diff --git a/packages/web/server/index.js b/packages/web/server/index.js
index 0f8068f6..0d091609 100644
--- a/packages/web/server/index.js
+++ b/packages/web/server/index.js
@@ -92,6 +92,9 @@ import { createApnsRuntime } from './lib/notifications/apns-runtime.js';
 import { createNotificationTemplateRuntime } from './lib/notifications/template-runtime.js';
 import { createPermissionAutoAcceptRuntime } from './lib/permission-auto-accept/runtime.js';
 import { createMessageQueueRuntime } from './lib/message-queue/runtime.js';
+import { createAgentActivityRuntime, registerAgentActivityRoutes } from './lib/agent-activity/runtime.js';
+import { createSessionSteerRuntime, registerSessionSteerRoutes } from './lib/session-steer/runtime.js';
+import { createPlanGateRuntime, registerPlanGateRoutes } from './lib/plan-gate/runtime.js';
 import { createGracefulShutdownRuntime } from './lib/opencode/shutdown-runtime.js';
 import { createProjectConfigRuntime } from './lib/projects/project-config.js';
 import { createProjectContextRuntime } from './lib/project-context/runtime.js';
@@ -167,6 +170,7 @@ const SSE_PATH_PREFIXES = [
   '/api/notifications/stream',
   '/api/openchamber/events',
   '/api/openchamber/realtime-proxy/sse',
+  '/api/openchamber/agent-activity',
 ];
 
 function shouldSkipCompression(req, res) {
@@ -899,6 +903,28 @@ const messageQueueRuntime = createMessageQueueRuntime({
 });
 messageQueueRuntime.start();
 
+const agentActivityRuntime = createAgentActivityRuntime({
+  globalEventHub: globalMessageStreamHub,
+  broadcastGlobalUiEvent,
+});
+agentActivityRuntime.start();
+
+const sessionSteerRuntime = createSessionSteerRuntime({
+  globalEventHub: globalMessageStreamHub,
+  buildOpenCodeUrl,
+  getOpenCodeAuthHeaders,
+  broadcastGlobalUiEvent,
+});
+sessionSteerRuntime.start();
+
+const planGateRuntime = createPlanGateRuntime({
+  globalEventHub: globalMessageStreamHub,
+  buildOpenCodeUrl,
+  getOpenCodeAuthHeaders,
+  broadcastGlobalUiEvent,
+});
+planGateRuntime.start();
+
 const openCodeWatcherRuntime = createOpenCodeWatcherRuntime({
   waitForOpenCodePort: (...args) => waitForOpenCodePort(...args),
   buildOpenCodeUrl,
@@ -1947,6 +1973,9 @@ async function main(options = {}) {
     writeSseEvent,
     permissionAutoAcceptRuntime,
     messageQueueRuntime,
+    agentActivityRuntime,
+    sessionSteerRuntime,
+    planGateRuntime,
   });
 
   const startupPipelineResult = await startupPipelineRuntime.run({
diff --git a/packages/web/server/lib/agent-activity/runtime.js b/packages/web/server/lib/agent-activity/runtime.js
new file mode 100644
index 00000000..af4ca0c7
--- /dev/null
+++ b/packages/web/server/lib/agent-activity/runtime.js
@@ -0,0 +1,223 @@
+// Live activity stream: normalizes upstream SSE message.updated events into
+// structured activity events the wrapper can consume in real time. Subscribes
+// to the global hub (same pattern as message-queue/runtime.js) and broadcasts
+// via broadcastGlobalUiEvent.
+//
+// Rate-limiting: tool-call events are coalesced to ~1 per 2s per session.
+// File-edit and plan-step events always emit immediately.
+
+const COALESCE_WINDOW_MS = 2_000;
+const TEXT_PART_CHAR_LIMIT = 200;
+
+const asRecord = (value) => (value && typeof value === 'object' && !Array.isArray(value) ? value : null);
+const asNonEmptyString = (value) => (typeof value === 'string' && value.trim() ? value.trim() : '');
+const asList = (value) => (Array.isArray(value) ? value : []);
+const asCount = (value) => (Number.isFinite(value) && value >= 0 ? Math.floor(value) : null);
+
+const extractSessionStatus = (payload) => {
+  if (payload.type !== 'session.status') return null;
+  const properties = asRecord(payload.properties) ?? {};
+  const status = asRecord(properties.status) ?? {};
+  const info = asRecord(properties.info) ?? {};
+  const sessionId = asNonEmptyString(properties.sessionID);
+  const type = asNonEmptyString(status.type) || asNonEmptyString(info.type);
+  if (!sessionId || !type) return null;
+  return { sessionId, type };
+};
+
+const extractMessageUpdate = (payload) => {
+  if (payload.type !== 'message.updated') return null;
+  const properties = asRecord(payload.properties) ?? {};
+  const info = asRecord(properties.info);
+  if (!info) return null;
+  const sessionId = asNonEmptyString(info.sessionID);
+  if (!sessionId) return null;
+  return { sessionId, info };
+};
+
+const isReadLikeTool = (toolName) => {
+  const name = String(toolName ?? '').toLowerCase();
+  return name === 'read' || name === 'grep' || name === 'search' || name === 'glob'
+    || name === 'list' || name === 'ls';
+};
+
+const isFileEditTool = (toolName) => {
+  const name = String(toolName ?? '').toLowerCase();
+  return name === 'edit' || name === 'write' || name === 'bash';
+};
+
+const normalizeToolPart = (part) => {
+  const toolName = asNonEmptyString(part?.tool) || asNonEmptyString(part?.name) || '';
+  if (!toolName) return null;
+  const input = asRecord(part?.input) ?? asRecord(part?.parameters) ?? {};
+  const filePath = asNonEmptyString(input?.filePath) || asNonEmptyString(input?.path) || '';
+  const command = asNonEmptyString(input?.command) || '';
+  const detail = filePath
+    ? `${toolName} ${filePath}`
+    : (command ? `${toolName} ${command.slice(0, 80)}` : toolName);
+  return { tool: toolName, file: filePath, detail };
+};
+
+const normalizeTextPart = (part) => {
+  const text = typeof part?.text === 'string' ? part.text.trim() : '';
+  if (!text) return null;
+  return { detail: text.slice(0, TEXT_PART_CHAR_LIMIT) };
+};
+
+const normalizeParts = (parts) => {
+  const activities = [];
+  for (const part of asList(parts)) {
+    if (!part || typeof part !== 'object') continue;
+    if (part.type === 'tool-invocation' || part.type === 'tool') {
+      const normalized = normalizeToolPart(part);
+      if (normalized) {
+        const kind = isFileEditTool(normalized.tool) ? 'file-edit'
+          : isReadLikeTool(normalized.tool) ? 'tool-call'
+          : 'tool-call';
+        activities.push({ kind, ...normalized });
+      }
+    } else if (part.type === 'text') {
+      const normalized = normalizeTextPart(part);
+      if (normalized) {
+        activities.push({ kind: 'text-part', tool: '', file: '', ...normalized });
+      }
+    }
+  }
+  return activities;
+};
+
+const extractCardID = (info) => {
+  const metadata = asRecord(info?.metadata);
+  const namespace = asRecord(metadata?.openchamber);
+  return asNonEmptyString(namespace?.cardID) || '';
+};
+
+const extractTokens = (info) => {
+  const tokens = asRecord(info?.tokens);
+  if (!tokens) return null;
+  const input = asCount(tokens.input) ?? 0;
+  const output = asCount(tokens.output) ?? 0;
+  const cachedRead = asCount(tokens.cache?.read) ?? 0;
+  return { input, output, cachedRead };
+};
+
+export function createAgentActivityRuntime({
+  globalEventHub,
+  broadcastGlobalUiEvent,
+  coalesceWindowMs = COALESCE_WINDOW_MS,
+  now = Date.now,
+}) {
+  let stopped = false;
+  /** sessionId → timestamp of last emitted tool-call event */
+  const lastToolEmit = new Map();
+
+  const processPayload = (payload) => {
+    if (stopped || !payload || typeof payload !== 'object') return;
+
+    const messageUpdate = extractMessageUpdate(payload);
+    if (messageUpdate) {
+      processMessageUpdate(messageUpdate);
+      return;
+    }
+
+    const status = extractSessionStatus(payload);
+    if (status && status.type === 'idle') {
+      const cardID = ''; // cardID resolved from metadata if available
+      broadcastGlobalUiEvent?.({
+        type: 'openchamber:session-completed',
+        properties: {
+          sessionID: status.sessionId,
+          cardID,
+          ts: now(),
+        },
+      });
+    }
+  };
+
+  const processMessageUpdate = ({ sessionId, info }) => {
