diff --git a/packages/vscode/src/ChatViewProvider.ts b/packages/vscode/src/ChatViewProvider.ts
index 7c01a5f4..545be6e8 100644
--- a/packages/vscode/src/ChatViewProvider.ts
+++ b/packages/vscode/src/ChatViewProvider.ts
@@ -142,7 +142,13 @@ export class ChatViewProvider implements vscode.WebviewViewProvider {
       });
     }
   }
-  
+
+  public postMessage(message: unknown): void {
+    if (this._view) {
+      this._view.webview.postMessage(message);
+    }
+  }
+
   private _sendCachedState() {
     if (!this._view) {
       return;
diff --git a/packages/vscode/src/extension.ts b/packages/vscode/src/extension.ts
index db022360..d1a7974f 100644
--- a/packages/vscode/src/extension.ts
+++ b/packages/vscode/src/extension.ts
@@ -3,6 +3,7 @@ import { ChatViewProvider } from './ChatViewProvider';
 import { AgentManagerPanelProvider } from './AgentManagerPanelProvider';
 import { SessionEditorPanelProvider } from './SessionEditorPanelProvider';
 import { createOpenCodeManager, type OpenCodeManager } from './opencode';
+import { startGlobalEventWatcher, stopGlobalEventWatcher, setChatViewProvider } from './sessionActivityWatcher';
 
 let chatViewProvider: ChatViewProvider | undefined;
 let agentManagerProvider: AgentManagerPanelProvider | undefined;
@@ -539,6 +540,15 @@ export async function activate(context: vscode.ExtensionContext) {
       chatViewProvider?.updateConnectionStatus(status, error);
       agentManagerProvider?.updateConnectionStatus(status, error);
       sessionEditorProvider?.updateConnectionStatus(status, error);
+
+      // Start/stop global event watcher based on connection status
+      // Mirrors web server and desktop Tauri behavior
+      if (status === 'connected' && chatViewProvider && openCodeManager) {
+        setChatViewProvider(chatViewProvider);
+        void startGlobalEventWatcher(openCodeManager, chatViewProvider);
+      } else if (status === 'disconnected' || status === 'error') {
+        stopGlobalEventWatcher();
+      }
     })
   );
 
@@ -548,6 +558,7 @@ export async function activate(context: vscode.ExtensionContext) {
 }
 
