Stage 3: game domain (lifecycle, journal+cache, hint, word-check, GCG, stats)

internal/game drives the engine over a single match and owns everything the
engine does not: event-sourced persistence (a games row + an append-only decoded
move journal, with the live engine.Game kept warm in a cache and rebuilt by
replay on a miss), the play/pass/exchange/resign transitions with
validate-at-submit scoring, an unlimited score/legality preview, the hint
(per-game allowance + profile wallet), the word-check tool with complaint
capture, per-player game state, history and GCG export (Poslfit dialect), and a
background turn-timeout sweeper that auto-resigns overdue turns honouring each
player's daily away window. Like Stages 1-2 it is a service/store layer with no
HTTP; the gateway surface lands in Stage 6.

Engine: additive decoded domain API (Direction, SubmitPlay/SubmitExchange/
EvaluatePlay/HintView/Hand, MoveRecord.{Dir,MainRow,MainCol}, Registry.Lookup,
ParseVariant) so internal/game never imports scrabble-solver; and a Resign fix
so the resigner keeps their score yet never wins (the other player wins a
two-player game). Timeout reuses Resign.

Persistence: migration 00002 adds games, game_players, game_moves, complaints,
account_stats and extends accounts with away_start/away_end/hint_balance; go-jet
regenerated. account gained SpendHint. Config adds BACKEND_DICT_DIR (required),
BACKEND_DICT_VERSION, BACKEND_GAME_TIMEOUT_SWEEP_INTERVAL, BACKEND_GAME_CACHE_TTL;
main loads the registry at boot (hard dependency) and starts the sweeper.

Tests: engine resign + decoded-API tests; game unit tests (GCG, away-window
boundaries, hint budget, cache, keyed mutex, payload); inttest integration
(lifecycle, replay equivalence, timeout sweep with away grace, resign stats,
hint policy, word-check/complaint, per-game-lock). Docs (PLAN, ARCHITECTURE,
FUNCTIONAL +_ru, TESTING, README) updated.

docs/TESTING.md

@@ -22,10 +22,18 @@ tests or touching CI.
   and exchange accounting, the `Game` end-conditions (empty bag with an empty
   rack, and six scoreless turns) with end-game rack scoring, and
   **dictionary-independent history replay** (`ReplayBoard` reproduces a full
-  greedy game's final board from decoded records alone). The engine tests read
-  the DAWGs from `BACKEND_DICT_DIR` (or the sibling `scrabble-solver` checkout)
-  and fail loudly when it is absent. The 24-hour timeout / auto-resign and robot
-  balance/margin regression tests arrive with those stages.
+  greedy game's final board from decoded records alone), and the **resignation
+  win/loss rule** (the resigner keeps their score yet loses). The engine tests
+  read the DAWGs from `BACKEND_DICT_DIR` (or the sibling `scrabble-solver`
+  checkout) and fail loudly when it is absent.
+- **Game domain** *(Stage 3+)* — `backend/internal/game` adds pure unit tests
+  (the GCG writer, the away-window / effective-deadline boundaries, the hint
+  budget, the live-game cache and per-game lock, payload round-trips) plus
+  Postgres-backed integration tests in `inttest` (full lifecycle to a natural
+  end, **journal-replay equivalence**, the turn-timeout sweep with away-window
+  grace, resign win/loss and statistics, the hint allowance-then-wallet policy,
+  word-check and complaint capture, and per-game-lock serialisation). The robot
+  balance/margin regression tests arrive with Stage 5.
 
 ## Principles