refactor(game): lock-free storage, remove /command, flatten engine wrapper

Three-stage refactor of the game-engine plumbing (game logic untouched):

Stage 1 — lock-free persistence + admin serialisation. Remove the file
lock from repo/fs (the .lock file, the Read/Write-vs-*Safe duality and the
dead ReadSafe polling) and replace the two-step rename with a single atomic
rename so concurrent reads are torn-free without a lock. Serialise the
state-mutating admin writers (init/turn/banish) with one shared router
LimitMiddleware, rewritten to block on the request context instead of a
racy shared 100ms timer.

Stage 2 — remove the obsolete immediate-command path end to end. Players
submit through PUT /api/v1/order; the legacy PUT /api/v1/command path is
deleted across game (route, handler, 24 command factories, Ctrl), backend
(Commands handler/route, engineclient.ExecuteCommands), gateway (dispatch +
executeUserGamesCommand + routing entry), the FlatBuffers/model contract
(UserGamesCommand[Response]) and transcoder, plus every affected
OpenAPI/README/FUNCTIONAL/ARCHITECTURE doc. The integration proxy test is
converted to the order path.

Stage 3 — flatten the REST->engine wrapper. Replace the executor adapter,
the controller package functions and RepoController with one concrete
controller.Service; drop the single-implementation Repo and Storage
interfaces (repo.Repo / fs.FS are now concrete). Handlers depend on a thin
handler.Engine seam and own the domain->REST projection; storage is
resolved once at startup instead of per request.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/internal/server/handlers_user_games.go

@@ -39,55 +39,6 @@ func NewUserGamesHandlers(rt *runtime.Service, engine *engineclient.Client, logg
 	return &UserGamesHandlers{runtime: rt, engine: engine, logger: logger.Named("http.user.games")}
 }
 
-// Commands handles POST /api/v1/user/games/{game_id}/commands.
-func (h *UserGamesHandlers) Commands() gin.HandlerFunc {
-	if h == nil || h.runtime == nil || h.engine == nil {
-		return handlers.NotImplemented("userGamesCommands")
-	}
-	return func(c *gin.Context) {
-		gameID, ok := parseGameIDParam(c)
-		if !ok {
-			return
-		}
-		userID, ok := userid.FromContext(c.Request.Context())
-		if !ok {
-			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "user id missing")
-			return
-		}
-		body, err := io.ReadAll(c.Request.Body)
-		if err != nil {
-			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body could not be read")
-			return
-		}
-		ctx := c.Request.Context()
-		if err := h.runtime.CheckOrdersAccept(ctx, gameID); err != nil {
-			respondGameProxyError(c, h.logger, "user games commands", ctx, err)
-			return
-		}
-		mapping, err := h.runtime.ResolvePlayerMapping(ctx, gameID, userID)
-		if err != nil {
-			respondGameProxyError(c, h.logger, "user games commands", ctx, err)
-			return
-		}
-		endpoint, err := h.runtime.EngineEndpoint(ctx, gameID)
-		if err != nil {
-			respondGameProxyError(c, h.logger, "user games commands", ctx, err)
-			return
-		}
-		payload, err := rebindActor(body, mapping.RaceName)
-		if err != nil {
-			httperr.Abort(c, http.StatusBadRequest, httperr.CodeInvalidRequest, "request body must be a JSON object")
-			return
-		}
-		resp, err := h.engine.ExecuteCommands(ctx, endpoint, payload)
-		if err != nil {
-			respondEngineProxyError(c, h.logger, "user games commands", ctx, resp, err)
-			return
-		}
-		c.Data(http.StatusOK, "application/json", resp)
-	}
-}
-
 // Orders handles POST /api/v1/user/games/{game_id}/orders.
 func (h *UserGamesHandlers) Orders() gin.HandlerFunc {
 	if h == nil || h.runtime == nil || h.engine == nil {

backend/internal/server/router.go

@@ -270,7 +270,6 @@ func registerUserRoutes(router *gin.Engine, instruments *metrics.Instruments, de
 	raceNames.POST("/register", deps.UserLobbyRaceNames.Register())
 
 	userGames := group.Group("/games")
-	userGames.POST("/:game_id/commands", deps.UserGames.Commands())
 	userGames.POST("/:game_id/orders", deps.UserGames.Orders())
 	userGames.GET("/:game_id/orders", deps.UserGames.GetOrders())
 	userGames.GET("/:game_id/reports/:turn", deps.UserGames.Report())