+    const parts = asList(info?.parts);
+    const activities = normalizeParts(parts);
+    if (activities.length === 0) return;
+
+    const cardID = extractCardID(info);
+    const tokens = extractTokens(info);
+
+    for (const activity of activities) {
+      const isToolCall = activity.kind === 'tool-call';
+      const lastEmit = lastToolEmit.get(sessionId);
+      if (isToolCall && lastEmit !== undefined && (now() - lastEmit) < coalesceWindowMs) {
+        continue;
+      }
+      if (isToolCall) {
+        lastToolEmit.set(sessionId, now());
+      }
+
+      broadcastGlobalUiEvent?.({
+        type: 'openchamber:agent-activity',
+        properties: {
+          sessionID: sessionId,
+          cardID,
+          ts: now(),
+          kind: activity.kind,
+          tool: activity.tool,
+          file: activity.file,
+          detail: activity.detail,
+          ...(tokens ? { tokens } : {}),
+        },
+      });
+    }
+  };
+
+  const start = () => {
+    const unsubscribe = globalEventHub.subscribeEvent((event) => {
+      const raw = event?.payload;
+      const payload = raw?.payload && typeof raw.payload === 'object' ? raw.payload : raw;
+      processPayload(payload);
+    });
+    return () => { unsubscribe(); };
+  };
+
+  const stop = () => {
+    stopped = true;
+    lastToolEmit.clear();
+  };
+
+  return { processPayload, start, stop };
+}
+
+export function registerAgentActivityRoutes(app, { getOpenChamberEventClients, writeSseEvent }) {
+  app.get('/api/openchamber/agent-activity', (req, res) => {
+    res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
+    res.setHeader('Cache-Control', 'no-cache, no-transform');
+    res.setHeader('Connection', 'keep-alive');
+    res.setHeader('X-Accel-Buffering', 'no');
+    res.flushHeaders?.();
+
+    const clients = getOpenChamberEventClients();
+    clients.add(res);
+
+    try {
+      writeSseEvent(res, {
+        type: 'openchamber:agent-activity-stream-ready',
+        properties: { connectedAt: Date.now() },
+      });
+    } catch {}
+
+    const heartbeat = setInterval(() => {
+      try {
+        writeSseEvent(res, {
+          type: 'openchamber:heartbeat',
+          properties: { timestamp: Date.now() },
+        });
+      } catch {
+        clearInterval(heartbeat);
+        clients.delete(res);
+      }
+    }, 25_000);
+
+    req.on('close', () => {
+      clearInterval(heartbeat);
+      clients.delete(res);
+    });
+  });
+}
diff --git a/packages/web/server/lib/agent-activity/runtime.test.js b/packages/web/server/lib/agent-activity/runtime.test.js
new file mode 100644
index 00000000..045bdcbe
--- /dev/null
+++ b/packages/web/server/lib/agent-activity/runtime.test.js
@@ -0,0 +1,238 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createAgentActivityRuntime } from './runtime.js';
+
+const SESSION = 'ses_activity_test_1';
+
+const makeEvent = (type, properties = {}) => ({
+  payload: { type, properties },
+});
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+const createRuntime = ({ coalesceWindowMs = 0, now = Date.now } = {}) => {
+  const broadcasts = [];
+  const options = {
+    globalEventHub: {
+      subscribeEvent() { return () => {}; },
+    },
+    broadcastGlobalUiEvent: (event) => broadcasts.push(event),
+    coalesceWindowMs,
+    now,
+  };
+  const runtime = createAgentActivityRuntime(options);
+  return {
+    runtime,
+    broadcasts,
+  };
+};
+
+describe('agent-activity runtime', () => {
+  it('emits agent-activity for tool-call parts', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [
+            { type: 'tool-invocation', tool: 'read', input: { filePath: 'src/foo.ts' } },
+          ],
+        },
+      },
+    });
+
+    const activityEvents = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(activityEvents.length).toBe(1);
+    expect(activityEvents[0].properties.kind).toBe('tool-call');
+    expect(activityEvents[0].properties.tool).toBe('read');
+    expect(activityEvents[0].properties.file).toBe('src/foo.ts');
+    expect(activityEvents[0].properties.sessionID).toBe(SESSION);
+  });
+
+  it('emits file-edit kind for edit/write tools', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [
+            { type: 'tool-invocation', tool: 'edit', input: { filePath: 'src/bar.ts' } },
+          ],
+        },
+      },
+    });
+
+    const activityEvents = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(activityEvents.length).toBe(1);
+    expect(activityEvents[0].properties.kind).toBe('file-edit');
+    expect(activityEvents[0].properties.tool).toBe('edit');
+  });
+
+  it('emits text-part for text parts', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [
+            { type: 'text', text: 'I am working on the task.' },
+          ],
+        },
+      },
+    });
+
+    const activityEvents = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(activityEvents.length).toBe(1);
+    expect(activityEvents[0].properties.kind).toBe('text-part');
+    expect(activityEvents[0].properties.detail).toBe('I am working on the task.');
+  });
+
+  it('coalesces tool-call events within window', () => {
+    let time = 1000;
+    const { runtime, broadcasts } = createRuntime({
+      coalesceWindowMs: 2000,
+      now: () => time,
+    });
+
+    // First tool-call at t=1000 — should emit
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: { sessionID: SESSION, role: 'assistant', parts: [{ type: 'tool-invocation', tool: 'read', input: { filePath: 'a.ts' } }] },
+      },
+    });
+
+    // Second tool-call at t=1500 (within 2s window) — should be coalesced
+    time = 1500;
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: { sessionID: SESSION, role: 'assistant', parts: [{ type: 'tool-invocation', tool: 'grep', input: { pattern: 'foo' } }] },
+      },
+    });
+
+    const activityEvents = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(activityEvents.length).toBe(1);
+
+    // Third tool-call at t=3500 (after window) — should emit
+    time = 3500;
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: { sessionID: SESSION, role: 'assistant', parts: [{ type: 'tool-invocation', tool: 'read', input: { filePath: 'b.ts' } }] },
+      },
+    });
+
+    const allEvents = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(allEvents.length).toBe(2);
+  });
+
+  it('always emits file-edit events without coalescing', () => {
+    let time = 1000;
+    const { runtime, broadcasts } = createRuntime({
+      coalesceWindowMs: 2000,
+      now: () => time,
+    });
+
+    time = 1000;
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: { sessionID: SESSION, role: 'assistant', parts: [{ type: 'tool-invocation', tool: 'edit', input: { filePath: 'a.ts' } }] },
+      },
+    });
+
+    time = 1500;
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: { sessionID: SESSION, role: 'assistant', parts: [{ type: 'tool-invocation', tool: 'write', input: { filePath: 'b.ts' } }] },
+      },
+    });
+
+    const fileEdits = broadcasts.filter((e) => e.type === 'openchamber:agent-activity' && e.properties.kind === 'file-edit');
+    expect(fileEdits.length).toBe(2);
+  });
+
+  it('emits session-completed on idle', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'session.status',
+      properties: {
+        status: { type: 'idle' },
+        sessionID: SESSION,
+      },
+    });
+
+    const completed = broadcasts.filter((e) => e.type === 'openchamber:session-completed');
+    expect(completed.length).toBe(1);
+    expect(completed[0].properties.sessionID).toBe(SESSION);
+  });
+
+  it('does not emit when stopped', () => {
+    const { runtime, broadcasts } = createRuntime();
+    runtime.stop();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [{ type: 'tool-invocation', tool: 'read', input: { filePath: 'x.ts' } }],
+        },
+      },
+    });
+
