feat: guard against empty terms in createGameSession

apps/api/src/controllers/gameController.test.ts

@@ -110,6 +110,15 @@ describe("POST /api/v1/game/start", () => {
     expect(res.status).toBe(400);
     expect(body.success).toBe(false);
   });
+
+  it("returns 404 when no terms are found for the given filters", async () => {
+    mockGetGameTerms.mockResolvedValue([]);
+
+    const res = await request(app).post("/api/v1/game/start").send(validBody);
+    const body = res.body as ErrorResponse;
+    expect(res.status).toBe(404);
+    expect(body.success).toBe(false);
+  });
 });
 
 describe("POST /api/v1/game/answer", () => {

apps/api/src/services/gameService.test.ts

@@ -273,4 +273,12 @@ describe("evaluateAnswer", () => {
       ),
     ).rejects.toThrow("Game session not found");
   });
+
+  it("throws NotFoundError when getGameTerms returns no terms", async () => {
+    mockGetGameTerms.mockResolvedValue([]);
+
+    await expect(
+      createGameSession(validRequest, store, "user-1"),
+    ).rejects.toThrow("No terms found");
+  });
 });

apps/api/src/services/gameService.ts

@@ -25,6 +25,10 @@ export const createGameSession = async (
     request.rounds,
   );
 
+  if (terms.length === 0) {
+    throw new NotFoundError("No terms found for the given filters");
+  }
+
   const answerKey = new Map<string, number>();
 
   const questions: GameQuestion[] = await Promise.all(

documentation/tickets/t00007.md

@@ -0,0 +1,41 @@
+# feat: guard against empty terms in createGameSession
+
+## Problem
+
+If `getGameTerms` returned an empty array — no vocabulary data matched the requested language, difficulty, and part of speech combination — `createGameSession` would create a session with zero questions and return it. The frontend would receive an empty `questions` array, attempt to render the first question, find nothing, and crash with no useful error message shown to the user.
+
+## Options considered
+
+### Option A — `NotFoundError` (404) ✅
+
+Throw when `terms.length === 0` before any session is created. The combination of filters yielded no data — that's a "not found" situation.
+
+Chosen because: the request is technically valid (all filter values are recognised), but the combination has no matching data. 404 is the correct semantic response.
+
+### Option B — `ValidationError` (400)
+
+Treat empty results as a bad request.
+
+Rejected because: the client sent valid input. The problem is missing data, not invalid input. 400 would be misleading.
+
+## Solution
+
+Added a guard in `createGameSession` immediately after `getGameTerms`:
+
+```ts
+if (terms.length === 0) {
+  throw new NotFoundError("No terms found for the given filters");
+}
+```
+
+The error propagates through the controller's `try/catch` to the error handler, which returns a clean 404 response. No session is created.
+
+## Files changed
+
+- `apps/api/src/services/gameService.ts` — empty terms guard added
+- `apps/api/src/services/gameService.test.ts` — pinning test added
+- `apps/api/src/controllers/gameController.test.ts` — pinning test added at HTTP layer
+
+## Commit
+
+`feat: guard against empty terms in createGameSession`