feat(robot): per-game display names from a wide name corpus

Decouple the displayed opponent name from the small pool of durable robot
accounts: the disguised auto-match robot now gets a freshly composed name each
game, stamped on a new game_players.display_name seat snapshot. The snapshot
also captures humans' names, freezing what an opponent sees for the life of a
game (a later rename no longer rewrites past games); readers fall back to the
account's current name for pre-migration rows.

Names come from a wide composed corpus (internal/robot/namevariety.go): Western
locales (EN/DE/ES/IT/FR/PT), native Japanese/Chinese names, a gender-agreed
Russian pool, and human-style handles. Routing keeps Pick's spirit -- a Russian
game draws Cyrillic + <=20% Latin and never a CJK script; an English game the
full corpus -- via robot.PickNamed.

Loosen account.ValidateDisplayName (and the UI mirror) to admit a trailing run
of up to five digits, so "Player2007"-style handles are valid for humans too
and the disguised robot stays indistinguishable.

Migration 00007 adds game_players.display_name (additive, NOT NULL DEFAULT '');
jet regenerated. Docs (ARCHITECTURE 7, FUNCTIONAL + _ru, PLAN, README) updated.

backend/internal/game/seatname_test.go

@@ -0,0 +1,40 @@
+package game
+
+import (
+	"context"
+	"testing"
+
+	"github.com/google/uuid"
+)
+
+// TestSeatNamesUsesSnapshot checks seatNames returns each seat's stored display-name
+// snapshot directly, without consulting the account store (svc.accounts is nil here, so
+// any lookup would be skipped or panic).
+func TestSeatNamesUsesSnapshot(t *testing.T) {
+	svc := &Service{}
+	g := Game{
+		Players: 2,
+		Seats: []Seat{
+			{Seat: 0, AccountID: uuid.New(), DisplayName: "Аня2007"},
+			{Seat: 1, AccountID: uuid.New(), DisplayName: "DarkWolf"},
+		},
+	}
+	got := svc.seatNames(context.Background(), g)
+	want := []string{"Аня2007", "DarkWolf"}
+	if len(got) != len(want) || got[0] != want[0] || got[1] != want[1] {
+		t.Fatalf("seatNames = %v, want %v", got, want)
+	}
+}
+
+// TestSeatDisplayNameFallbackEmpty checks the resolver yields "" — rather than panicking
+// — for a seat with no snapshot when no account store is available (the empty open seat
+// and pre-snapshot legacy-row paths).
+func TestSeatDisplayNameFallbackEmpty(t *testing.T) {
+	svc := &Service{}
+	if got := svc.seatDisplayName(context.Background(), Seat{Seat: 0, AccountID: uuid.New()}); got != "" {
+		t.Errorf("seatDisplayName with no snapshot and no store = %q, want empty", got)
+	}
+	if got := svc.seatDisplayName(context.Background(), Seat{Seat: 1, AccountID: uuid.Nil}); got != "" {
+		t.Errorf("empty-seat name = %q, want empty", got)
+	}
+}

backend/internal/game/service.go

@@ -179,17 +179,23 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 		}
 	}
 	seen := make(map[uuid.UUID]bool, len(params.Seats))
-	for _, id := range params.Seats {
+	seats := make([]seatInsert, len(params.Seats))
+	for i, id := range params.Seats {
 		if seen[id] {
 			return Game{}, fmt.Errorf("%w: account %s seated twice", ErrInvalidConfig, id)
 		}
 		seen[id] = true
-		if _, err := svc.accounts.GetByID(ctx, id); err != nil {
+		// Snapshot each seat's display name at creation. For a vs-AI game this stamps the
+		// robot's seeded account name (unchanged behaviour); a disguised auto-match robot
+		// instead gets a fresh per-game name when the reaper attaches it (AttachRobot).
+		acc, err := svc.accounts.GetByID(ctx, id)
+		if err != nil {
 			if errors.Is(err, account.ErrNotFound) {
 				return Game{}, fmt.Errorf("%w: account %s not found", ErrInvalidConfig, id)
 			}
 			return Game{}, err
 		}
+		seats[i] = seatInsert{accountID: id, displayName: acc.DisplayName}
 	}
 