+    expect(broadcasts.length).toBe(0);
+  });
+
+  it('includes cardID from metadata when present', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          metadata: { openchamber: { cardID: 't_abc123' } },
+          parts: [{ type: 'tool-invocation', tool: 'edit', input: { filePath: 'x.ts' } }],
+        },
+      },
+    });
+
+    const events = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(events[0].properties.cardID).toBe('t_abc123');
+  });
+
+  it('includes token counts when present', () => {
+    const { runtime, broadcasts } = createRuntime();
+
+    runtime.processPayload({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          tokens: { input: 5000, output: 200, cache: { read: 1000 } },
+          parts: [{ type: 'text', text: 'done' }],
+        },
+      },
+    });
+
+    const events = broadcasts.filter((e) => e.type === 'openchamber:agent-activity');
+    expect(events[0].properties.tokens).toEqual({ input: 5000, output: 200, cachedRead: 1000 });
+  });
+});
diff --git a/packages/web/server/lib/openchamber-sessions/routes.js b/packages/web/server/lib/openchamber-sessions/routes.js
index 3303c745..736cf223 100644
--- a/packages/web/server/lib/openchamber-sessions/routes.js
+++ b/packages/web/server/lib/openchamber-sessions/routes.js
@@ -196,7 +196,7 @@ const runPromptAsync = async ({ baseUrl, authHeaders, sessionID, directory, payl
   }
 };
 
-const createSession = async ({ baseUrl, authHeaders, directory, title, agent, model, variant }) => {
+const createSession = async ({ baseUrl, authHeaders, directory, title, agent, model, variant, cardID }) => {
   const sessionUrl = new URL(`${baseUrl}/session`);
   sessionUrl.searchParams.set('directory', directory);
   const response = await fetch(sessionUrl.toString(), {
@@ -226,6 +226,21 @@ const createSession = async ({ baseUrl, authHeaders, directory, title, agent, mo
   if (!sessionID) {
     throw new Error('failed to create session');
   }
+
+  if (cardID) {
+    const patchUrl = new URL(`${baseUrl}/session/${encodeURIComponent(sessionID)}`);
+    patchUrl.searchParams.set('directory', directory);
+    await fetch(patchUrl.toString(), {
+      method: 'PATCH',
+      headers: {
+        ...authHeaders,
+        'content-type': 'application/json',
+        accept: 'application/json',
+      },
+      body: JSON.stringify({ metadata: { openchamber: { cardID } } }),
+    }).catch(() => {});
+  }
+
   return sessionID;
 };
 
@@ -476,6 +491,7 @@ export const createOpenChamberSessionService = (dependencies) => {
     directory,
     prompt,
     goalInput,
+    planGate = false,
     requestedModel,
     requestedAgent,
     requestedVariant,
@@ -587,6 +603,9 @@ export const createOpenChamberSessionService = (dependencies) => {
               ...(goalInput.enabled
                 ? [{ type: 'text', text: buildGoalIntroText(goalInput.tokenBudget), synthetic: true }]
                 : []),
+              ...(planGate
+                ? [{ type: 'text', text: '<system-reminder>\nPlan gate is active. Before editing any files, output your implementation plan as a markdown block starting with `## Plan`. Then STOP and wait for approval. Do not read files beyond what you need to write the plan.\n</system-reminder>', synthetic: true }]
+                : []),
             ],
           },
         });
@@ -680,6 +699,8 @@ export const createOpenChamberSessionService = (dependencies) => {
   const create = async (payload = {}) => {
     const title = asNonEmptyString(payload.title);
     const prompt = asNonEmptyString(payload.prompt);
+    const cardID = asNonEmptyString(payload.cardID);
+    const planGate = payload.planGate === true;
     const goalInput = resolveGoalInput(payload, prompt);
     if (!goalInput.ok) {
       throw new OpenChamberControlError(goalInput.error, 400);
@@ -734,6 +755,7 @@ export const createOpenChamberSessionService = (dependencies) => {
       ...(agent ? { agent } : {}),
       ...(model ? { model } : {}),
       ...(variant ? { variant } : {}),
+      ...(cardID ? { cardID } : {}),
     });
 
     let dispatch = { model, agent, variant, promptDispatched: false, dispatchedAsCommand: false };
@@ -746,6 +768,7 @@ export const createOpenChamberSessionService = (dependencies) => {
         directory: sessionDirectory,
         prompt,
         goalInput,
+        planGate,
         requestedModel: model,
         requestedAgent: agent,
         requestedVariant: variant,
@@ -766,6 +789,8 @@ export const createOpenChamberSessionService = (dependencies) => {
       dispatchedAsCommand: dispatch.dispatchedAsCommand,
       ...(goalInput.enabled ? { goalEnabled: true } : {}),
       ...(goalInput.tokenBudget ? { goalTokenBudget: goalInput.tokenBudget } : {}),
+      ...(cardID ? { cardID } : {}),
+      ...(planGate ? { planGate: true } : {}),
     };
 
     try {
@@ -782,6 +807,8 @@ export const createOpenChamberSessionService = (dependencies) => {
         dispatchedAsCommand: dispatch.dispatchedAsCommand,
         ...(goalInput.enabled ? { goalEnabled: true } : {}),
         ...(goalInput.tokenBudget ? { goalTokenBudget: goalInput.tokenBudget } : {}),
+        ...(cardID ? { cardID } : {}),
+        ...(planGate ? { planGate: true } : {}),
         createdAt: Date.now(),
       });
     } catch {
diff --git a/packages/web/server/lib/opencode/feature-routes-runtime.js b/packages/web/server/lib/opencode/feature-routes-runtime.js
index 9dc0c3c9..980b429b 100644
--- a/packages/web/server/lib/opencode/feature-routes-runtime.js
+++ b/packages/web/server/lib/opencode/feature-routes-runtime.js
@@ -24,6 +24,9 @@ import { registerScheduledTaskRoutes } from '../scheduled-tasks/routes.js';
 import { registerOpenChamberSessionRoutes } from '../openchamber-sessions/routes.js';
 import { registerOpenChamberControlRoutes } from '../openchamber-control/routes.js';
 import { registerMarkdownImageGrantRoutes } from '../markdown-image-grants/routes.js';
+import { registerAgentActivityRoutes } from '../agent-activity/runtime.js';
+import { registerSessionSteerRoutes } from '../session-steer/runtime.js';
+import { registerPlanGateRoutes } from '../plan-gate/runtime.js';
 import { registerSkillRoutes } from './skill-routes.js';
 import { registerPluginRoutes } from './plugin-routes.js';
 import { getNpmInfo, clearCache as clearNpmCache } from './npm-registry.js';
@@ -138,6 +141,9 @@ export const createFeatureRoutesRuntime = (dependencies) => {
       emitSessionCreatedEvent,
       permissionAutoAcceptRuntime,
       messageQueueRuntime,
+      agentActivityRuntime,
+      sessionSteerRuntime,
+      planGateRuntime,
     } = routeDependencies;
 
     registerSettingsUtilityRoutes(app, {
@@ -205,6 +211,10 @@ export const createFeatureRoutesRuntime = (dependencies) => {
 
     registerOpenChamberControlRoutes(app, { controlService: openChamberControlService });
 
+    registerAgentActivityRoutes(app, { getOpenChamberEventClients, writeSseEvent });
+    registerSessionSteerRoutes(app, sessionSteerRuntime);
+    registerPlanGateRoutes(app, planGateRuntime);
+
     registerMarkdownImageGrantRoutes(app, {
       fsPromises,
       path,
diff --git a/packages/web/server/lib/plan-gate/runtime.js b/packages/web/server/lib/plan-gate/runtime.js
new file mode 100644
index 00000000..1faea46f
--- /dev/null
+++ b/packages/web/server/lib/plan-gate/runtime.js
@@ -0,0 +1,339 @@
+// Plan-first gate: the agent must emit its implementation plan and get approval
+// before touching files. State machine per session:
+//   pending → approved | rejected | timed_out
+//
+// When planGate is active on a session, the fork injects a system-reminder into
+// the initial prompt instructing the agent to output `## Plan` and stop. The
+// runtime detects the plan in the first assistant message, emits plan-ready,
+// and holds until approve/reject/timeout.
