>>>;
+
+static NEXT_GENERATION: AtomicU64 = AtomicU64::new(1);
+
+pub fn new_registry() -> Registry {
+    Arc::new(Mutex::new(HashMap::new()))
+}
+
+/// Complete the WebSocket handshake, then attach this socket to an existing
+/// session or start one.
+pub fn accept(stream: TcpStream, config: Config, registry: Registry) -> Result<(), String> {
+    let mut session_id = None;
+    let origin = config.origin.clone();
+    let secure = config.cookie_secure;
+
+    let ws_config = WebSocketConfig {
+        // A command or view is a few KiB at most; keep a compromised page from
+        // making the gateway buffer tens of megabytes.
+        max_message_size: Some(64 * 1024),
+        max_frame_size: Some(64 * 1024),
+        ..WebSocketConfig::default()
+    };
+    let mut ws = accept_hdr_with_config(
+        stream,
+        |request: &tungstenite::handshake::server::Request,
+         mut response: tungstenite::handshake::server::Response| {
+            if let Some(header) = request.headers().get(ORIGIN) {
+                if header.to_str().ok() != Some(origin.as_str()) {
+                    return Err(tungstenite::http::Response::builder()
+                        .status(403)
+                        .body(Some("origin not allowed".to_string()))
+                        .expect("static response"));
+                }
+            }
+
+            let found = request
+                .headers()
+                .get("cookie")
+                .and_then(|value| value.to_str().ok())
+                .and_then(cookie_id);
+            let (id, fresh) = match found {
+                Some(id) => (id, false),
+                None => (random_id(), true),
+            };
+            if fresh {
+                let mut cookie = format!("{COOKIE_NAME}={id}; Path=/; HttpOnly; SameSite=Strict");
+                if secure {
+                    cookie.push_str("; Secure");
+                }
+                if let Ok(value) = HeaderValue::from_str(&cookie) {
+                    response.headers_mut().append("set-cookie", value);
+                }
+            }
+            session_id = Some(id);
+            Ok(response)
+        },
+        Some(ws_config),
+    )
+    .map_err(|error| format!("WebSocket handshake failed: {error}"))?;
+
+    let id = session_id.ok_or_else(|| "handshake produced no session id".to_string())?;
+    ws.get_ref()
+        .set_nonblocking(true)
+        .map_err(|error| format!("could not make the browser socket nonblocking: {error}"))?;
+
+    let (sender, receiver) = mpsc::channel();
+    let generation = NEXT_GENERATION.fetch_add(1, Ordering::Relaxed);
+    {
+        let mut sessions = registry.lock().map_err(|_| "session registry poisoned")?;
+        if let Some((_, existing)) = sessions.get(&id).cloned() {
+            match existing.send(SocketEvent::Attach(ws)) {
+                Ok(()) => return Ok(()),
+                Err(mpsc::SendError(SocketEvent::Attach(returned))) => {
+                    sessions.remove(&id);
+                    ws = returned;
+                }
+            }
+        }
+        sessions.insert(id.clone(), (generation, sender.clone()));
+    }
+
+    thread::spawn(move || {
+        let session = match Session::new(id.clone(), config) {
+            Ok(session) => Some(session),
+            Err(error) => {
+                eprintln!("[webd {id}] could not start: {error}");
+                None
+            }
+        };
+        if let Some(mut session) = session {
+            session.attach(ws);
+            session.poll_loop(&receiver);
+        }
+        if let Ok(mut sessions) = registry.lock() {
+            let own = sessions
+                .get(&id)
+                .map(|(generation_now, _)| *generation_now == generation)
+                .unwrap_or(false);
+            if own {
+                sessions.remove(&id);
+            }
+        }
+        eprintln!("[webd {id}] session ended");
+    });
+
+    Ok(())
+}
+
+fn cookie_id(raw: &str) -> Option<String> {
+    for pair in raw.split(';') {
+        let (name, value) = pair.split_once('=')?;
+        if matches!(name.trim(), COOKIE_NAME | HOST_COOKIE_NAME) {
+            let value = value.trim();
+            if value.len() == 64 && value.bytes().all(|byte| byte.is_ascii_hexdigit()) {
+                return Some(value.to_ascii_lowercase());
+            }
+            return None;
+        }
+    }
+    None
+}
+
+fn random_id() -> String {
+    use rand::RngCore;
+    let mut bytes = [0u8; 32];
+    rand::thread_rng().fill_bytes(&mut bytes);
+    bytes.iter().map(|byte| format!("{byte:02x}")).collect()
+}
+
+#[derive(Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+enum ClientMessage {
+    Command { command: Command },
+    Ping,
+}
+
+#[derive(Serialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+enum ServerMessage<'a> {
+    Hello {
+        version: &'a str,
+        grace_seconds: u64,
+        /// Signed-in user, so a refresh during a game can skip the login card.
