test: fill coverage gaps in lobbyService and gameService

- joinLobby: addPlayer returns falsy (race condition fallback)
- joinLobby: lobby disappears between addPlayer and final fetch
- createLobby: non-unique-violation errors re-thrown immediately
- createGameSession: unexpected DB errors propagate correctly

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

@@ -126,6 +126,14 @@ describe("createGameSession", () => {
 
     expect(mockGetDistractors).toHaveBeenCalledTimes(3);
   });
+
+  it("propagates unexpected errors from getGameTerms", async () => {
+    mockGetGameTerms.mockRejectedValue(new Error("connection refused"));
+
+    await expect(createGameSession(validRequest)).rejects.toThrow(
+      "connection refused",
+    );
+  });
 });
 
 describe("evaluateAnswer", () => {

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

@@ -87,6 +87,14 @@ describe("createLobby", () => {
       "Could not generate a unique lobby code",
     );
   });
+
+  it("re-throws non-unique-violation errors immediately", async () => {
+    const dbError = new Error("connection refused");
+    mockCreateLobby.mockRejectedValue(dbError);
+
+    await expect(createLobby("user-1")).rejects.toThrow("connection refused");
+    expect(mockCreateLobby).toHaveBeenCalledTimes(1);
+  });
 });
 
 describe("joinLobby", () => {
@@ -173,4 +181,22 @@ describe("joinLobby", () => {
       "Lobby is full",
     );
   });
+
+  it("throws ConflictError when addPlayer returns falsy (race condition)", async () => {
+    mockAddPlayer.mockResolvedValue(undefined);
+
+    await expect(joinLobby("ABC123", "user-2")).rejects.toThrow(
+      "Lobby is no longer available",
+    );
+  });
+
+  it("throws AppError when lobby disappears after addPlayer succeeds", async () => {
+    mockGetLobbyByCodeWithPlayers
+      .mockResolvedValueOnce(fakeLobbyWithPlayers)
+      .mockResolvedValueOnce(undefined);
+
+    await expect(joinLobby("ABC123", "user-2")).rejects.toThrow(
+      "Lobby disappeared during join",
+    );
+  });
 });