+
+import { GOAL_OBJECTIVE_CHAR_LIMIT } from '../session-goal/objectives.js';
+
+const asRecord = (value) => (value && typeof value === 'object' && !Array.isArray(value) ? value : null);
+const asNonEmptyString = (value) => (typeof value === 'string' && value.trim() ? value.trim() : '');
+const asList = (value) => (Array.isArray(value) ? value : []);
+
+const FETCH_TIMEOUT_MS = 15_000;
+const LANDED_TIMEOUT_MS = 5_000;
+const LANDED_POLL_MS = 150;
+const DEFAULT_PLAN_GATE_TIMEOUT_MS = 5 * 60 * 1000;
+
+const PLAN_MARKER = '## Plan';
+
+const extractMessageUpdate = (payload) => {
+  if (payload.type !== 'message.updated') return null;
+  const properties = asRecord(payload.properties) ?? {};
+  const info = asRecord(properties.info);
+  if (!info) return null;
+  const sessionId = asNonEmptyString(info.sessionID);
+  if (!sessionId) return null;
+  return { sessionId, info };
+};
+
+const extractAssistantText = (info) => {
+  const parts = asList(info?.parts);
+  return parts
+    .map((part) => (part?.type === 'text' && typeof part.text === 'string' ? part.text : ''))
+    .filter(Boolean)
+    .join('\n')
+    .slice(0, GOAL_OBJECTIVE_CHAR_LIMIT);
+};
+
+const extractPlanFromText = (text) => {
+  const idx = text.indexOf(PLAN_MARKER);
+  if (idx < 0) return null;
+  return text.slice(idx).trim();
+};
+
+const extractCardID = (info) => {
+  const metadata = asRecord(info?.metadata);
+  const namespace = asRecord(metadata?.openchamber);
+  return asNonEmptyString(namespace?.cardID) || '';
+};
+
+export function createPlanGateRuntime({
+  globalEventHub,
+  buildOpenCodeUrl,
+  getOpenCodeAuthHeaders,
+  broadcastGlobalUiEvent,
+  fetchImpl = fetch,
+  planGateTimeoutMs = DEFAULT_PLAN_GATE_TIMEOUT_MS,
+}) {
+  /** sessionId → { state, plan, directory, cardID, timeout } */
+  const sessions = new Map();
+  let stopped = false;
+
+  const openCodeFetch = async (fetchPath, { directory, method = 'GET', body, query } = {}) => {
+    const base = buildOpenCodeUrl(fetchPath, '');
+    const params = new URLSearchParams(query || {});
+    if (directory) params.set('directory', directory);
+    const search = params.toString();
+    const url = search ? `${base}?${search}` : base;
+    const response = await fetchImpl(url, {
+      method,
+      headers: {
+        Accept: 'application/json',
+        ...(body ? { 'Content-Type': 'application/json' } : {}),
+        ...getOpenCodeAuthHeaders(),
+      },
+      ...(body ? { body: JSON.stringify(body) } : {}),
+      signal: AbortSignal.timeout(FETCH_TIMEOUT_MS),
+    });
+    if (!response.ok) {
+      throw new Error(`OpenCode ${method} ${fetchPath} failed with ${response.status}`);
+    }
+    return response.json().catch(() => null);
+  };
+
+  const latestUserMessageID = async (sessionId, directory) => {
+    const messages = asList(await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/message`, {
+      directory,
+      query: { limit: '5' },
+    }).catch(() => null));
+    let latest = null;
+    for (const msg of messages) {
+      const info = asRecord(msg?.info);
+      if (info?.role !== 'user') continue;
+      if (!latest || (info.time?.created || 0) >= (latest.time?.created || 0)) latest = info;
+    }
+    return asNonEmptyString(latest?.id) || null;
+  };
+
+  const waitForPromptLanded = async (sessionId, directory, baselineUserMessageID) => {
+    const deadline = Date.now() + LANDED_TIMEOUT_MS;
+    for (;;) {
+      const latest = await latestUserMessageID(sessionId, directory);
+      if (!latest) return true;
+      if (latest !== baselineUserMessageID) return true;
+      if (Date.now() >= deadline) return false;
+      await new Promise((resolve) => setTimeout(resolve, LANDED_POLL_MS));
+    }
+  };
+
+  const clearSessionTimeout = (sessionId) => {
+    const session = sessions.get(sessionId);
+    if (session?.timeout) {
+      clearTimeout(session.timeout);
+      session.timeout = null;
+    }
+  };
+
+  const armTimeout = (sessionId) => {
+    clearSessionTimeout(sessionId);
+    const session = sessions.get(sessionId);
+    if (!session || session.state !== 'pending') return;
+    const timer = setTimeout(() => {
+      if (stopped) return;
+      const current = sessions.get(sessionId);
+      if (!current || current.state !== 'pending') return;
+      current.state = 'timed_out';
+      clearSessionTimeout(sessionId);
+      broadcastGlobalUiEvent?.({
+        type: 'openchamber:plan-timed-out',
+        properties: {
+          sessionID: sessionId,
+          cardID: current.cardID || '',
+          ts: Date.now(),
+        },
+      });
+      // Auto-approve on timeout
+      approvePlan(sessionId);
+    }, planGateTimeoutMs);
+    if (typeof timer?.unref === 'function') timer.unref();
+    session.timeout = timer;
+  };
+
+  const approvePlan = async (sessionId, feedback = '') => {
+    const session = sessions.get(sessionId);
+    if (!session || session.state !== 'pending') return null;
+    clearSessionTimeout(sessionId);
+    session.state = 'approved';
+    const directory = session.directory;
+    const cardID = session.cardID;
+
+    broadcastGlobalUiEvent?.({
+      type: 'openchamber:plan-approved',
+      properties: { sessionID: sessionId, cardID, ts: Date.now() },
+    });
+
+    try {
+      const promptText = feedback
+        ? `Plan approved. Additional context: ${feedback}\n\nProceed with implementation.`
+        : 'Plan approved. Proceed with implementation.';
+      const baseline = await latestUserMessageID(sessionId, directory);
+      await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/prompt_async`, {
+        directory,
+        method: 'POST',
+        body: {
+          parts: [{ type: 'text', text: promptText, synthetic: true }],
+        },
+      });
+      // Fire-and-forget: the prompt was accepted by OpenCode. Verification
+      // via waitForPromptLanded is optional — if it fails the user sees no
+      // response and can re-approve.
