feat(KB-040): add break-into-subtasks toggle for task creation

- Add breakIntoSubtasks flag to core Task model and persist to store
- Plumb subtask flag through dashboard API routes with validation
- Add subtask toggle UI to inline task creation card
- Update triage agent to handle automatic subtask breakdown when enabled
- Add comprehensive tests for store, API routes, and UI components
- Include changeset for patch release documenting the new feature

packages/core/src/store.test.ts

@@ -105,6 +105,32 @@ describe("TaskStore", () => {
       expect(detail.prompt).toMatch(/^# KB-001: Add caching\n/);
       expect(detail.prompt).toContain("Implement caching layer for API responses");
     });
+
+  });
+
+  describe("breakIntoSubtasks task creation flag", () => {
+    it("persists breakIntoSubtasks=true when explicitly requested", async () => {
+      const task = await store.createTask({
+        description: "Large feature",
+        breakIntoSubtasks: true,
+      });
+
+      expect(task.breakIntoSubtasks).toBe(true);
+
+      const detail = await store.getTask(task.id);
+      expect(detail.breakIntoSubtasks).toBe(true);
+    });
+
+    it("leaves breakIntoSubtasks unset by default", async () => {
+      const task = await store.createTask({
+        description: "Regular task",
+      });
+
+      expect(task.breakIntoSubtasks).toBeUndefined();
+
+      const detail = await store.getTask(task.id);
+      expect(detail.breakIntoSubtasks).toBeUndefined();
+    });
   });
 
   // ── Lock serialization test ──────────────────────────────────────

packages/core/src/store.ts

@@ -193,6 +193,7 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
       description: input.description,
       column: input.column || "triage",
       dependencies: input.dependencies || [],
+      breakIntoSubtasks: input.breakIntoSubtasks === true ? true : undefined,
       steps: [],
       currentStep: 0,
       log: [{ timestamp: now, action: "Task created" }],

packages/core/src/types.ts

@@ -104,6 +104,8 @@ export interface Task {
   description: string;
   column: Column;
   dependencies: string[];
+  /** User-requested hint for triage: prefer splitting into child tasks when appropriate. */
+  breakIntoSubtasks?: boolean;
   worktree?: string;
   steps: TaskStep[];
   currentStep: number;
@@ -166,6 +168,7 @@ export interface TaskCreateInput {
   description: string;
   column?: Column;
   dependencies?: string[];
+  breakIntoSubtasks?: boolean;
 }
 
 export interface Settings {