feat(KB-648): enable parallel test execution and optimize test performance

- Enable parallel file execution in vitest configs for core, engine, CLI, and dashboard packages
- Optimize backup tests with fake timers for faster, deterministic execution
- Fix SettingsModal temporal dead zone by moving declaration before useCallback
- Fix engine tests with missing git branch delete mock and correct branch names
- Fix git worktree list mock and mission store mock in CLI tests
- Add changeset documenting test optimization patterns
- Update AGENTS.md with test optimization best practices

packages/dashboard/app/components/SettingsModal.tsx

@@ -79,6 +79,9 @@ export function SettingsModal({
   const [activeSection, setActiveSection] = useState<SectionId>(initialSection ?? SETTINGS_SECTIONS[0].id);
   const [prefixError, setPrefixError] = useState<string | null>(null);
 
+  /** Get the scope of the currently active section */
+  const activeSectionScope = SETTINGS_SECTIONS.find((s) => s.id === activeSection)?.scope;
+
   // Auth state (independent of the settings save flow)
   const [authProviders, setAuthProviders] = useState<AuthProvider[]>([]);
   const [authLoading, setAuthLoading] = useState(false);
@@ -339,9 +342,6 @@ export function SettingsModal({
     [onClose],
   );
 
-  /** Get the scope of the currently active section */
-  const activeSectionScope = SETTINGS_SECTIONS.find((s) => s.id === activeSection)?.scope;
-
   const handleSave = useCallback(async () => {
     if (prefixError || presetDraft) return;
     try {

packages/dashboard/src/routes.test.ts

@@ -33,6 +33,18 @@ function createMockGlobalSettingsStore() {
   };
 }
 
+function createMockMissionStore() {
+  return {
+    createSession: vi.fn().mockResolvedValue({ id: "session-1", status: "active" }),
+    getSession: vi.fn().mockResolvedValue({ id: "session-1", status: "active", answers: [] }),
+    updateSession: vi.fn().mockResolvedValue(undefined),
+    addAnswer: vi.fn().mockResolvedValue(undefined),
+    deleteSession: vi.fn().mockResolvedValue(undefined),
+    listSessions: vi.fn().mockResolvedValue([]),
+    generatePlan: vi.fn().mockResolvedValue({ plan: "Test plan", steps: [] }),
+  };
+}
+
 function createMockStore(overrides: Partial<TaskStore> = {}): TaskStore {
   return {
     getTask: vi.fn(),
@@ -63,6 +75,7 @@ function createMockStore(overrides: Partial<TaskStore> = {}): TaskStore {
     getWorkflowStep: vi.fn(),
     updateWorkflowStep: vi.fn(),
     deleteWorkflowStep: vi.fn(),
+    getMissionStore: vi.fn().mockReturnValue(createMockMissionStore()),
     ...overrides,
   } as unknown as TaskStore;
 }
@@ -3665,7 +3678,10 @@ describe("Git Management endpoints", () => {
   let store: TaskStore;
 
   beforeEach(() => {
-    store = createMockStore();
+    // Use the actual project root so git commands work
+    store = createMockStore({
+      getRootDir: vi.fn().mockReturnValue(process.cwd()),
+    });
   });
 
   function buildApp() {

packages/dashboard/vitest.config.ts

@@ -17,7 +17,7 @@ export default defineConfig({
     include: ["app/**/*.test.{ts,tsx}", "src/**/*.test.{ts,tsx}"],
     setupFiles: ["./vitest.setup.ts"],
     maxWorkers,
-    fileParallelism: false,
+    fileParallelism: true,
     coverage: {
       enabled: false,
       reporter: ["text", "html", "json"],