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/service.go

@@ -89,10 +89,11 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 		seed = svc.rng()
 	}
 	g, err := engine.New(svc.registry, engine.Options{
-		Variant: params.Variant,
-		Version: svc.version,
-		Players: len(params.Seats),
-		Seed:    seed,
+		Variant:      params.Variant,
+		Version:      svc.version,
+		Players:      len(params.Seats),
+		Seed:         seed,
+		DropoutTiles: params.DropoutTiles,
 	})
 	if err != nil {
 		if errors.Is(err, engine.ErrUnknownVariant) || errors.Is(err, engine.ErrUnknownVersion) {
@@ -114,6 +115,7 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 		turnTimeoutSecs: int(timeout / time.Second),
 		hintsAllowed:    params.HintsAllowed,
 		hintsPerPlayer:  params.HintsPerPlayer,
+		dropoutTiles:    params.DropoutTiles.String(),
 	}
 	if err := svc.store.CreateGame(ctx, ins, params.Seats); err != nil {
 		return Game{}, err
@@ -455,6 +457,22 @@ func (svc *Service) GameState(ctx context.Context, gameID, accountID uuid.UUID)
 	}, nil
 }
 
+// Participants returns the seated account IDs in seat order, the seat index whose
+// turn it is, and the game status. It is a snapshot read (no engine, no lock) that
+// lets the social package gate per-game chat and nudges without importing the
+// engine or the game's private state.
+func (svc *Service) Participants(ctx context.Context, gameID uuid.UUID) ([]uuid.UUID, int, string, error) {
+	g, err := svc.store.GetGame(ctx, gameID)
+	if err != nil {
+		return nil, 0, "", err
+	}
+	seats := make([]uuid.UUID, len(g.Seats))
+	for _, s := range g.Seats {
+		seats[s.Seat] = s.AccountID
+	}
+	return seats, g.ToMove, g.Status, nil
+}
+
 // History returns a game's full, dictionary-independent move journal.
 func (svc *Service) History(ctx context.Context, gameID uuid.UUID) (HistoryView, error) {
 	g, err := svc.store.GetGame(ctx, gameID)
@@ -506,10 +524,11 @@ func (svc *Service) replay(ctx context.Context, pre Game) (*engine.Game, error)
 		return nil, err
 	}
 	g, err := engine.New(svc.registry, engine.Options{
-		Variant: pre.Variant,
-		Version: pre.DictVersion,
-		Players: pre.Players,
-		Seed:    seed,
+		Variant:      pre.Variant,
+		Version:      pre.DictVersion,
+		Players:      pre.Players,
+		Seed:         seed,
+		DropoutTiles: pre.DropoutTiles,
 	})
 	if err != nil {
 		return nil, err

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,

backend/internal/game/types.go

@@ -60,8 +60,9 @@ type CreateParams struct {
 	Seats          []uuid.UUID
 	TurnTimeout    time.Duration // one of AllowedTurnTimeouts; zero → DefaultTurnTimeout
 	HintsAllowed   bool
-	HintsPerPlayer int   // starting per-seat hint allowance
-	Seed           int64 // zero → a random seed is chosen
+	HintsPerPlayer int                 // starting per-seat hint allowance
+	DropoutTiles   engine.DropoutTiles // disposition of a dropped-out seat's tiles (3+ players); zero → remove
+	Seed           int64               // zero → a random seed is chosen
 }
 
 // Game is the persisted state of a match: the games row joined with its seats.
@@ -76,6 +77,7 @@ type Game struct {
 	TurnTimeout    time.Duration
 	HintsAllowed   bool
 	HintsPerPlayer int
+	DropoutTiles   engine.DropoutTiles
 	MoveCount      int
 	EndReason      string // "" while active
 	Seats          []Seat