 	seed := params.Seed
@@ -231,7 +237,7 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 		multipleWordsPerTurn: params.MultipleWordsPerTurn,
 		vsAI:                 params.VsAI,
 	}
-	if err := svc.store.CreateGame(ctx, ins, params.Seats); err != nil {
+	if err := svc.store.CreateGame(ctx, ins, seats); err != nil {
 		return Game{}, err
 	}
 	svc.cache.put(id, g, params.Variant.String())
@@ -256,7 +262,8 @@ func (svc *Service) Create(ctx context.Context, params CreateParams) (Game, erro
 // (derived from the seed): seated at seat 1, the still-empty seat 0 moves first, so the
 // caller just waits for the opponent. It backs the lobby auto-match enqueue.
 func (svc *Service) OpenOrJoin(ctx context.Context, accountID uuid.UUID, params CreateParams, openDeadline time.Time) (Game, bool, error) {
-	if _, err := svc.accounts.GetByID(ctx, accountID); err != nil {
+	acc, err := svc.accounts.GetByID(ctx, accountID)
+	if err != nil {
 		if errors.Is(err, account.ErrNotFound) {
 			return Game{}, false, fmt.Errorf("%w: account %s not found", ErrInvalidConfig, accountID)
 		}
@@ -292,13 +299,14 @@ func (svc *Service) OpenOrJoin(ctx context.Context, accountID uuid.UUID, params
 		status:               StatusOpen,
 		openDeadline:         &deadline,
 	}
-	// Seat the caller at seat 0 or seat 1 (seat 0 always moves first); the other seat
-	// is left empty (uuid.Nil) for the opponent.
-	seats := []uuid.UUID{accountID, uuid.Nil}
+	// Seat the caller at seat 0 or seat 1 (seat 0 always moves first), snapshotting their
+	// display name; the other seat is left empty (a zero seatInsert) for the opponent.
+	caller := seatInsert{accountID: accountID, displayName: acc.DisplayName}
+	seats := []seatInsert{caller, {}}
 	if seed&1 == 1 {
-		seats = []uuid.UUID{uuid.Nil, accountID}
+		seats = []seatInsert{{}, caller}
 	}
-	gameID, joined, created, err := svc.store.OpenOrJoin(ctx, accountID, ins, seats)
+	gameID, joined, created, err := svc.store.OpenOrJoin(ctx, accountID, acc.DisplayName, ins, seats)
 	if err != nil {
 		return Game{}, false, err
 	}
@@ -312,11 +320,12 @@ func (svc *Service) OpenOrJoin(ctx context.Context, accountID uuid.UUID, params
 	return g, joined, nil
 }
 
-// AttachRobot seats robotID in the empty opponent seat of open game gameID and flips
-// it to active, returning the now-active game and whether it attached (false, with a
-// zero Game, when a human joined first). It backs the matchmaking reaper.
-func (svc *Service) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID) (Game, bool, error) {
-	attached, err := svc.store.AttachRobot(ctx, gameID, robotID)
+// AttachRobot seats robotID in the empty opponent seat of open game gameID, stamping
+// displayName (the robot's fresh per-game name) on the seat, and flips it to active,
+// returning the now-active game and whether it attached (false, with a zero Game, when a
+// human joined first). It backs the matchmaking reaper.
+func (svc *Service) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID, displayName string) (Game, bool, error) {
+	attached, err := svc.store.AttachRobot(ctx, gameID, robotID, displayName)
 	if err != nil {
 		return Game{}, false, err
 	}
@@ -698,21 +707,31 @@ func (svc *Service) emitMove(ctx context.Context, post Game, rec engine.MoveReco
 	svc.pub.Publish(intents...)
 }
 
-// displayName resolves the display name of the account at the given seat, or "" when the seat
-// is absent or the lookup fails (the enriched push then falls back to its plain text).
+// seatDisplayName returns the name shown for a seat: its captured display-name snapshot
+// (docs/ARCHITECTURE.md §7), falling back to the account's current display name for a
+// pre-snapshot legacy row, or "" when neither is available.
+func (svc *Service) seatDisplayName(ctx context.Context, s Seat) string {
+	if s.DisplayName != "" {
+		return s.DisplayName
+	}
+	if svc.accounts == nil || s.AccountID == uuid.Nil {
+		return ""
+	}
+	if acc, err := svc.accounts.GetByID(ctx, s.AccountID); err == nil {
+		return acc.DisplayName
+	}
+	return ""
+}
+
+// displayName resolves the display name shown for the account at the given seat, or ""
+// when the seat is absent (the enriched push then falls back to its plain text).
 func (svc *Service) displayName(ctx context.Context, seats []Seat, seat int) string {
-	if svc.accounts == nil {
-		return ""
+	for _, s := range seats {
+		if s.Seat == seat {
+			return svc.seatDisplayName(ctx, s)
+		}
 	}
-	id, ok := seatAccount(seats, seat)
-	if !ok {
-		return ""
-	}
-	acc, err := svc.accounts.GetByID(ctx, id)
-	if err != nil {
-		return ""
-	}
-	return acc.DisplayName
+	return ""
 }
 
