test: repair route harness error rendering + stop AI-checker spawning real processes in tests (#97)

* fix(test): share route error handler with test harness + fix stale assertions

The route test harness built a bare Fastify instance without the production
global error handler (server.ts), so structured errors thrown by route helpers
(findSessionOrFail → 404, parseBody → 400) fell through to Fastify's default
handler — yielding a `{statusCode,error,message}` body instead of the
`{success:false,...}` shape, and the tests asserted the old implicit-200
behavior. 51 route tests across 7 files were red.

- Extract the handler into src/web/route-error-handler.ts; server.ts and the
  test harness now install the identical handler (single source of truth).
- Correct stale assertions across route test files: throw-based error paths
  now assert 404 (unknown session) / 400 (invalid body); genuine in-handler
  `return createErrorResponse(...)` paths (200 + success:false) left untouched.
- Reformat a few test files prettier flagged (pre-existing non-compliance).

Route suite: 307/307 passing (was 256/307). No production behavior change.

* test(respawn): mock child_process so AI checker never spawns real processes

respawn-controller.test.ts drives the AI idle checker (ai-checker-base), whose
runCheck() spawns a real `tmux new-session` running `claude -p`. The AI-enabled
tests only assert the ai_checking state transition (then cancel/stop), so the
spawn produced stray real tmux sessions and claude processes on every run — the
reason `npm test` (full suite) was unsafe to run inside a managed session.

Mock node:child_process here (mirroring ai-idle-checker.test.ts), spreading the
real module so `exec` stays intact for transitively-imported modules
(tmux-manager calls promisify(exec) at load). With this, the full non-mobile
suite runs without spawning any real tmux/claude.

---------

Co-authored-by: Teigen <teigen@TeigendeMac-mini.local>

test/routes/plan-routes.test.ts

@@ -80,7 +80,7 @@ describe('plan-routes', () => {
         url: '/api/cancel-plan-generation',
         payload: { orchestratorId: 12345 }, // should be string
       });
-      expect(res.statusCode).toBe(200);
+      expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
       expect(body.success).toBe(false);
     });
@@ -129,7 +129,7 @@ describe('plan-routes', () => {
       expect(body.data.status).toBe('completed');
       expect(harness.ctx.broadcast).toHaveBeenCalledWith(
         'session:planTaskUpdate',
-        expect.objectContaining({ sessionId: harness.ctx._sessionId, taskId: 'task-1' }),
+        expect.objectContaining({ sessionId: harness.ctx._sessionId, taskId: 'task-1' })
       );
     });
 
@@ -159,7 +159,7 @@ describe('plan-routes', () => {
         url: `/api/sessions/${harness.ctx._sessionId}/plan/task/task-1`,
         payload: { status: 'invalid_status' },
       });
-      expect(res.statusCode).toBe(200);
+      expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
       expect(body.success).toBe(false);
     });
@@ -208,7 +208,7 @@ describe('plan-routes', () => {
       expect(body.data.completedCount).toBe(5);
       expect(harness.ctx.broadcast).toHaveBeenCalledWith(
         'session:planCheckpoint',
-        expect.objectContaining({ sessionId: harness.ctx._sessionId }),
+        expect.objectContaining({ sessionId: harness.ctx._sessionId })
       );
     });
   });
@@ -279,9 +279,7 @@ describe('plan-routes', () => {
     });
 
     it('rolls back to a previous version', async () => {
-      const mockPlan = [
-        { id: 'task-1', content: 'Step 1', status: 'pending' },
-      ];
+      const mockPlan = [{ id: 'task-1', content: 'Step 1', status: 'pending' }];
       harness.ctx._session.ralphTracker = {
         rollbackToVersion: vi.fn(() => ({ success: true, plan: mockPlan })),
       } as never;
@@ -296,7 +294,7 @@ describe('plan-routes', () => {
       expect(body.data).toHaveLength(1);
       expect(harness.ctx.broadcast).toHaveBeenCalledWith(
         'session:planRollback',
-        expect.objectContaining({ sessionId: harness.ctx._sessionId, version: 1 }),
+        expect.objectContaining({ sessionId: harness.ctx._sessionId, version: 1 })
       );
     });
 
@@ -358,7 +356,7 @@ describe('plan-routes', () => {
       expect(body.data.content).toBe('New task');
       expect(harness.ctx.broadcast).toHaveBeenCalledWith(
         'session:planTaskAdded',
-        expect.objectContaining({ sessionId: harness.ctx._sessionId }),
+        expect.objectContaining({ sessionId: harness.ctx._sessionId })
       );
     });
 
@@ -372,7 +370,7 @@ describe('plan-routes', () => {
         url: `/api/sessions/${harness.ctx._sessionId}/plan/task`,
         payload: { priority: 'P1' },
       });
-      expect(res.statusCode).toBe(200);
+      expect(res.statusCode).toBe(400);
       const body = JSON.parse(res.body);
       expect(body.success).toBe(false);
     });