# Project Conventions for zagan-bet

## Type Safety
- SQLite `INTEGER` is `i64`. Never cast to `u64` without a bounds check.
- Balance, bet, and winnings fields must agree on `i64` or `u64` across the
  entire codebase — pick one and enforce it.
- Negative balance is a state the DB can represent; the application must reject
  plays that would produce one, not silently wrap via `as u64`.

## Game Logic
- Never compute the same payout/result in two places. `process_action` and
  `calculate_result` must not both independently derive winnings.
  The canonical split: `process_action` mutates state and stores raw data
  (reels, win_type); `calculate_result` reads that data and produces the
  `GameResult`. One path, one formula.
- When checking symmetry (e.g. two-of-a-kind), enumerate **all** pairs, not
  just adjacent indices. `[a, b, a]` is a valid match.

## Session Tracking
- Every `PLAY_START` must produce a session entry before the balance is
  touched. The session is the audit trail for the deduction; without it the
  deduction is orphaned.
- Multi-step games (blackjack, crash) reserve with `database::reserve_play`:
  the debit and the `pending_plays` row are one transaction. Settlement deletes
  that row and writes the `plays` row in the same transaction.
- Sweep orphaned reservations only at startup (`recover_orphaned_reservations`),
  never per connection. A per-connection sweep would settle another player's
  live hand. An orphaned reservation is a forfeit, never a refund.
- Clean up sessions on client disconnect. If a game is in progress when the
  connection drops, settle it as a forfeit (the reserved bet is lost) and
  record the play; never refund an active hand.

## Server Handler
- Never hold a lock, drop it, then re-acquire it in the same function to
  mutate the same resource. Acquire once, scope the lock to the operation.
- All balance mutations (`SET balance = balance ± ?`) must happen in a
  transaction.

## Crash
- 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
  state and contains no I/O or terminal types.
- The command-line editor and key mapping live in `client::input`. The core
  receives `Command` or a finished line through `submit_line`, never a key.
- egui lives in the `gui/` workspace member. Its dependencies must never
  enter the TUI or server build graph: no GUI crate in the root package's
  `[dependencies]`. The GUI may depend on the core, never the reverse.
- Build the GUI with `cargo build -p zagan-bet-gui --profile gui-release`;
  the profile lives at the workspace root because a member's is ignored.
- Colours, spacing and font sizes come from `gui/src/theme.rs`; screens must
  not hard-code them. The embedded fonts are Open Sans (OFL) and Hack (MIT);
  ship their licence files with any change.
- GUI integration tests live in `gui/tests/`, because the root package cannot
  depend on the GUI.
- First contact shows the fingerprint and waits for a decision before sending
  any credentials. A changed key is a hard stop; forgetting it is explicit.
- The GUI is themed deliberately. Default egui styling is not an acceptable
  look; keep a style module and a reference screen. The palette is derived
  from the terminal's ANSI colours, and felt green is only ever the roulette
  table.
- The GUI felt is pointer-first: the hover snaps to the shared fine lattice
  (cell centre, edge, crossing), left click adds the chip and right or middle
  click takes one back. The terminal keeps its arrow-key cursor; the GUI does
  not paint it.
- The GUI network worker (`gui/src/net.rs`) owns the TLS stream and the request
  deadline; `ClientCore` stays I/O-free. One thread with channels, no async
  runtime.
- Game sidebars pin their action block with `widgets::sidebar_layout`. An
  action that moves as the bet slip grows is a bug.
- The embedded fonts have no suit or arrow glyphs. Draw card suits as shapes
  and use plain words for navigation; a glyph that is not in Open Sans or Hack
  renders as tofu.
- `scripts/publish.sh` builds the GUI with `gui-release`; the installers are
  stable site files (`web/install.sh`, `web/install.ps1`) that read
  `web/latest.php` for the newest build and its SHA-256. Never regenerate or
  version the installers per release, install system-wide, or skip the hash
  check. The Windows installer waits for Enter before closing; `-NoPause` is
  only for automation.
- Windows renders through wgpu on Direct3D 12, including the WARP software
  adapter, so a machine with only OpenGL 1.1 (VM, Remote Desktop) still runs.
  Linux keeps the smaller glow renderer. Do not assume OpenGL 2.0 on Windows.
- The download page links the public git repository
  (https://git.2137697.xyz/zagan-bet) for the GPL corresponding source.
  Run publish from a clean tree so the linked history matches the binaries.

## Client TUI
- `render_lines()` and `render()` must agree. If `render()` uses `\r\n`,
  count lines against the same string the cursor will erase.
  Prefer returning a fixed known count for the game's static layout and
  letting dynamic content fill it, rather than inferring the count.
- The client refuses to start below 80x24 (`terminal_too_small`). Every game
  board must fit in that size; a new board wider or taller than the minimum
  must raise the minimum in the same change.
- A resize below the minimum warns, but never during a live round
  (`ClientCore::is_live_game`): a reserved bet must be finishable.

## Schema
- The app is in alpha: do not write schema migrations. `init_db` creates the
  current shape; a schema change means deleting `server.db` and `client.db`.
  Files written by an older build are not supported.

## Error Paths
- When a game action fails after a balance deduction, the refund must happen
  in the same transaction scope as the deduction, not as a separate
  `execute()` call.
- Never silently ignore `Err` on balance mutations. If the refund fails,
  log the username, balance, and operation; surface to the operator.

## Tests
- Every `calculate_payout` / `calculate_result` edge case gets a unit test
  in `tests/`. Tests that exercise game logic use a deterministic seed or
  a test helper that calls the function directly, not the network.
- A change to game logic that breaks an existing payout pattern must fail
  a test before it reaches the server.

## TLS / TOFU
- See `src/tofu.rs` for the trust model. The fingerprint is over the
  certificate's SPKI, not the whole certificate.
- Credentials are keyed by the SPKI fingerprint, not by address: one login
  covers every address that presents the same key. Never look credentials up
  by host.
- `forget_host` removes one address. Drop the credential only when no address
  with that fingerprint remains, or two addresses for one server would stop
  sharing a login. `forget-login` is the narrower action: it drops the
  credential and keeps the pinned key.
- `save_host` must not wipe the fingerprint column. Use `ON CONFLICT ...
  DO UPDATE SET last_used` — never `INSERT OR REPLACE`.
- The client transport lives in `client::transport`. It records the key during
  the handshake, then asks the frontend (`TrustPrompt`) before sending `HELLO`
  or credentials. A changed key is a hard error, and forgetting it is explicit.

## Versioning

Use semantic versioning (`MAJOR.MINOR.PATCH`) in `Cargo.toml`.

- **MAJOR** — breaking protocol changes (wire format, TLS trust model,
  database schema migration that can't auto-upgrade).
- **MINOR** — new features, new game types, new commands, or any change to
  shared semantics.
- **PATCH** — bug fixes, payout corrections, refactors that don't change
  observable behavior.

Client and server are **MAJOR.MINOR lockstep**: they may differ only in the
patch component. `HELLO <version>` is the first line after TLS; the server
refuses a mismatch before any credentials are sent. A feature that changes
the wire format is a MAJOR bump and a simultaneous release of both sides, not
a compatible MINOR.

Bump the version in `Cargo.toml` as the **last** step before committing
a release-worthy change. The commit message should contain the new version
number (e.g. `v0.2.0`).