 // scoreLine formats the running scores with recipientSeat's score first, then the remaining
@@ -1376,15 +1395,13 @@ func (svc *Service) nonGuestSeats(ctx context.Context, seats []Seat) ([]Seat, er
 	return out, nil
 }
 
-// seatNames resolves each seat's display name for GCG export.
+// seatNames resolves each seat's display name — its captured snapshot, else the
+// account's current name (seatDisplayName) — for game state and GCG export.
 func (svc *Service) seatNames(ctx context.Context, g Game) []string {
 	names := make([]string, g.Players)
-	if svc.accounts == nil {
-		return names
-	}
 	for _, s := range g.Seats {
-		if acc, err := svc.accounts.GetByID(ctx, s.AccountID); err == nil {
-			names[s.Seat] = acc.DisplayName
+		if s.Seat >= 0 && s.Seat < len(names) {
+			names[s.Seat] = svc.seatDisplayName(ctx, s)
 		}
 	}
 	return names

backend/internal/game/store.go

@@ -108,18 +108,27 @@ type activeGame struct {
 	turnTimeoutSecs int
 }
 
+// seatInsert is one seat to create: the account to seat (uuid.Nil for the still-empty
+// opponent seat of an open auto-match game) and the display-name snapshot to stamp on
+// it — the player's name as of when the seat was taken (account.go, docs/ARCHITECTURE.md §7).
+type seatInsert struct {
+	accountID   uuid.UUID
+	displayName string
+}
+
 // CreateGame inserts the games row and one game_players row per seat (seat 0
 // first) inside a single transaction.
-func (s *Store) CreateGame(ctx context.Context, ins gameInsert, seats []uuid.UUID) error {
+func (s *Store) CreateGame(ctx context.Context, ins gameInsert, seats []seatInsert) error {
 	return withTx(ctx, s.db, func(tx *sql.Tx) error {
 		return insertGameTx(ctx, tx, ins, seats)
 	})
 }
 
 // insertGameTx inserts the games row and one game_players row per seat (seat 0
-// first) on tx. A seat whose account id is uuid.Nil is written with a NULL
-// account_id — the still-empty opponent seat of a StatusOpen auto-match game.
-func insertGameTx(ctx context.Context, tx *sql.Tx, ins gameInsert, seats []uuid.UUID) error {
+// first) on tx, stamping each seat's display-name snapshot. A seat whose account id is
+// uuid.Nil is written with a NULL account_id (and an empty snapshot) — the still-empty
+// opponent seat of a StatusOpen auto-match game.
+func insertGameTx(ctx context.Context, tx *sql.Tx, ins gameInsert, seats []seatInsert) error {
 	status := ins.status
 	if status == "" {
 		status = StatusActive
@@ -138,14 +147,14 @@ func insertGameTx(ctx context.Context, tx *sql.Tx, ins gameInsert, seats []uuid.
 	if _, err := gi.ExecContext(ctx, tx); err != nil {
 		return fmt.Errorf("insert game: %w", err)
 	}
-	for seat, accountID := range seats {
-		var acc any = accountID
-		if accountID == uuid.Nil {
+	for seat, si := range seats {
+		var acc any = si.accountID
+		if si.accountID == uuid.Nil {
 			acc = postgres.NULL
 		}
 		pi := table.GamePlayers.INSERT(
-			table.GamePlayers.GameID, table.GamePlayers.Seat, table.GamePlayers.AccountID,
-		).VALUES(ins.id, seat, acc)
+			table.GamePlayers.GameID, table.GamePlayers.Seat, table.GamePlayers.AccountID, table.GamePlayers.DisplayName,
+		).VALUES(ins.id, seat, acc, si.displayName)
 		if _, err := pi.ExecContext(ctx, tx); err != nil {
 			return fmt.Errorf("insert seat %d: %w", seat, err)
 		}
@@ -175,8 +184,10 @@ func openMatchKey(variant string, multipleWords bool) int64 {
 // used only when a game is created. A transaction-scoped advisory lock on the
 // (variant, rule) bucket serialises concurrent enqueues so two callers pair rather
 // than each opening a game. seats is the two-seat arrangement (the caller and uuid.Nil
-// for the still-empty opponent, in the chosen order) used only when a game is created.
-func (s *Store) OpenOrJoin(ctx context.Context, accountID uuid.UUID, ins gameInsert, seats []uuid.UUID) (gameID uuid.UUID, joined, created bool, err error) {
+// for the still-empty opponent, in the chosen order) used only when a game is created;
+// callerName is the caller's display-name snapshot, stamped on their seat whether they
+// open a fresh game or fill another player's open one.
+func (s *Store) OpenOrJoin(ctx context.Context, accountID uuid.UUID, callerName string, ins gameInsert, seats []seatInsert) (gameID uuid.UUID, joined, created bool, err error) {
 	err = withTx(ctx, s.db, func(tx *sql.Tx) error {
 		if _, e := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock($1)`,
 			openMatchKey(ins.variant, ins.multipleWordsPerTurn)); e != nil {
@@ -207,7 +218,7 @@ func (s *Store) OpenOrJoin(ctx context.Context, accountID uuid.UUID, ins gameIns
 			  LIMIT 1 FOR UPDATE SKIP LOCKED`,
 			ins.variant, ins.multipleWordsPerTurn, accountID).Scan(&other); {
 		case e == nil:
-			if er := fillOpenSeat(ctx, tx, other, accountID); er != nil {
+			if er := fillOpenSeat(ctx, tx, other, accountID, callerName); er != nil {
 				return er
 			}
 			gameID, joined = other, true
@@ -225,10 +236,11 @@ func (s *Store) OpenOrJoin(ctx context.Context, accountID uuid.UUID, ins gameIns
 	return gameID, joined, created, err
 }
 
