2 files changed, 80 insertions, 3 deletions

diff --git a/docs/GAMES.md b/docs/GAMES.md
index ae15d50..844d1b0 100644
--- a/docs/GAMES.md
+++ b/docs/GAMES.md
@@ -7,15 +7,52 @@
 | Slots | Done | 5 reels x 3 rows, 5 paylines, 98.6% RTP |
 | Roulette | Done | European wheel, split bets, 97.3% RTP |
 | Blackjack | Done | Six-deck shoe per hand, S17, 3:2, hit/stand/double |
+| Crash | Done | Local multiplier, server-owned clock and crash event, 99% RTP |
 
 ## Planned
 
 | Game | Shape | Main open decisions |
 | --- | --- | --- |
-| Crash | Real-time round | Crash-point distribution; cashout latency; provable fairness |
+| — | — | Provable fairness for the crash point (`hash` commit/reveal) |
+
+Crash rounds are private to one player and use the same request/response socket
+plus one server-initiated line. A shared multiplayer round would need a lobby
+and broadcast, which is a different product.
+
+## Crash
+
+- The multiplier is `exp(0.1386294 * t)`: 1.00x at the start, 2.00x at 5s,
+  10x at ~16.6s, capped at 1000x.
+- The crash point is drawn when the round starts:
+  `max(1.0, (1 - 0.01) / (1 - u))` for a uniform `u`. That gives
+  `P(crash >= m) = 0.99 / m`, so a fixed-target cashout returns 99% of the
+  stake. The cap trims the RTP by a hair.
+- The crash point is **not** sent to the client until the round ends. Knowing it
+  early would let a patched client cash out at `crash - epsilon` every round.
+- The client draws the multiplier from its own monotonic clock, anchored when
+  `CRASH_START` arrives. That number is display only.
+- The server computes the cashout multiplier from its own clock when the
+  request arrives. The client never sends a multiplier. A cashout that arrives
+  after the crash time loses the bet.
+- Because `P(crash = 1.00x) = 1%`, an instant cashout returns the stake 99% of
+  the time and nothing 1% of the time. There is no risk-free window, which is
+  why there is no cashout lockout.
+- Payouts are `floor(bet * multiplier)` in whole PLN, so anything under 1.10x
+  on a 10 PLN bet returns 10.
+- When the crash time passes, the server pushes `CRASH_BUSTED` on the same
+  connection without being asked. The client's event loop polls for keys and
+  drains the socket every 25ms.
+- Leaving with Q or disconnecting during a round forfeits the reserved bet and
+  writes a `result = forfeit` audit row.
 
-Crash needs a timed round loop and a cashout action, so it should be its own
-protocol/loop change.
+Client controls:
+
+```
+C       cash out at the server's current multiplier
+SPACE   start the next round
++ or = / -  change the next round's bet
+Q       forfeit an active round (bet is lost), or leave when idle
+```
 
 ## Blackjack
 
@@ -92,6 +129,9 @@ plays (
 
 // blackjack
 {"player":["10S","6H","5D"],"dealer":["9D","8C"],"player_total":21,"dealer_total":17,"bet":10,"result":"win","winnings":20}
+
+// crash
+{"bet":10,"crash_point":3.0,"started_at":12.44,"phase":"cashed","result":"cashed","multiplier":2.0,"payout":20}
 ```
 
 The balance update and the `plays` insert happen in one transaction
@@ -124,3 +164,22 @@ BLACKJACK_STATE <json>
 
 `BLACKJACK_STATE` carries the player/dealer cards, totals, actions, balance,
 result and winnings. The dealer's hole card is `?` until the hand is done.
+
+Crash sends one line when the round starts, one line when it crashes (without a
+request), and answers the cashout:
+
+```
+PLAY_START crash <bet>
+CRASH_START <json>
+
+CRASH_CASHOUT <session>
+CRASH_STATE <json>
+
+CRASH_BUSTED <json>        # pushed when the crash time passes
+CRASH_FORFEIT <session>
+CRASH_STATE <json>
+```
+
+`CRASH_STATE` carries `session_id`, `phase` (`running`, `cashed`, `crashed`,
+`forfeit`), `bet`, `balance`, the current/final `multiplier`, `potential`,
+`crash_point` (null while running), `payout` and `result`.
diff --git a/docs/TESTING.md b/docs/TESTING.md
index ec5c681..3c7fa61 100644
--- a/docs/TESTING.md
+++ b/docs/TESTING.md
@@ -14,6 +14,7 @@ shared global database. Each test owns its state.
 | `tests/client_core.rs` | Client command/game flows via a headless screen applying logical effects. |
 | `tests/client_ui.rs` | Help, history, completion, bet parsing, display width, cursor math. |
 | `tests/blackjack.rs` | Card totals, naturals, hit/stand/double, dealer bust, S17, state parsing. |
+| `tests/crash.rs` | Multiplier curve, payout floor, crash-point distribution, house edge, cap. |
 | `tests/protocol.rs` | Newline buffering and timeout/error classification. |
 | `tests/roulette.rs` | European wheel, split-bet payouts, zero handling, result parser. |
 | `tests/server_core.rs` | Handler, bcrypt migration, SQL injection, transaction rollback, `plays` audit, sessions. |
@@ -93,6 +94,23 @@ Use an 80-column terminal because several output lines are width-sensitive.
    double), winnings, and the final cards/result in `details`. A forfeit has
    `result = forfeit`, `winnings = 0`.
 
+## Manual crash checklist
+
+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.
+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;
+   a late cashout must never show an error over a finished round.
+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).
+
 ## Manual server checks
 
 - Register, log out, log in again (bcrypt path).