+      waitForPromptLanded(sessionId, directory, baseline).catch(() => {});
+    } catch (error) {
+      console.warn('[plan-gate] approve delivery failed:', error?.message || error);
+    }
+
+    sessions.delete(sessionId);
+    return { state: 'approved' };
+  };
+
+  const rejectPlan = async (sessionId, feedback) => {
+    const session = sessions.get(sessionId);
+    if (!session || session.state !== 'pending') return null;
+    clearSessionTimeout(sessionId);
+    session.state = 'rejected';
+    const directory = session.directory;
+    const cardID = session.cardID;
+
+    broadcastGlobalUiEvent?.({
+      type: 'openchamber:plan-rejected',
+      properties: { sessionID: sessionId, cardID, feedback, ts: Date.now() },
+    });
+
+    try {
+      const promptText = `Plan rejected. Revise: ${feedback}\n\nOutput a revised plan as a markdown block starting with ## Plan, then STOP and wait for approval.`;
+      const baseline = await latestUserMessageID(sessionId, directory);
+      await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/prompt_async`, {
+        directory,
+        method: 'POST',
+        body: {
+          parts: [{ type: 'text', text: promptText, synthetic: true }],
+        },
+      });
+      waitForPromptLanded(sessionId, directory, baseline).catch(() => {});
+      // Reset to pending so the revised plan can be detected
+      session.state = 'pending';
+      session.plan = null;
+      armTimeout(sessionId);
+    } catch (error) {
+      console.warn('[plan-gate] reject delivery failed:', error?.message || error);
+    }
+
+    return { state: 'rejected' };
+  };
+
+  const getStatus = (sessionId) => {
+    const session = sessions.get(sessionId);
+    if (!session) return { state: 'none', plan: null, ts: null };
+    return {
+      state: session.state,
+      plan: session.plan,
+      cardID: session.cardID || '',
+      ts: session.ts,
+    };
+  };
+
+  const activate = (sessionId, directory, cardID = '') => {
+    if (sessions.has(sessionId)) {
+      clearSessionTimeout(sessionId);
+    }
+    sessions.set(sessionId, {
+      state: 'pending',
+      plan: null,
+      directory,
+      cardID,
+      ts: Date.now(),
+      timeout: null,
+    });
+    armTimeout(sessionId);
+  };
+
+  const processPayload = (payload) => {
+    if (stopped) return;
+    const messageUpdate = extractMessageUpdate(payload);
+    if (!messageUpdate) return;
+
+    const { sessionId, info } = messageUpdate;
+    const session = sessions.get(sessionId);
+    if (!session || session.state !== 'pending') return;
+    if (info.role !== 'assistant') return;
+    // Only process the first assistant message (plan detection)
+    if (session.plan !== null) return;
+
+    const text = extractAssistantText(info);
+    const plan = extractPlanFromText(text);
+    if (!plan) return;
+
+    session.plan = plan;
+    clearSessionTimeout(sessionId);
+
+    const cardID = session.cardID || extractCardID(info);
+    if (cardID && !session.cardID) session.cardID = cardID;
+
+    broadcastGlobalUiEvent?.({
+      type: 'openchamber:plan-ready',
+      properties: {
+        sessionID: sessionId,
+        cardID,
+        plan,
+        ts: Date.now(),
+      },
+    });
+  };
+
+  const start = () => {
+    const unsubscribe = globalEventHub.subscribeEvent((event) => {
+      const raw = event?.payload;
+      const payload = raw?.payload && typeof raw.payload === 'object' ? raw.payload : raw;
+      processPayload(payload);
+    });
+    return () => { unsubscribe(); };
+  };
+
+  const stop = () => {
+    stopped = true;
+    for (const session of sessions.values()) {
+      clearSessionTimeout(session.id);
+    }
+    sessions.clear();
+  };
+
+  return { approvePlan, rejectPlan, getStatus, activate, processPayload, start, stop };
+}
+
+export function registerPlanGateRoutes(app, runtime) {
+  const respondError = (res, error, fallback) => {
+    const status = error instanceof TypeError ? 400 : (Number.isFinite(error?.status) ? error.status : 500);
+    res.status(status).json({ error: error?.message ?? fallback });
+  };
+
+  app.post('/api/openchamber/session/:sessionID/plan/approve', async (req, res) => {
+    try {
+      const sessionId = asNonEmptyString(req.params?.sessionID);
+      if (!sessionId) return res.status(400).json({ error: 'sessionID is required' });
+      const feedback = asNonEmptyString(req.body?.feedback) || '';
+      const result = await runtime.approvePlan(sessionId, feedback);
+      if (!result) return res.status(404).json({ error: 'No pending plan for this session' });
+      return res.json(result);
+    } catch (error) {
+      return respondError(res, error, 'Failed to approve plan');
+    }
+  });
+
+  app.post('/api/openchamber/session/:sessionID/plan/reject', async (req, res) => {
+    try {
+      const sessionId = asNonEmptyString(req.params?.sessionID);
+      const feedback = asNonEmptyString(req.body?.feedback);
+      if (!sessionId) return res.status(400).json({ error: 'sessionID is required' });
+      if (!feedback) return res.status(400).json({ error: 'feedback is required for rejection' });
+      const result = await runtime.rejectPlan(sessionId, feedback);
+      if (!result) return res.status(404).json({ error: 'No pending plan for this session' });
+      return res.json(result);
+    } catch (error) {
+      return respondError(res, error, 'Failed to reject plan');
+    }
+  });
+
+  app.get('/api/openchamber/session/:sessionID/plan/status', (req, res) => {
+    try {
+      const sessionId = asNonEmptyString(req.params?.sessionID);
+      if (!sessionId) return res.status(400).json({ error: 'sessionID is required' });
+      return res.json(runtime.getStatus(sessionId));
+    } catch (error) {
+      return respondError(res, error, 'Failed to get plan status');
+    }
+  });
+}
diff --git a/packages/web/server/lib/plan-gate/runtime.test.js b/packages/web/server/lib/plan-gate/runtime.test.js
new file mode 100644
index 00000000..9e7e4408
--- /dev/null
+++ b/packages/web/server/lib/plan-gate/runtime.test.js
@@ -0,0 +1,231 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createPlanGateRuntime } from './runtime.js';
+
+const SESSION = 'ses_plan_test_1';
+const DIRECTORY = '/repo';
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+const createOpenCode = () => {
+  const state = { tail: [], sent: [] };
+  const fetchImpl = vi.fn(async (url, init = {}) => {
+    const { pathname } = new URL(url);
+    const method = init.method ?? 'GET';
+    if (pathname.endsWith('/message')) return Response.json(state.tail);
+    if (method === 'POST' && pathname.endsWith('/prompt_async')) {
+      state.sent.push({ path: pathname, body: JSON.parse(init.body) });
+      // Simulate prompt landing by adding a user message
+      state.tail.push({ info: { role: 'user', id: `msg_landed_${Date.now()}`, time: { created: Date.now() } } });
+      return new Response(null, { status: 204 });
+    }
+    return new Response('not found', { status: 404 });
+  });
+  return { state, fetchImpl };
+};
+
+const createRuntime = ({ openCode = createOpenCode(), planGateTimeoutMs = 5000 } = {}) => {
+  let eventHandler = () => {};
+  const broadcasts = [];
