fix(dashboard): resolve default model from settings for mission interview

The mission interview route passed modelProvider/modelId from the request
body directly without resolving the configured default model from settings.
When "Use default" was selected, both values were undefined, causing
createFnAgent to use pi's internal fallback instead of the user's
configured default (e.g. zai/glm-5.1). This produced "AI returned no
valid JSON" errors.

Use resolvePlanningSettingsModel() to resolve the effective model from
the settings hierarchy (planning-specific → project → global defaults),
with explicit request overrides still taking precedence.

Closes #48

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/dashboard/src/__tests__/mission-e2e.test.ts

@@ -2878,6 +2878,163 @@ describe("Mission API", () => {
         lockedByTab: "other-tab",
       });
     });
+
+    it("POST /api/missions/interview/start resolves default model from settings when no override provided", async () => {
+      // Configure scoped store with default model settings
+      scopedStore = {
+        getRootDir: vi.fn().mockReturnValue(scopedRootDir),
+        getSettings: vi.fn().mockResolvedValue({
+          promptOverrides: {},
+          defaultProvider: "zai",
+          defaultModelId: "glm-5.1",
+        }),
+        getMissionStore: vi.fn().mockReturnValue(createMockMissionStore()),
+      } as unknown as TaskStore;
+      vi.spyOn(projectStoreResolver, "getOrCreateProjectStore").mockResolvedValue(scopedStore);
+
+      const createSpy = vi
+        .spyOn(missionInterviewModule, "createMissionInterviewSession")
+        .mockResolvedValueOnce("resolved-model-session-id");
+
+      const { app } = buildApp();
+      const res = await request(
+        app,
+        "POST",
+        `/api/missions/interview/start?projectId=${projectId}`,
+        JSON.stringify({ missionTitle: "Default Model Mission" }),
+        { "content-type": "application/json" }
+      );
+
+      expect(res.status).toBe(201);
+      // The route should resolve the default model from settings and pass it through
+      expect(createSpy).toHaveBeenCalledWith(
+        expect.any(String),
+        "Default Model Mission",
+        scopedRootDir,
+        {},
+        "zai",
+        "glm-5.1",
+      );
+    });
+
+    it("POST /api/missions/interview/start uses planning-specific model over global default", async () => {
+      // Configure scoped store with both planning-specific and global defaults
+      scopedStore = {
+        getRootDir: vi.fn().mockReturnValue(scopedRootDir),
+        getSettings: vi.fn().mockResolvedValue({
+          promptOverrides: {},
+          planningProvider: "anthropic",
+          planningModelId: "claude-sonnet-4-5",
+          defaultProvider: "zai",
+          defaultModelId: "glm-5.1",
+        }),
+        getMissionStore: vi.fn().mockReturnValue(createMockMissionStore()),
+      } as unknown as TaskStore;
+      vi.spyOn(projectStoreResolver, "getOrCreateProjectStore").mockResolvedValue(scopedStore);
+
+      const createSpy = vi
+        .spyOn(missionInterviewModule, "createMissionInterviewSession")
+        .mockResolvedValueOnce("planning-model-session-id");
+
+      const { app } = buildApp();
+      const res = await request(
+        app,
+        "POST",
+        `/api/missions/interview/start?projectId=${projectId}`,
+        JSON.stringify({ missionTitle: "Planning Model Mission" }),
+        { "content-type": "application/json" }
+      );
+
+      expect(res.status).toBe(201);
+      // Planning-specific model should take priority over global default
+      expect(createSpy).toHaveBeenCalledWith(
+        expect.any(String),
+        "Planning Model Mission",
+        scopedRootDir,
+        {},
+        "anthropic",
+        "claude-sonnet-4-5",
+      );
+    });
+
+    it("POST /api/missions/interview/start explicit model override takes precedence over settings defaults", async () => {
+      // Configure scoped store with default model settings
+      scopedStore = {
+        getRootDir: vi.fn().mockReturnValue(scopedRootDir),
+        getSettings: vi.fn().mockResolvedValue({
+          promptOverrides: {},
+          defaultProvider: "zai",
+          defaultModelId: "glm-5.1",
+        }),
+        getMissionStore: vi.fn().mockReturnValue(createMockMissionStore()),
+      } as unknown as TaskStore;
+      vi.spyOn(projectStoreResolver, "getOrCreateProjectStore").mockResolvedValue(scopedStore);
+
+      const createSpy = vi
+        .spyOn(missionInterviewModule, "createMissionInterviewSession")
+        .mockResolvedValueOnce("override-session-id");
+
+      const { app } = buildApp();
+      // Send explicit model override in request body
+      const res = await request(
+        app,
+        "POST",
+        `/api/missions/interview/start?projectId=${projectId}`,
+        JSON.stringify({
+          missionTitle: "Override Mission",
+          modelProvider: "openai",
+          modelId: "gpt-4o",
+        }),
+        { "content-type": "application/json" }
+      );
+
+      expect(res.status).toBe(201);
+      // Explicit override should win over settings defaults
+      expect(createSpy).toHaveBeenCalledWith(
+        expect.any(String),
+        "Override Mission",
+        scopedRootDir,
+        {},
+        "openai",
+        "gpt-4o",
+      );
+    });
+
+    it("POST /api/missions/interview/start passes undefined model when no defaults configured", async () => {
+      // Settings with no model configuration at all (the "no defaults" case)
+      scopedStore = {
+        getRootDir: vi.fn().mockReturnValue(scopedRootDir),
+        getSettings: vi.fn().mockResolvedValue({
+          promptOverrides: {},
+        }),
+        getMissionStore: vi.fn().mockReturnValue(createMockMissionStore()),
+      } as unknown as TaskStore;
+      vi.spyOn(projectStoreResolver, "getOrCreateProjectStore").mockResolvedValue(scopedStore);
+
+      const createSpy = vi
+        .spyOn(missionInterviewModule, "createMissionInterviewSession")
+        .mockResolvedValueOnce("no-defaults-session-id");
+
+      const { app } = buildApp();
+      const res = await request(
+        app,
+        "POST",
+        `/api/missions/interview/start?projectId=${projectId}`,
+        JSON.stringify({ missionTitle: "No Defaults Mission" }),
+        { "content-type": "application/json" }
+      );
+
+      expect(res.status).toBe(201);
+      // When no defaults are configured, provider/model should be undefined
+      expect(createSpy).toHaveBeenCalledWith(
+        expect.any(String),
+        "No Defaults Mission",
+        scopedRootDir,
+        {},
+        undefined,
+        undefined,
+      );
+    });
   });
 
   // ── Regression: Generated ID format acceptance ─────────────────────────