+        user: Option<&'a str>,
+        /// Estimated game-server Unix time, milliseconds.
+        time: u64,
+    },
+    View {
+        view: &'a View,
+    },
+    Notice {
+        text: &'a str,
+    },
+    Error {
+        text: &'a str,
+    },
+    Replaced,
+    Pong,
+}
+
+struct Session {
+    id: String,
+    config: Config,
+    core: ClientCore,
+    /// In-memory trust store seeded with the pinned fingerprint. No player
+    /// credentials are ever stored here.
+    trust: Connection,
+    upstream: Option<TlsStream>,
+    ws: Option<WebSocket<TcpStream>>,
+    pending_id: Option<u64>,
+    pending_since: Option<Instant>,
+    grace_until: Option<Instant>,
+    drop_upstream: bool,
+}
+
+impl Session {
+    fn new(id: String, config: Config) -> Result<Self, String> {
+        let trust = Connection::open_in_memory()
+            .map_err(|error| format!("could not open the trust store: {error}"))?;
+        database::init_db(&trust);
+        database::save_fingerprint(&trust, &config.upstream, &config.fingerprint)
+            .map_err(|error| format!("could not pin the upstream key: {error}"))?;
+
+        Ok(Self {
+            id,
+            config,
+            core: ClientCore::new(),
+            trust,
+            upstream: None,
+            ws: None,
+            pending_id: None,
+            pending_since: None,
+            grace_until: None,
+            drop_upstream: false,
+        })
+    }
+
+    fn attach(&mut self, ws: WebSocket<TcpStream>) {
+        if let Some(mut old) = self.ws.take() {
+            send_json(&mut old, &ServerMessage::Replaced);
+            close_socket(&mut old);
+        }
+        eprintln!("[webd {}] browser attached", self.id);
+        self.ws = Some(ws);
+        self.grace_until = None;
+        let mut ws = self.ws.take().expect("just attached");
+        if let Err(text) = self.ensure_upstream() {
+            send_json(&mut ws, &ServerMessage::Error { text: &text });
+        }
+        send_json(
+            &mut ws,
+            &ServerMessage::Hello {
+                version: VERSION,
+                grace_seconds: self.config.grace.as_secs(),
+                user: self.core.user(),
+                time: self.core.server_now_ms(),
+            },
+        );
+        self.send_view(&mut ws);
+        self.ws = Some(ws);
+    }
+
+    fn poll_loop(&mut self, receiver: &mpsc::Receiver<SocketEvent>) {
+        loop {
+            match receiver.recv_timeout(POLL) {
+                Ok(SocketEvent::Attach(ws)) => self.attach(ws),
+                Err(mpsc::RecvTimeoutError::Timeout) => {}
+                Err(mpsc::RecvTimeoutError::Disconnected) => break,
+            }
+
+            self.pump_browser();
+            self.pump_upstream();
+            self.check_request_timeout();
+
+            if self.ws.is_some() {
+                self.grace_until = None;
+            } else if let Some(deadline) = self.grace_until {
+                if Instant::now() >= deadline {
+                    break;
+                }
+            } else {
+                self.grace_until = Some(Instant::now() + self.config.grace);
+            }
+        }
+
+        // Dropping the TLS stream closes upstream; the server forfeits any
+        // live hand, exactly like a desktop client disconnecting.