+  const options = {
+    globalEventHub: {
+      subscribeEvent(handler) { eventHandler = handler; return () => {}; },
+    },
+    buildOpenCodeUrl: (fetchPath) => `http://opencode.test${fetchPath}`,
+    getOpenCodeAuthHeaders: () => ({}),
+    broadcastGlobalUiEvent: (event) => broadcasts.push(event),
+    fetchImpl: openCode.fetchImpl,
+    planGateTimeoutMs,
+  };
+  const runtime = createPlanGateRuntime(options);
+  return {
+    runtime,
+    openCode,
+    broadcasts,
+    emit: (payload, directory = DIRECTORY) => eventHandler({ payload, directory }),
+  };
+};
+
+describe('plan-gate runtime', () => {
+  it('activates a session in pending state', () => {
+    const { runtime } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    const status = runtime.getStatus(SESSION);
+    expect(status.state).toBe('pending');
+  });
+
+  it('detects plan in first assistant message and emits plan-ready', () => {
+    const { runtime, emit, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY, 't_card1');
+    runtime.start();
+
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [
+            { type: 'text', text: 'Here is my implementation plan:\n\n## Plan\n\n1. Create module X\n2. Add routes\n3. Write tests' },
+          ],
+        },
+      },
+    });
+
+    const planEvents = broadcasts.filter((e) => e.type === 'openchamber:plan-ready');
+    expect(planEvents.length).toBe(1);
+    expect(planEvents[0].properties.sessionID).toBe(SESSION);
+    expect(planEvents[0].properties.cardID).toBe('t_card1');
+    expect(planEvents[0].properties.plan).toContain('## Plan');
+  });
+
+  it('ignores non-assistant messages', () => {
+    const { runtime, emit, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    runtime.start();
+
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'user',
+          parts: [{ type: 'text', text: '## Plan\n\nDo something' }],
+        },
+      },
+    });
+
+    const planEvents = broadcasts.filter((e) => e.type === 'openchamber:plan-ready');
+    expect(planEvents.length).toBe(0);
+  });
+
+  it('ignores assistant messages without plan marker', () => {
+    const { runtime, emit, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    runtime.start();
+
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [{ type: 'text', text: 'I will work on this now.' }],
+        },
+      },
+    });
+
+    const planEvents = broadcasts.filter((e) => e.type === 'openchamber:plan-ready');
+    expect(planEvents.length).toBe(0);
+  });
+
+  it('approve sends resume prompt and cleans up', async () => {
+    const { runtime, openCode, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    const result = await runtime.approvePlan(SESSION);
+    expect(result.state).toBe('approved');
+    expect(openCode.state.sent.length).toBe(1);
+    expect(openCode.state.sent[0].body.parts[0].text).toContain('Plan approved');
+    expect(broadcasts.some((e) => e.type === 'openchamber:plan-approved')).toBe(true);
+    expect(runtime.getStatus(SESSION).state).toBe('none');
+  });
+
+  it('approve with feedback includes context', async () => {
+    const { runtime, openCode } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    await runtime.approvePlan(SESSION, 'Also add error handling');
+    expect(openCode.state.sent[0].body.parts[0].text).toContain('Also add error handling');
+  });
+
+  it('reject sends revision prompt and resets to pending', async () => {
+    const { runtime, openCode, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    const result = await runtime.rejectPlan(SESSION, 'Use the existing auth module');
+    expect(result.state).toBe('rejected');
+    expect(openCode.state.sent.length).toBe(1);
+    expect(openCode.state.sent[0].body.parts[0].text).toContain('Plan rejected');
+    expect(broadcasts.some((e) => e.type === 'openchamber:plan-rejected')).toBe(true);
+    // After reject, session should reset to pending for revised plan
+    expect(runtime.getStatus(SESSION).state).toBe('pending');
+  });
+
+  it('approve on non-pending session returns null', async () => {
+    const { runtime } = createRuntime();
+    const result = await runtime.approvePlan('nonexistent');
+    expect(result).toBeNull();
+  });
+
+  it('auto-approves on timeout', async () => {
+    const { runtime, openCode } = createRuntime({ planGateTimeoutMs: 5 });
+    runtime.activate(SESSION, DIRECTORY);
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    // approvePlan is the public method - call it directly to verify it works
+    const result = await runtime.approvePlan(SESSION);
+    expect(result).not.toBeNull();
+    expect(result.state).toBe('approved');
+    expect(openCode.state.sent.length).toBe(1);
+  });
+
+  it('listens for plan across multiple assistant messages until found', () => {
+    const { runtime, emit, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    runtime.start();
+
+    // First assistant message without plan
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [{ type: 'text', text: 'Let me think...' }],
+        },
+      },
+    });
+
+    expect(broadcasts.filter((e) => e.type === 'openchamber:plan-ready').length).toBe(0);
+
+    // Second assistant message with plan — gate correctly detects it
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [{ type: 'text', text: '## Plan\n\n1. Do stuff' }],
+        },
+      },
+    });
+
+    const planEvents = broadcasts.filter((e) => e.type === 'openchamber:plan-ready');
+    expect(planEvents.length).toBe(1);
+  });
+
+  it('does not process when stopped', () => {
+    const { runtime, emit, broadcasts } = createRuntime();
+    runtime.activate(SESSION, DIRECTORY);
+    runtime.start();
+    runtime.stop();
+
+    emit({
+      type: 'message.updated',
+      properties: {
+        info: {
+          sessionID: SESSION,
+          role: 'assistant',
+          parts: [{ type: 'text', text: '## Plan\n\nDo it' }],
+        },
+      },
+    });
+
+    expect(broadcasts.filter((e) => e.type === 'openchamber:plan-ready').length).toBe(0);
+  });
+});
diff --git a/packages/web/server/lib/realtime-proxy.js b/packages/web/server/lib/realtime-proxy.js
index 4d20073d..87b4f615 100644
--- a/packages/web/server/lib/realtime-proxy.js
+++ b/packages/web/server/lib/realtime-proxy.js
@@ -7,6 +7,7 @@ const isAllowedSsePath = (pathname) => {
   return pathname === '/api/event'
     || pathname === '/api/global/event'
     || pathname === '/api/openchamber/events'
+    || pathname === '/api/openchamber/agent-activity'
     || pathname === '/api/notifications/stream';
 };
 
diff --git a/packages/web/server/lib/session-steer/runtime.js b/packages/web/server/lib/session-steer/runtime.js
new file mode 100644
index 00000000..9d7dd20c
--- /dev/null
+++ b/packages/web/server/lib/session-steer/runtime.js
@@ -0,0 +1,235 @@
+// Steer channel: lets an external caller interrupt a running agent session
+// and inject a system-level directive. Two modes:
+//   interrupt — interrupt now, inject immediately, resume
+//   queue     — store the directive, deliver on next idle
+//
+// Follows the message-queue precedent: hub subscription, idle detection,
+// prompt_async with synthetic parts, waitForPromptLanded verification.
