feat: "multiple words per turn" rule for Russian games

Add a per-game rule chosen on New Game for Russian variants (default off = the
single-word rule; on = standard Scrabble). Off, only the main word along the play
direction is validated and scored; perpendicular cross-words are ignored,
including in robot move generation. The rule rides every create and enqueue
request and joins the matchmaking key, so games and auto-match stay one uniform
path; "Russian-only" is a UI affordance (English always sends standard and shows
no toggle).

- Engine: consume scrabble-solver v1.1.0's PlayOptions{IgnoreCrossWords}, threaded
  through engine.Options.MultipleWordsPerTurn -> playOpts() into validate, score
  and generate.
- Backend: thread the flag through game CreateParams/Game + store (games column),
  lobby InvitationSettings + invitation row, and the matchmaker queue key (variant
  + rule); persisted, so a rebuilt-from-journal game keeps it. Baseline migration
  gains multiple_words_per_turn (DB not versioned); jet regenerated.
- Edge: multiple_words_per_turn added to the EnqueueRequest / CreateInvitationRequest
  FlatBuffers tables (Go + TS regenerated) and threaded through the gateway.
- UI: a "Multiple words per turn" toggle on New Game, shown for Russian variants
  only (auto-match and friend invite), default off; English silently sends standard.
- Tests: backend engine/matchmaker; UI unit (gating) + Playwright e2e (solver
  corner-case + GCG fixtures ship in v1.1.0). Docs + PRERELEASE tracker updated.

backend/internal/lobby/matchmaker_test.go

@@ -80,7 +80,7 @@ func TestMatchmakerPairsTwoHumans(t *testing.T) {
 	ctx := context.Background()
 	a, b := uuid.New(), uuid.New()
 
-	r1, err := mm.Enqueue(ctx, a, engine.VariantEnglish)
+	r1, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true)
 	if err != nil {
 		t.Fatalf("enqueue a: %v", err)
 	}
@@ -91,7 +91,7 @@ func TestMatchmakerPairsTwoHumans(t *testing.T) {
 		t.Fatalf("queue len = %d, want 1", mm.QueueLen(engine.VariantEnglish))
 	}
 
-	r2, err := mm.Enqueue(ctx, b, engine.VariantEnglish)
+	r2, err := mm.Enqueue(ctx, b, engine.VariantEnglish, true)
 	if err != nil {
 		t.Fatalf("enqueue b: %v", err)
 	}
@@ -129,10 +129,10 @@ func TestMatchmakerAlreadyQueued(t *testing.T) {
 	mm := newTestMatchmaker(&fakeCreator{}, uuid.New())
 	ctx := context.Background()
 	a := uuid.New()
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); !errors.Is(err, ErrAlreadyQueued) {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); !errors.Is(err, ErrAlreadyQueued) {
 		t.Fatalf("second enqueue err = %v, want ErrAlreadyQueued", err)
 	}
 }
@@ -141,7 +141,7 @@ func TestMatchmakerCancel(t *testing.T) {
 	mm := newTestMatchmaker(&fakeCreator{}, uuid.New())
 	ctx := context.Background()
 	a := uuid.New()
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
 	if !mm.Cancel(ctx, a) {
@@ -159,10 +159,10 @@ func TestMatchmakerVariantsAreSeparate(t *testing.T) {
 	creator := &fakeCreator{}
 	mm := newTestMatchmaker(creator, uuid.New())
 	ctx := context.Background()
-	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue en: %v", err)
 	}
-	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble); err != nil {
+	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble, true); err != nil {
 		t.Fatalf("enqueue ru: %v", err)
 	}
 	if len(creator.created) != 0 {
@@ -179,7 +179,7 @@ func TestMatchmakerFIFO(t *testing.T) {
 	ctx := context.Background()
 	a, b, c := uuid.New(), uuid.New(), uuid.New()
 	for _, id := range []uuid.UUID{a, b, c} {
-		if _, err := mm.Enqueue(ctx, id, engine.VariantEnglish); err != nil {
+		if _, err := mm.Enqueue(ctx, id, engine.VariantEnglish, true); err != nil {
 			t.Fatalf("enqueue %s: %v", id, err)
 		}
 	}
@@ -204,7 +204,7 @@ func TestMatchmakerReaperSubstitutesRobot(t *testing.T) {
 	ctx := context.Background()
 	a := uuid.New()
 