+        self.upstream = None;
+        eprintln!("[webd {}] grace expired", self.id);
+    }
+
+    fn pump_browser(&mut self) {
+        let Some(mut ws) = self.ws.take() else {
+            return;
+        };
+        let mut keep = true;
+
+        loop {
+            match ws.read() {
+                Ok(Message::Text(text)) => {
+                    if !self.handle_browser_text(&text, &mut ws) {
+                        keep = false;
+                        break;
+                    }
+                }
+                Ok(Message::Close(_)) => {
+                    keep = false;
+                    break;
+                }
+                Ok(Message::Ping(payload)) => {
+                    let _ = send_message(&mut ws, Message::Pong(payload));
+                }
+                Ok(Message::Binary(_)) | Ok(Message::Pong(_)) | Ok(Message::Frame(_)) => {}
+                Err(WsError::Io(error)) if error.kind() == std::io::ErrorKind::WouldBlock => break,
+                Err(WsError::ConnectionClosed) | Err(WsError::AlreadyClosed) => {
+                    keep = false;
+                    break;
+                }
+                Err(_) => {
+                    keep = false;
+                    break;
+                }
+            }
+        }
+
+        if keep {
+            self.ws = Some(ws);
+        } else {
+            self.grace_until = Some(Instant::now() + self.config.grace);
+            self.pending_id = None;
+            self.pending_since = None;
+        }
+    }
+
+    fn handle_browser_text(&mut self, text: &str, ws: &mut WebSocket<TcpStream>) -> bool {
+        let message = match serde_json::from_str::<ClientMessage>(text) {
+            Ok(message) => message,
+            Err(error) => {
+                send_json(
+                    ws,
+                    &ServerMessage::Error {
+                        text: &format!("Malformed message: {error}"),
+                    },
+                );
+                return true;
+            }
+        };
+
+        match message {
+            ClientMessage::Ping => send_json(ws, &ServerMessage::Pong),
+            ClientMessage::Command { command } => {
+                if let Err(text) = self.ensure_upstream() {
+                    send_json(ws, &ServerMessage::Error { text: &text });
+                    self.send_view(ws);
+                    return true;
+                }
+                let effects = self.core.command(command);
+                self.apply_effects(effects, Some(ws));
+            }
+        }
+        true
+    }
+
+    fn ensure_upstream(&mut self) -> Result<(), String> {
+        if self.upstream.is_some() {
+            return Ok(());
+        }
+
+        let mut trust = |_prompt: &transport::TrustPrompt| false;
+        match transport::connect(&self.config.upstream, &self.trust, false, &mut trust) {
+            Ok(connected) => {
+                self.core.set_connected(true);
+                self.core.set_server_time(connected.server_time);
+                self.core.set_host_info(
+                    Some(self.config.upstream.clone()),
+                    Some(self.config.fingerprint.clone()),
+                );
+                self.upstream = Some(connected.stream);
+                eprintln!(
+                    "[webd {}] upstream connected: {} ({}), ping {:.1}ms",
+                    self.id,
+                    self.config.upstream,
+                    connected.server_version,
+                    connected.elapsed.as_secs_f64() * 1000.0
+                );
+                Ok(())
+            }
+            Err(error) => {
+                self.core.reset_after_disconnect();
+                Err(format!("Upstream connection failed: {error}"))
+            }
+        }
+    }
+
+    fn pump_upstream(&mut self) {
+        let Some(mut upstream) = self.upstream.take() else {
+            return;
+        };
+        let mut ws = self.ws.take();
+        let mut disconnected = None;
+
+        loop {
+            match upstream.read_available_packet() {
+                Ok(Some(Packet::Event { body, .. })) => {
+                    if let Some(effects) = self.core.handle_async_line(&body) {
+                        self.apply_effects(effects, ws.as_mut());
+                    }
+                }
+                Ok(Some(Packet::Reply { id, body })) => {
+                    if self.pending_id == Some(id) {
+                        self.pending_id = None;
+                        self.pending_since = None;
+                    }
+                    let effects = self.core.handle_reply_id(id, &body);
+                    self.apply_effects(effects, ws.as_mut());
+                }
+                Ok(None) => break,
+                Err(error) => {
+                    disconnected = Some(error.to_string());
+                    break;
+                }
+            }
+        }
+
+        if self.drop_upstream {
+            self.drop_upstream = false;
+            drop(upstream);
+        } else if disconnected.is_none() {
+            self.upstream = Some(upstream);
+        }
+
+        if let Some(message) = disconnected {
+            eprintln!("[webd {}] upstream lost: {message}", self.id);
+            self.core.reset_after_disconnect();
+            self.pending_id = None;
+            self.pending_since = None;
+            if let Some(ws) = ws.as_mut() {
+                send_json(
+                    ws,
+                    &ServerMessage::Error {
+                        text: "Connection to the game server was lost",
+                    },
+                );
+                self.send_view(ws);
+            }
+        }
+
+        self.ws = ws;
+    }
+
+    fn check_request_timeout(&mut self) {
+        let Some(sent) = self.pending_since else {
+            return;
+        };
+        if sent.elapsed() < REQUEST_TIMEOUT {
+            return;
+        }
+
+        let id = self.pending_id.take();
+        self.pending_since = None;
+        self.upstream = None;
+        let mut ws = self.ws.take();
+        if let Some(id) = id {
+            let effects = self.core.handle_reply_id(id, "ERROR Request timed out");
+            self.apply_effects(effects, ws.as_mut());
+            if let Some(ws) = ws.as_mut() {
+                send_json(
+                    ws,
+                    &ServerMessage::Notice {
+                        text: "Request timed out. Disconnected.",
+                    },
+                );
+            }
+        }
+        self.core.reset_after_disconnect();
+        if let Some(ws) = ws.as_mut() {
+            self.send_view(ws);
+        }
+        self.ws = ws;
+    }
+
+    fn apply_effects(&mut self, effects: Vec<Effect>, mut ws: Option<&mut WebSocket<TcpStream>>) {
+        for effect in effects {
+            match effect {
+                Effect::Print(lines) => {
+                    // A multi-line print is a terminal table; the structured
+                    // `View` carries that data to the browser.
