feat(KB-630): inherit parent task models in subtasks

- Subtasks now inherit parent task's executor and validator model settings
- When triage creates subtasks, modelProvider/modelId and validatorModelProvider/validatorModelId are copied from parent
- Clean up legacy mission-store code (mission-store.ts, mission-types.ts, and related tests)
- Add comprehensive tests for subtask model inheritance in triage, routes, and db
- Remove obsolete changeset for missions-database-schema

packages/dashboard/src/routes.test.ts

@@ -465,6 +465,108 @@ describe("POST /subtasks/*", () => {
     expect(res.status).toBe(404);
     expect(res.body.error).toContain("not found");
   });
+
+  it("inherits parent task model settings when creating subtasks", async () => {
+    const parentTask = {
+      ...FAKE_TASK_DETAIL,
+      id: "KB-100",
+      title: "Parent Task",
+      column: "triage",
+      modelProvider: "anthropic",
+      modelId: "claude-sonnet-4-5",
+      validatorModelProvider: "openai",
+      validatorModelId: "gpt-4o",
+    };
+
+    (store.getTask as ReturnType<typeof vi.fn>).mockResolvedValue(parentTask);
+    (store.createTask as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-101", title: "First", column: "triage" })
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-102", title: "Second", column: "triage" });
+    (store.updateTask as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-101", title: "First", column: "triage", size: "S" })
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-102", title: "Second", column: "triage", size: "M" });
+
+    const start = await REQUEST(
+      buildApp(),
+      "POST",
+      "/api/subtasks/start-streaming",
+      JSON.stringify({ description: "Break this feature into subtasks" }),
+      { "Content-Type": "application/json" },
+    );
+
+    const createRes = await REQUEST(
+      buildApp(),
+      "POST",
+      "/api/subtasks/create-tasks",
+      JSON.stringify({
+        sessionId: start.body.sessionId,
+        parentTaskId: "KB-100",
+        subtasks: [
+          { tempId: "subtask-1", title: "First", description: "Do first", size: "S", dependsOn: [] },
+          { tempId: "subtask-2", title: "Second", description: "Do second", size: "M", dependsOn: ["subtask-1"] },
+        ],
+      }),
+      { "Content-Type": "application/json" },
+    );
+
+    expect(createRes.status).toBe(201);
+    expect(store.getTask).toHaveBeenCalledWith("KB-100");
+    expect(store.createTask).toHaveBeenNthCalledWith(1, expect.objectContaining({
+      title: "First",
+      modelProvider: "anthropic",
+      modelId: "claude-sonnet-4-5",
+      validatorModelProvider: "openai",
+      validatorModelId: "gpt-4o",
+    }));
+    expect(store.createTask).toHaveBeenNthCalledWith(2, expect.objectContaining({
+      title: "Second",
+      modelProvider: "anthropic",
+      modelId: "claude-sonnet-4-5",
+      validatorModelProvider: "openai",
+      validatorModelId: "gpt-4o",
+    }));
+  });
+
+  it("handles missing parent task gracefully when creating subtasks", async () => {
+    (store.getTask as ReturnType<typeof vi.fn>).mockRejectedValue(new Error("Task not found"));
+    (store.createTask as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-101", title: "First", column: "triage" });
+    (store.updateTask as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ...FAKE_TASK_DETAIL, id: "KB-101", title: "First", column: "triage", size: "S" });
+
+    const start = await REQUEST(
+      buildApp(),
+      "POST",
+      "/api/subtasks/start-streaming",
+      JSON.stringify({ description: "Break this feature into subtasks" }),
+      { "Content-Type": "application/json" },
+    );
+
+    const createRes = await REQUEST(
+      buildApp(),
+      "POST",
+      "/api/subtasks/create-tasks",
+      JSON.stringify({
+        sessionId: start.body.sessionId,
+        parentTaskId: "KB-NONEXISTENT",
+        subtasks: [
+          { tempId: "subtask-1", title: "First", description: "Do first", size: "S", dependsOn: [] },
+        ],
+      }),
+      { "Content-Type": "application/json" },
+    );
+
+    expect(createRes.status).toBe(201);
+    expect(store.getTask).toHaveBeenCalledWith("KB-NONEXISTENT");
+    // Subtask created without model inheritance (undefined values)
+    expect(store.createTask).toHaveBeenCalledWith(expect.objectContaining({
+      title: "First",
+      modelProvider: undefined,
+      modelId: undefined,
+      validatorModelProvider: undefined,
+      validatorModelId: undefined,
+    }));
+  });
 });
 
 describe("POST /tasks/:id/retry", () => {

packages/dashboard/src/routes.ts

@@ -4494,6 +4494,17 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
         return;
       }
 
+      // Fetch parent task to inherit model settings if parentTaskId is provided
+      let parentTask: Awaited<ReturnType<typeof store.getTask>> | undefined;
+      if (typeof parentTaskId === "string" && parentTaskId.trim()) {
+        try {
+          parentTask = await store.getTask(parentTaskId);
+        } catch {
+          // Parent task not found or error - proceed without inheritance
+          parentTask = undefined;
+        }
+      }
+
       const createdTasks = [] as Awaited<ReturnType<typeof store.createTask>>[];
       const tempIdToTaskId = new Map<string, string>();
 
@@ -4508,6 +4519,11 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
           description: typeof item.description === "string" ? item.description.trim() : item.title.trim(),
           column: "triage",
           dependencies: undefined,
+          // Inherit parent's model settings if available
+          modelProvider: parentTask?.modelProvider,
+          modelId: parentTask?.modelId,
+          validatorModelProvider: parentTask?.validatorModelProvider,
+          validatorModelId: parentTask?.validatorModelId,
         });
 
         tempIdToTaskId.set(item.tempId, task.id);