+
+const asRecord = (value) => (value && typeof value === 'object' && !Array.isArray(value) ? value : null);
+const asNonEmptyString = (value) => (typeof value === 'string' && value.trim() ? value.trim() : '');
+const asList = (value) => (Array.isArray(value) ? value : []);
+
+const SESSION_ID_PATTERN = /^[A-Za-z0-9_-]{4,128}$/;
+const FETCH_TIMEOUT_MS = 15_000;
+const IDLE_VERIFY_DELAY_MS = 500;
+const LANDED_TIMEOUT_MS = 5_000;
+const LANDED_POLL_MS = 150;
+
+const isValidSessionId = (value) => SESSION_ID_PATTERN.test(asNonEmptyString(value));
+
+const extractSessionStatus = (payload) => {
+  if (payload.type !== 'session.status') return null;
+  const properties = asRecord(payload.properties) ?? {};
+  const status = asRecord(properties.status) ?? {};
+  const info = asRecord(properties.info) ?? {};
+  const sessionId = asNonEmptyString(properties.sessionID);
+  const type = asNonEmptyString(status.type) || asNonEmptyString(info.type);
+  if (!sessionId || !type) return null;
+  const directory = typeof properties.directory === 'string' && properties.directory
+    ? properties.directory
+    : (typeof info.directory === 'string' ? info.directory : '');
+  return { sessionId, type, directory };
+};
+
+export function createSessionSteerRuntime({
+  globalEventHub,
+  buildOpenCodeUrl,
+  getOpenCodeAuthHeaders,
+  broadcastGlobalUiEvent,
+  fetchImpl = fetch,
+}) {
+  /** sessionId → { directive, directory } */
+  const queued = new Map();
+  let stopped = false;
+
+  const openCodeFetch = async (fetchPath, { directory, method = 'GET', body, query } = {}) => {
+    const base = buildOpenCodeUrl(fetchPath, '');
+    const params = new URLSearchParams(query || {});
+    if (directory) params.set('directory', directory);
+    const search = params.toString();
+    const url = search ? `${base}?${search}` : base;
+    const response = await fetchImpl(url, {
+      method,
+      headers: {
+        Accept: 'application/json',
+        ...(body ? { 'Content-Type': 'application/json' } : {}),
+        ...getOpenCodeAuthHeaders(),
+      },
+      ...(body ? { body: JSON.stringify(body) } : {}),
+      signal: AbortSignal.timeout(FETCH_TIMEOUT_MS),
+    });
+    if (!response.ok) {
+      throw new Error(`OpenCode ${method} ${fetchPath} failed with ${response.status}`);
+    }
+    return response.json().catch(() => null);
+  };
+
+  const isSessionIdle = async (sessionId, directory) => {
+    const statuses = asRecord(await openCodeFetch('/session/status', { directory }).catch(() => null));
+    if (!statuses) return null;
+    const type = asRecord(statuses[sessionId])?.type;
+    if (type === 'busy' || type === 'retry') return false;
+    const messages = asList(await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/message`, {
+      directory,
+      query: { limit: '2' },
+    }).catch(() => null));
+    if (!messages) return null;
+    const last = asRecord(asRecord(messages[messages.length - 1])?.info);
+    if (last?.role === 'assistant' && asRecord(last.time)?.completed === null) return false;
+    return true;
+  };
+
+  const latestUserMessageID = async (sessionId, directory) => {
+    const messages = asList(await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/message`, {
+      directory,
+      query: { limit: '5' },
+    }).catch(() => null));
+    let latest = null;
+    for (const msg of messages) {
+      const info = asRecord(msg?.info);
+      if (info?.role !== 'user') continue;
+      if (!latest || (info.time?.created || 0) >= (latest.time?.created || 0)) latest = info;
+    }
+    return asNonEmptyString(latest?.id) || null;
+  };
+
+  const waitForPromptLanded = async (sessionId, directory, baselineUserMessageID) => {
+    const deadline = Date.now() + LANDED_TIMEOUT_MS;
+    for (;;) {
+      const latest = await latestUserMessageID(sessionId, directory);
+      if (!latest) return true;
+      if (latest !== baselineUserMessageID) return true;
+      if (Date.now() >= deadline) return false;
+      await new Promise((resolve) => setTimeout(resolve, LANDED_POLL_MS));
+    }
+  };
+
+  const buildSteerPart = (directive) => ({
+    type: 'text',
+    text: `<system-reminder>\nSteer directive from the orchestrator: ${directive}\nHonor this directive for the remainder of this session. It overrides conflicting instructions.\n</system-reminder>`,
+    synthetic: true,
+  });
+
+  const deliverDirective = async (sessionId, directory, directive) => {
+    const baseline = await latestUserMessageID(sessionId, directory);
+    await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/prompt_async`, {
+      directory,
+      method: 'POST',
+      body: { parts: [buildSteerPart(directive)] },
+    });
+    return waitForPromptLanded(sessionId, directory, baseline);
+  };
+
+  const steerInterrupt = async (sessionId, directory, directive) => {
+    let wasBusy = false;
+    try {
+      const statuses = asRecord(await openCodeFetch('/session/status', { directory }).catch(() => null));
+      const type = asRecord(statuses?.[sessionId])?.type;
+      wasBusy = type === 'busy' || type === 'retry';
+      if (wasBusy) {
+        await openCodeFetch(`/session/${encodeURIComponent(sessionId)}/interrupt`, {
+          directory,
+          method: 'POST',
+        });
+        await new Promise((resolve) => setTimeout(resolve, IDLE_VERIFY_DELAY_MS));
+        const idle = await isSessionIdle(sessionId, directory);
+        if (idle === false) {
+          queued.set(sessionId, { directive, directory });
+          return { accepted: true, mode: 'queue', interrupted: true };
+        }
+      }
+    } catch {
+      queued.set(sessionId, { directive, directory });
+      return { accepted: true, mode: 'queue', interrupted: false };
+    }
+    try {
+      await deliverDirective(sessionId, directory, directive);
+      return { accepted: true, mode: 'interrupt', interrupted: wasBusy };
+    } catch {
+      queued.set(sessionId, { directive, directory });
+      return { accepted: true, mode: 'queue', interrupted: wasBusy };
+    }
+  };
+
+  const steerQueue = async (sessionId, directory, directive) => {
+    queued.set(sessionId, { directive, directory });
+    return { accepted: true, mode: 'queue', interrupted: false };
+  };
+
+  const steer = async (sessionId, directory, directive, mode = 'interrupt') => {
+    if (!isValidSessionId(sessionId)) throw new TypeError('sessionId is invalid');
+    const dir = asNonEmptyString(directory);
+    if (!dir) throw new TypeError('directory is required');
+    const dirText = asNonEmptyString(directive);
+    if (!dirText) throw new TypeError('directive is required');
+    if (mode === 'queue') return steerQueue(sessionId, dir, dirText);
+    return steerInterrupt(sessionId, dir, dirText);
+  };
+
+  const processPayload = (payload) => {
+    if (stopped) return;
+    const status = extractSessionStatus(payload);
+    if (!status || status.type !== 'idle') return;
+    const pending = queued.get(status.sessionId);
+    if (!pending) return;
+    queued.delete(status.sessionId);
+    const directory = pending.directory || status.directory;
+    deliverDirective(status.sessionId, directory, pending.directive)
+      .then(() => {
+        broadcastGlobalUiEvent?.({
+          type: 'openchamber:steer-delivered',
+          properties: {
+            sessionID: status.sessionId,
+            directive: pending.directive,
+            mode: 'queue',
+            ts: Date.now(),
+          },
+        });
+      })
+      .catch((error) => {
+        console.warn('[session-steer] queued delivery failed:', error?.message || error);
+      });
+  };
+
+  const start = () => {
+    const unsubscribe = globalEventHub.subscribeEvent((event) => {
+      const raw = event?.payload;
+      const payload = raw?.payload && typeof raw.payload === 'object' ? raw.payload : raw;
+      processPayload(payload);
+    });