+                    if lines.len() == 1 {
+                        if let (Some(socket), Some(line)) = (ws.as_deref_mut(), lines.first()) {
+                            send_json(socket, &ServerMessage::Notice { text: line });
+                        }
+                    }
+                }
+                Effect::SendRequest { id, payload } => {
+                    self.pending_id = Some(id);
+                    self.pending_since = Some(Instant::now());
+                    match self.ensure_upstream() {
+                        Ok(()) => {
+                            if let Some(upstream) = self.upstream.as_mut() {
+                                if let Err(error) = upstream.write_request(id, None, &payload) {
+                                    let text = format!("Could not send request: {error}");
+                                    if let Some(socket) = ws.as_deref_mut() {
+                                        send_json(socket, &ServerMessage::Error { text: &text });
+                                    }
+                                    self.drop_upstream = true;
+                                    self.upstream = None;
+                                }
+                            }
+                        }
+                        Err(text) => {
+                            self.pending_id = None;
+                            self.pending_since = None;
+                            if let Some(socket) = ws.as_deref_mut() {
+                                send_json(socket, &ServerMessage::Error { text: &text });
+                            }
+                        }
+                    }
+                }
+                Effect::Disconnect => {
+                    self.upstream = None;
+                    self.drop_upstream = true;
+                    self.core.reset_after_disconnect();
+                }
+                Effect::Render(_) | Effect::ClearRegion | Effect::Quit => {}
+            }
+        }
+
+        if let Some(socket) = ws {
+            self.send_view(socket);
+        }
+    }
+
+    fn send_view(&self, ws: &mut WebSocket<TcpStream>) {
+        let Some(view) = self.core.view() else {
+            return;
+        };
+        send_json(ws, &ServerMessage::View { view: &view });
+    }
+}
+
+fn send_message(ws: &mut WebSocket<TcpStream>, message: Message) -> Result<(), WsError> {
+    // The read side is nonblocking; writes are small and should not fail
+    // half-way because a browser is briefly not draining its socket.
+    let _ = ws.get_ref().set_nonblocking(false);
+    let result = ws.send(message);
+    let _ = ws.get_ref().set_nonblocking(true);
+    result
+}
+
+fn send_json(ws: &mut WebSocket<TcpStream>, message: &ServerMessage<'_>) {
+    let Ok(text) = serde_json::to_string(message) else {
+        return;
+    };
+    let _ = send_message(ws, Message::Text(text));
+}
+
+fn close_socket(ws: &mut WebSocket<TcpStream>) {
+    let _ = ws.get_ref().set_nonblocking(false);
+    let _ = ws.close(None);
+    let _ = ws.get_ref().set_nonblocking(true);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use zagan_bet::client::view::{LobbyView, View};
+
+    #[test]
+    fn reads_only_well_formed_session_cookies() {
+        let id = "a".repeat(64);
+        assert_eq!(
+            cookie_id(&format!("other=1; {COOKIE_NAME}={id}; theme=dark")),
+            Some(id)
+        );
+        assert_eq!(cookie_id(&format!("{COOKIE_NAME}=short")), None);
+        assert_eq!(cookie_id("other=1"), None);
+        assert_eq!(cookie_id(""), None);
+    }
+
+    #[test]
+    fn parses_a_browser_command_and_rejects_nonsense() {
+        let message: ClientMessage = serde_json::from_str(
+            r#"{"type":"command","command":{"Login":{"user":"alice","credential":"abc"}}}"#,
+        )
+        .expect("login command");
+        match message {
+            ClientMessage::Command { command } => {
+                assert_eq!(
+                    command,
+                    Command::Login {
+                        user: "alice".to_string(),
+                        credential: "abc".to_string()
+                    }
+                );
+            }
+            _ => panic!("expected a command"),
+        }
+
+        assert!(serde_json::from_str::<ClientMessage>("{}").is_err());
+        assert!(serde_json::from_str::<ClientMessage>(r#"{"type":"nope"}"#).is_err());
+    }
+
+    #[test]
+    fn serializes_a_view_for_the_browser() {
+        let view = View::Lobby(LobbyView {
+            connected: true,
+            user: Some("alice".to_string()),
+            account: Some("1".to_string()),
+            balance: Some(1000),
+            games: vec![("slots".to_string(), "Slots".to_string())],
+            login_error: None,
+        });
+        let json = serde_json::to_string(&ServerMessage::View { view: &view }).unwrap();
+        assert!(json.contains(r#""type":"view""#));
+        assert!(json.contains(r#""screen":"lobby""#));
+        assert!(json.contains(r#""user":"alice""#));
+    }
+}