fix: wire plan-gate activation and add express.json to steer/plan-gate routes

- Wire planGateRuntime.activate() into session creation path when planGate is true
  (Bug 1: sessions map stayed empty, plan/status always returned none)
- Add express.json({ limit: '1mb' }) to session-steer and plan-gate POST routes
  (Bug 2: req.body was undefined, POST with JSON body returned 400)
- Pass planGateRuntime dependency to createOpenChamberSessionService
- Add route-level and integration tests for both fixes

packages/web/server/lib/session-steer/runtime.test.js

@@ -1,5 +1,7 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { createSessionSteerRuntime } from './runtime.js';
+import express from 'express';
+import request from 'supertest';
+import { createSessionSteerRuntime, registerSessionSteerRoutes } from './runtime.js';
 
 const SESSION = 'ses_steer_test_1';
 const DIRECTORY = '/repo';
@@ -151,3 +153,41 @@ describe('session-steer runtime', () => {
     expect(openCode.state.sent.length).toBe(0);
   });
 });
+
+describe('session-steer route middleware', () => {
+  it('parses JSON body without global middleware on steer route', async () => {
+    const { state, fetchImpl } = createOpenCode();
+    state.statuses[SESSION] = { type: 'idle' };
+    state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+    const runtime = createSessionSteerRuntime({
+      globalEventHub: { subscribeEvent() { return () => {}; } },
+      buildOpenCodeUrl: (fetchPath) => `http://opencode.test${fetchPath}`,
+      getOpenCodeAuthHeaders: () => ({}),
+      broadcastGlobalUiEvent: () => {},
+      fetchImpl,
+    });
+    const app = express();
+    registerSessionSteerRoutes(app, runtime);
+    const res = await request(app)
+      .post(`/api/openchamber/session/${SESSION}/steer`)
+      .send({ directive: 'Focus on tests', mode: 'interrupt', directory: DIRECTORY })
+      .expect(202);
+    expect(res.body.accepted).toBe(true);
+    expect(state.sent.length).toBe(1);
+  });
+
+  it('returns 400 directive is required when body is missing', async () => {
+    const runtime = createSessionSteerRuntime({
+      globalEventHub: { subscribeEvent() { return () => {}; } },
+      buildOpenCodeUrl: (fetchPath) => `http://opencode.test${fetchPath}`,
+      getOpenCodeAuthHeaders: () => ({}),
+      broadcastGlobalUiEvent: () => {},
+    });
+    const app = express();
+    registerSessionSteerRoutes(app, runtime);
+    await request(app)
+      .post(`/api/openchamber/session/${SESSION}/steer`)
+      .send({ mode: 'interrupt', directory: DIRECTORY })
+      .expect(400, { error: 'directive is required' });
+  });
+});