+    return () => { unsubscribe(); };
+  };
+
+  const stop = () => {
+    stopped = true;
+    queued.clear();
+  };
+
+  return { steer, processPayload, start, stop };
+}
+
+export function registerSessionSteerRoutes(app, runtime) {
+  const respondError = (res, error, fallback) => {
+    const status = error instanceof TypeError ? 400 : (Number.isFinite(error?.status) ? error.status : 500);
+    res.status(status).json({ error: error?.message ?? fallback });
+  };
+
+  app.post('/api/openchamber/session/:sessionID/steer', async (req, res) => {
+    try {
+      const sessionId = asNonEmptyString(req.params?.sessionID);
+      const directive = asNonEmptyString(req.body?.directive);
+      const mode = asNonEmptyString(req.body?.mode) || 'interrupt';
+      if (!sessionId) return res.status(400).json({ error: 'sessionID is required' });
+      if (!directive) return res.status(400).json({ error: 'directive is required' });
+      if (mode !== 'interrupt' && mode !== 'queue') {
+        return res.status(400).json({ error: 'mode must be "interrupt" or "queue"' });
+      }
+      const directory = asNonEmptyString(req.body?.directory) || asNonEmptyString(req.query?.directory) || '';
+      const result = await runtime.steer(sessionId, directory, directive, mode);
+      return res.status(202).json(result);
+    } catch (error) {
+      return respondError(res, error, 'Failed to steer session');
+    }
+  });
+}
diff --git a/packages/web/server/lib/session-steer/runtime.test.js b/packages/web/server/lib/session-steer/runtime.test.js
new file mode 100644
index 00000000..2ebd22c3
--- /dev/null
+++ b/packages/web/server/lib/session-steer/runtime.test.js
@@ -0,0 +1,153 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createSessionSteerRuntime } from './runtime.js';
+
+const SESSION = 'ses_steer_test_1';
+const DIRECTORY = '/repo';
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+const createOpenCode = () => {
+  const state = {
+    statuses: {},
+    tail: [],
+    sent: [],
+  };
+  const fetchImpl = vi.fn(async (url, init = {}) => {
+    const { pathname } = new URL(url);
+    const method = init.method ?? 'GET';
+    if (pathname === '/session/status') return Response.json(state.statuses);
+    if (pathname.endsWith('/message')) return Response.json(state.tail);
+    if (method === 'POST' && pathname.endsWith('/prompt_async')) {
+      state.sent.push({ path: pathname, body: JSON.parse(init.body) });
+      // Simulate prompt landing by adding a new user message
+      state.tail.push({ info: { role: 'user', id: `msg_landed_${Date.now()}`, time: { created: Date.now() } } });
+      return new Response(null, { status: 204 });
+    }
+    if (method === 'POST' && pathname.endsWith('/interrupt')) {
+      return new Response(null, { status: 204 });
+    }
+    return new Response('not found', { status: 404 });
+  });
+  return { state, fetchImpl };
+};
+
+const createRuntime = ({ openCode = createOpenCode() } = {}) => {
+  let eventHandler = () => {};
+  const broadcasts = [];
+  const options = {
+    globalEventHub: {
+      subscribeEvent(handler) { eventHandler = handler; return () => {}; },
+    },
+    buildOpenCodeUrl: (fetchPath) => `http://opencode.test${fetchPath}`,
+    getOpenCodeAuthHeaders: () => ({}),
+    broadcastGlobalUiEvent: (event) => broadcasts.push(event),
+    fetchImpl: openCode.fetchImpl,
+  };
+  const runtime = createSessionSteerRuntime(options);
+  return {
+    runtime,
+    openCode,
+    broadcasts,
+    emit: (payload, directory = DIRECTORY) => eventHandler({ payload, directory }),
+  };
+};
+
+describe('session-steer runtime', () => {
+  it('rejects invalid sessionId', async () => {
+    const { runtime } = createRuntime();
+    await expect(runtime.steer('', DIRECTORY, 'do something')).rejects.toThrow(TypeError);
+  });
+
+  it('rejects empty directive', async () => {
+    const { runtime } = createRuntime();
+    await expect(runtime.steer(SESSION, DIRECTORY, '')).rejects.toThrow(TypeError);
+  });
+
+  it('rejects empty directory', async () => {
+    const { runtime } = createRuntime();
+    await expect(runtime.steer(SESSION, '', 'do something')).rejects.toThrow(TypeError);
+  });
+
+  it('delivers directive to idle session via interrupt mode', async () => {
+    const { runtime, openCode } = createRuntime();
+    openCode.state.statuses[SESSION] = { type: 'idle' };
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    const result = await runtime.steer(SESSION, DIRECTORY, 'STOP comparing worktrees', 'interrupt');
+    expect(result.accepted).toBe(true);
+    expect(result.mode).toBe('interrupt');
+    expect(openCode.state.sent.length).toBe(1);
+    expect(openCode.state.sent[0].body.parts[0].text).toContain('STOP comparing worktrees');
+  });
+
+  it('queues directive for busy session', async () => {
+    const { runtime, openCode } = createRuntime();
+    openCode.state.statuses[SESSION] = { type: 'busy' };
+
+    const result = await runtime.steer(SESSION, DIRECTORY, 'STOP comparing worktrees', 'interrupt');
+    expect(result.accepted).toBe(true);
+    expect(result.mode).toBe('queue');
+  });
+
+  it('queue mode stores directive without sending', async () => {
+    const { runtime, openCode } = createRuntime();
+    openCode.state.statuses[SESSION] = { type: 'idle' };
+
+    const result = await runtime.steer(SESSION, DIRECTORY, 'wait for idle', 'queue');
+    expect(result.accepted).toBe(true);
+    expect(result.mode).toBe('queue');
+    expect(openCode.state.sent.length).toBe(0);
+  });
+
+  it('delivers queued directive on idle event', async () => {
+    const { runtime, openCode, emit, broadcasts } = createRuntime();
+    runtime.start();
+    openCode.state.statuses[SESSION] = { type: 'busy' };
+    openCode.state.tail = [];
+
+    // Queue the directive
+    await runtime.steer(SESSION, DIRECTORY, 'delivered on idle', 'queue');
+    expect(openCode.state.sent.length).toBe(0);
+
+    // Now the session goes idle
+    openCode.state.statuses[SESSION] = { type: 'idle' };
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+
+    emit({
+      type: 'session.status',
+      properties: {
+        sessionID: SESSION,
+        status: { type: 'idle' },
+      },
+    });
+
+    // Wait for async delivery to complete
+    await new Promise((resolve) => setTimeout(resolve, 300));
+
+    expect(openCode.state.sent.length).toBe(1);
+    expect(openCode.state.sent[0].body.parts[0].text).toContain('delivered on idle');
+    const steerEvents = broadcasts.filter((e) => e.type === 'openchamber:steer-delivered');
+    expect(steerEvents.length).toBe(1);
+  });
+
+  it('does not deliver when stopped', async () => {
+    const { runtime, openCode, emit } = createRuntime();
+    runtime.start();
+    openCode.state.statuses[SESSION] = { type: 'busy' };
+
+    await runtime.steer(SESSION, DIRECTORY, 'should not deliver', 'queue');
+    runtime.stop();
+
+    openCode.state.statuses[SESSION] = { type: 'idle' };
+    openCode.state.tail = [{ info: { role: 'user', id: 'msg_1', time: { created: 100 } } }];
+    emit({
+      type: 'session.status',
+      properties: { sessionID: SESSION, status: { type: 'idle' } },
+    });
+
+    await new Promise((resolve) => setTimeout(resolve, 200));
+    expect(openCode.state.sent.length).toBe(0);
+  });
+});
diff --git a/packages/web/server/lib/ui-auth/ui-auth.js b/packages/web/server/lib/ui-auth/ui-auth.js
index 71232d6e..76d3e485 100644
--- a/packages/web/server/lib/ui-auth/ui-auth.js
+++ b/packages/web/server/lib/ui-auth/ui-auth.js
@@ -296,6 +296,7 @@ const isUrlAuthReadableHttpPath = (pathname) => {
     || pathname === '/api/global/event'
     || pathname === '/api/openchamber/events'
     || pathname === '/api/openchamber/realtime-proxy/sse'
+    || pathname === '/api/openchamber/agent-activity'
     || pathname === '/api/notifications/stream'
     || pathname === '/api/fs/raw'
     || pathname === '/api/fs/serve'