feat(KB-157): add soft-pause (enginePaused) alongside hard-stop (globalPause)

- Add enginePaused field to Settings type with soft-pause semantics (drain queue, don't kill agents)
- Gate scheduler, triage, auto-merge, and periodic merge retry on enginePaused
- Add Pause and Stop buttons to dashboard Header replacing single toggle
- Wire enginePaused state through App with optimistic toggle and unpause resume logic
- Add tests for scheduler, triage, dashboard CLI, Header, and App covering pause behavior

packages/dashboard/app/components/__tests__/Header.test.tsx

@@ -26,35 +26,91 @@ describe("Header", () => {
     expect(btn).toBeDefined();
   });
 
+  // ── Pause button (soft pause) ────────────────────────────────────
+
   it("renders pause button with 'Pause AI engine' title when not paused", () => {
-    render(<Header globalPaused={false} />);
+    render(<Header enginePaused={false} />);
     const btn = screen.getByTitle("Pause AI engine");
     expect(btn).toBeDefined();
   });
 
-  it("renders play button with 'Resume AI engine' title when paused", () => {
-    render(<Header globalPaused={true} />);
+  it("renders play button with 'Resume AI engine' title when engine is paused", () => {
+    render(<Header enginePaused={true} />);
     const btn = screen.getByTitle("Resume AI engine");
     expect(btn).toBeDefined();
   });
 
-  it("calls onToggleGlobalPause when pause button is clicked", () => {
+  it("calls onToggleEnginePause when pause button is clicked", () => {
     const onToggle = vi.fn();
-    render(<Header globalPaused={false} onToggleGlobalPause={onToggle} />);
+    render(<Header enginePaused={false} onToggleEnginePause={onToggle} />);
     const btn = screen.getByTitle("Pause AI engine");
     fireEvent.click(btn);
     expect(onToggle).toHaveBeenCalledOnce();
   });
 
-  it("applies btn-icon--paused class when paused", () => {
-    render(<Header globalPaused={true} />);
+  it("applies btn-icon--paused class when engine is paused", () => {
+    render(<Header enginePaused={true} />);
     const btn = screen.getByTitle("Resume AI engine");
     expect(btn.className).toContain("btn-icon--paused");
   });
 
-  it("does not apply btn-icon--paused class when not paused", () => {
-    render(<Header globalPaused={false} />);
+  it("does not apply btn-icon--paused class when engine is not paused", () => {
+    render(<Header enginePaused={false} />);
     const btn = screen.getByTitle("Pause AI engine");
     expect(btn.className).not.toContain("btn-icon--paused");
   });
+
+  it("pause button is disabled when globalPaused is true", () => {
+    render(<Header globalPaused={true} enginePaused={false} />);
+    const btn = screen.getByTitle("Pause AI engine");
+    expect((btn as HTMLButtonElement).disabled).toBe(true);
+  });
+
+  it("pause button is enabled when globalPaused is false", () => {
+    render(<Header globalPaused={false} enginePaused={false} />);
+    const btn = screen.getByTitle("Pause AI engine");
+    expect((btn as HTMLButtonElement).disabled).toBe(false);
+  });
+
+  // ── Stop button (hard stop) ──────────────────────────────────────
+
+  it("renders stop button with 'Stop AI engine' title when not stopped", () => {
+    render(<Header globalPaused={false} />);
+    const btn = screen.getByTitle("Stop AI engine");
+    expect(btn).toBeDefined();
+  });
+
+  it("renders play button with 'Start AI engine' title when stopped", () => {
+    render(<Header globalPaused={true} />);
+    const btn = screen.getByTitle("Start AI engine");
+    expect(btn).toBeDefined();
+  });
+
+  it("calls onToggleGlobalPause when stop button is clicked", () => {
+    const onToggle = vi.fn();
+    render(<Header globalPaused={false} onToggleGlobalPause={onToggle} />);
+    const btn = screen.getByTitle("Stop AI engine");
+    fireEvent.click(btn);
+    expect(onToggle).toHaveBeenCalledOnce();
+  });
+
+  it("applies btn-icon--stopped class when globally paused", () => {
+    render(<Header globalPaused={true} />);
+    const btn = screen.getByTitle("Start AI engine");
+    expect(btn.className).toContain("btn-icon--stopped");
+  });
+
+  it("does not apply btn-icon--stopped class when not globally paused", () => {
+    render(<Header globalPaused={false} />);
+    const btn = screen.getByTitle("Stop AI engine");
+    expect(btn.className).not.toContain("btn-icon--stopped");
+  });
+
+  it("stop button shows Play icon when globalPaused is true", () => {
+    render(<Header globalPaused={true} />);
+    const btn = screen.getByTitle("Start AI engine");
+    // The Play icon from lucide-react renders an SVG
+    const svg = btn.querySelector("svg");
+    expect(svg).toBeDefined();
+  });
 });