-// AttachRobot fills the empty opponent seat of open game gameID with robotID and
-// flips it to active, returning whether it attached. It is a no-op (false) when the
-// game is no longer open — a human joined first — so the reaper never double-fills.
-func (s *Store) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID) (bool, error) {
+// AttachRobot fills the empty opponent seat of open game gameID with robotID, stamping
+// displayName (the robot's per-game name) on the seat, and flips it to active, returning
+// whether it attached. It is a no-op (false) when the game is no longer open — a human
+// joined first — so the reaper never double-fills.
+func (s *Store) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID, displayName string) (bool, error) {
 	attached := false
 	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
 		var status string
@@ -242,7 +254,7 @@ func (s *Store) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID) (boo
 		if status != StatusOpen {
 			return nil
 		}
-		if e := fillOpenSeat(ctx, tx, gameID, robotID); e != nil {
+		if e := fillOpenSeat(ctx, tx, gameID, robotID, displayName); e != nil {
 			return e
 		}
 		attached = true
@@ -251,12 +263,13 @@ func (s *Store) AttachRobot(ctx context.Context, gameID, robotID uuid.UUID) (boo
 	return attached, err
 }
 
-// fillOpenSeat seats accountID in an open game's empty opponent seat and flips the
-// game to active, stamping a fresh turn clock. The caller holds the game row.
-func fillOpenSeat(ctx context.Context, tx *sql.Tx, gameID, accountID uuid.UUID) error {
+// fillOpenSeat seats accountID in an open game's empty opponent seat — stamping
+// displayName as the seat's display-name snapshot — and flips the game to active with a
+// fresh turn clock. The caller holds the game row.
+func fillOpenSeat(ctx context.Context, tx *sql.Tx, gameID, accountID uuid.UUID, displayName string) error {
 	if _, err := tx.ExecContext(ctx,
-		`UPDATE backend.game_players SET account_id = $2 WHERE game_id = $1 AND account_id IS NULL`,
-		gameID, accountID); err != nil {
+		`UPDATE backend.game_players SET account_id = $2, display_name = $3 WHERE game_id = $1 AND account_id IS NULL`,
+		gameID, accountID, displayName); err != nil {
 		return fmt.Errorf("fill opponent seat: %w", err)
 	}
 	if _, err := tx.ExecContext(ctx,
@@ -1126,11 +1139,12 @@ func projectGame(g model.Games, seats []model.GamePlayers) (Game, error) {
 			accountID = *p.AccountID
 		}
 		out.Seats = append(out.Seats, Seat{
-			Seat:      int(p.Seat),
-			AccountID: accountID,
-			Score:     int(p.Score),
-			HintsUsed: int(p.HintsUsed),
-			IsWinner:  p.IsWinner,
+			Seat:        int(p.Seat),
+			AccountID:   accountID,
+			Score:       int(p.Score),
+			HintsUsed:   int(p.HintsUsed),
+			IsWinner:    p.IsWinner,
+			DisplayName: p.DisplayName,
 		})
 	}
 	return out, nil

backend/internal/game/types.go

@@ -144,6 +144,11 @@ type Seat struct {
 	Score     int
 	HintsUsed int
 	IsWinner  bool
+	// DisplayName is the seat's display-name snapshot, captured when the seat was taken
+	// (the human's then-current name, or a disguised robot's per-game name). Empty for a
+	// still-empty open seat or a pre-snapshot legacy row, where readers fall back to the
+	// account's current display name (docs/ARCHITECTURE.md §7).
+	DisplayName string
 }
 
 // OpenGame identifies an auto-match game waiting for an opponent whose robot