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
 
@@ -237,7 +237,7 @@ func TestMatchmakerReaperSkipsCancelled(t *testing.T) {
 	ctx := context.Background()
 	a := uuid.New()
 
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
 	mm.Cancel(ctx, a)
@@ -258,7 +258,7 @@ func TestMatchmakerCancelClearsPendingResult(t *testing.T) {
 	ctx := context.Background()
 	a := uuid.New()
 
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
 	mm.Reap(ctx, base.Add(testWaitDelay+time.Second)) // substitution stores a pending result
@@ -276,7 +276,7 @@ func TestMatchmakerReaperDefersWithoutRobot(t *testing.T) {
 	ctx := context.Background()
 	a := uuid.New()
 
-	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish); err != nil {
+	if _, err := mm.Enqueue(ctx, a, engine.VariantEnglish, true); err != nil {
 		t.Fatalf("enqueue: %v", err)
 	}
 	mm.Reap(ctx, base.Add(testWaitDelay+time.Second))
@@ -287,3 +287,57 @@ func TestMatchmakerReaperDefersWithoutRobot(t *testing.T) {
 		t.Errorf("waiter must stay queued when substitution is deferred; len %d", mm.QueueLen(engine.VariantEnglish))
 	}
 }
+
+// TestMatchmakerRulesAreSeparate confirms two players who chose the same variant but a
+// different per-turn word rule are not paired, and that the rule reaches the started game.
+func TestMatchmakerRulesAreSeparate(t *testing.T) {
+	creator := &fakeCreator{}
+	mm := newTestMatchmaker(creator, uuid.New())
+	ctx := context.Background()
+
+	// Same variant, opposite rules: they must not match.
+	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble, false); err != nil {
+		t.Fatalf("enqueue single-word: %v", err)
+	}
+	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble, true); err != nil {
+		t.Fatalf("enqueue standard: %v", err)
+	}
+	if len(creator.created) != 0 {
+		t.Fatalf("different rules must not match; created %d", len(creator.created))
+	}
+
+	// A second single-word player pairs with the first; the game carries the rule.
+	r, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble, false)
+	if err != nil {
+		t.Fatalf("enqueue single-word opponent: %v", err)
+	}
+	if !r.Matched {
+		t.Fatal("same variant and rule must match")
+	}
+	if len(creator.created) != 1 {
+		t.Fatalf("created %d games, want 1", len(creator.created))
+	}
+	if creator.created[0].MultipleWordsPerTurn {
+		t.Error("single-word match must create a game with MultipleWordsPerTurn=false")
+	}
+}
+
+// TestMatchmakerReaperKeepsRule confirms a robot substitution carries the waiter's rule.
+func TestMatchmakerReaperKeepsRule(t *testing.T) {
+	creator := &fakeCreator{}
+	mm := newTestMatchmaker(creator, uuid.New())
+	base := time.Now()
+	mm.clock = func() time.Time { return base }
+	ctx := context.Background()
+
+	if _, err := mm.Enqueue(ctx, uuid.New(), engine.VariantRussianScrabble, false); err != nil {
+		t.Fatalf("enqueue: %v", err)
+	}
+	mm.Reap(ctx, base.Add(testWaitDelay+time.Second))
+	if len(creator.created) != 1 {
+		t.Fatalf("created %d games, want 1", len(creator.created))
+	}
+	if creator.created[0].MultipleWordsPerTurn {
+		t.Error("robot substitution must keep the waiter's single-word rule")
+	}
+}