Stage 4: lobby & social (matchmaking, friends, blocks, chat+nudge, invitations, profile, email, multi-player drop-out)

Engine: multi-player drop-out-and-continue with a per-game tile disposition (remove default / return), resigned seats skipped and excluded from the win, leaver rack never revealed; 2-player behaviour unchanged.

New domains (service/store, no HTTP yet): internal/social (friend request/accept graph, per-user blocks, per-game chat with nudge as a message kind, content filter via mvdan.cc/xurls/v2 + leet/separator normaliser + phone heuristic) and internal/lobby (in-memory variant-keyed matchmaking pool, friend-game invitations invite->accept with lazy 7-day expiry). account gains profile editing and the email confirm-code flow (Mailer seam: SMTP or log mailer).

Migration 00003_social.sql + regenerated jet. main wires the new services into the server (accessors for the Stage 6 handlers); robot substitution stays in Stage 5, REST/stream/push in Stage 6/8. Docs (PLAN, ARCHITECTURE, FUNCTIONAL+ru, TESTING, README) updated.

backend/internal/game/store.go

@@ -37,6 +37,7 @@ type gameInsert struct {
 	turnTimeoutSecs int
 	hintsAllowed    bool
 	hintsPerPlayer  int
+	dropoutTiles    string
 }
 
 // statDelta is one account's contribution to its statistics on a game finish.
@@ -91,7 +92,8 @@ func (s *Store) CreateGame(ctx context.Context, ins gameInsert, seats []uuid.UUI
 		gi := table.Games.INSERT(
 			table.Games.GameID, table.Games.Variant, table.Games.DictVersion, table.Games.Seed,
 			table.Games.Players, table.Games.TurnTimeoutSecs, table.Games.HintsAllowed, table.Games.HintsPerPlayer,
-		).VALUES(ins.id, ins.variant, ins.dictVersion, ins.seed, ins.players, ins.turnTimeoutSecs, ins.hintsAllowed, ins.hintsPerPlayer)
+			table.Games.DropoutTiles,
+		).VALUES(ins.id, ins.variant, ins.dictVersion, ins.seed, ins.players, ins.turnTimeoutSecs, ins.hintsAllowed, ins.hintsPerPlayer, ins.dropoutTiles)
 		if _, err := gi.ExecContext(ctx, tx); err != nil {
 			return fmt.Errorf("insert game: %w", err)
 		}
@@ -367,6 +369,10 @@ func projectGame(g model.Games, seats []model.GamePlayers) (Game, error) {
 	if err != nil {
 		return Game{}, fmt.Errorf("game: %s: %w", g.GameID, err)
 	}
+	dropout, err := engine.ParseDropoutTiles(g.DropoutTiles)
+	if err != nil {
+		return Game{}, fmt.Errorf("game: %s: %w", g.GameID, err)
+	}
 	out := Game{
 		ID:             g.GameID,
 		Variant:        variant,
@@ -378,6 +384,7 @@ func projectGame(g model.Games, seats []model.GamePlayers) (Game, error) {
 		TurnTimeout:    time.Duration(g.TurnTimeoutSecs) * time.Second,
 		HintsAllowed:   g.HintsAllowed,
 		HintsPerPlayer: int(g.HintsPerPlayer),
+		DropoutTiles:   dropout,
 		MoveCount:      int(g.MoveCount),
 		CreatedAt:      g.CreatedAt,
 		UpdatedAt:      g.UpdatedAt,