 export async function deactivate() {
+  stopGlobalEventWatcher();
   await openCodeManager?.stop();
   openCodeManager = undefined;
   chatViewProvider = undefined;
diff --git a/packages/vscode/src/sessionActivityWatcher.ts b/packages/vscode/src/sessionActivityWatcher.ts
new file mode 100644
index 00000000..8f82b68e
--- /dev/null
+++ b/packages/vscode/src/sessionActivityWatcher.ts
@@ -0,0 +1,280 @@
+import type { OpenCodeManager } from './opencode';
+
+// Session activity tracking (mirrors web server and desktop Tauri behavior)
+type ActivityPhase = 'idle' | 'busy' | 'cooldown';
+
+interface SessionActivity {
+  sessionId: string;
+  phase: ActivityPhase;
+}
+
+const sessionActivityPhases = new Map<string, { phase: ActivityPhase; updatedAt: number }>();
+const sessionActivityCooldowns = new Map<string, NodeJS.Timeout>();
+const SESSION_COOLDOWN_DURATION_MS = 2000;
+
+let globalEventWatcherAbortController: AbortController | null = null;
+let chatViewProvider: { postMessage: (message: unknown) => void } | null = null;
+
+const setSessionActivityPhase = (sessionId: string, phase: ActivityPhase): void => {
+  if (!sessionId) return;
+
+  // Cancel existing cooldown timer
+  const existingTimer = sessionActivityCooldowns.get(sessionId);
+  if (existingTimer) {
+    clearTimeout(existingTimer);
+    sessionActivityCooldowns.delete(sessionId);
+  }
+
+  const current = sessionActivityPhases.get(sessionId);
+  if (current?.phase === phase) return; // No change
+
+  sessionActivityPhases.set(sessionId, { phase, updatedAt: Date.now() });
+
+  // Notify webview if available
+  if (chatViewProvider) {
+    chatViewProvider.postMessage({
+      type: 'openchamber:session-activity',
+      properties: {
+        sessionId,
+        phase,
+      },
+    });
+  }
+
+  // Schedule transition from cooldown to idle
+  if (phase === 'cooldown') {
+    const timer = setTimeout(() => {
+      const now = sessionActivityPhases.get(sessionId);
+      if (now?.phase === 'cooldown') {
+        sessionActivityPhases.set(sessionId, { phase: 'idle', updatedAt: Date.now() });
+        if (chatViewProvider) {
+          chatViewProvider.postMessage({
+            type: 'openchamber:session-activity',
+            properties: {
+              sessionId,
+              phase: 'idle',
+            },
+          });
+        }
+      }
+      sessionActivityCooldowns.delete(sessionId);
+    }, SESSION_COOLDOWN_DURATION_MS);
+    sessionActivityCooldowns.set(sessionId, timer);
+  }
+};
+
+const deriveSessionActivity = (payload: Record<string, unknown>): SessionActivity | null => {
+  if (!payload || typeof payload !== 'object') {
+    return null;
+  }
+
+  const type = payload.type as string;
+  const properties = (payload.properties ?? payload) as Record<string, unknown>;
+
+  if (type === 'session.status') {
+    const status = properties?.status as Record<string, unknown> | undefined;
+    const sessionId = (properties?.sessionID ?? properties?.sessionId) as string;
+    const statusType = status?.type as string;
+
+    if (typeof sessionId === 'string' && sessionId.length > 0 && typeof statusType === 'string') {
+      const phase = statusType === 'busy' || statusType === 'retry' ? 'busy' : 'idle';
+      return { sessionId, phase };
+    }
+  }
+
+  if (type === 'message.updated' || type === 'message.part.updated') {
+    const info = properties?.info as Record<string, unknown> | undefined;
+    const sessionId = (info?.sessionID ?? info?.sessionId ?? properties?.sessionID ?? properties?.sessionId) as string;
+    const role = info?.role as string;
+    const finish = info?.finish as string;
+    if (typeof sessionId === 'string' && sessionId.length > 0 && role === 'assistant' && finish === 'stop') {
+      return { sessionId, phase: 'cooldown' };
+    }
+  }
+
+  if (type === 'session.idle') {
+    const sessionId = (properties?.sessionID ?? properties?.sessionId) as string;
+    if (typeof sessionId === 'string' && sessionId.length > 0) {
+      return { sessionId, phase: 'idle' };
+    }
+  }
+
+  return null;
+};
+
+const parseSseDataPayload = (block: string): Record<string, unknown> | null => {
+  if (!block) {
+    return null;
+  }
+
+  const lines = block.split('\n');
+  const dataLines: string[] = [];
+
+  for (const line of lines) {
+    if (line.startsWith('data:')) {
+      dataLines.push(line.slice(5).replace(/^\s/, ''));
+    }
+  }
+
+  if (dataLines.length === 0) {
+    return null;
+  }
+
+  const payloadText = dataLines.join('\n').trim();
+  if (!payloadText) {
+    return null;
+  }
+
+  try {
+    return JSON.parse(payloadText) as Record<string, unknown>;
+  } catch {
+    return null;
+  }
+};
+
+const waitForOpenCodePort = async (manager: OpenCodeManager, timeoutMs = 30000): Promise<number | null> => {
+  const start = Date.now();
+  while (Date.now() - start < timeoutMs) {
+    const apiUrl = manager.getApiUrl();
+    if (apiUrl) {
+      try {
+        const url = new URL(apiUrl);
+        if (url.port) {
+          return parseInt(url.port, 10);
+        }
+      } catch {
+        // ignore
+      }
+    }
+    await new Promise(r => setTimeout(r, 500));
+  }
+  return null;
+};
+
+const buildOpenCodeUrl = (pathname: string, baseUrl: string): string => {
+  const normalized = baseUrl.replace(/\/+$/, '');
+  return `${normalized}${pathname}`;
+};
+
+export const startGlobalEventWatcher = async (
+  manager: OpenCodeManager,
+  provider: { postMessage: (message: unknown) => void }
+): Promise<void> => {
+  if (globalEventWatcherAbortController) {
+    return;
+  }
+
+  chatViewProvider = provider;
+
+  const port = await waitForOpenCodePort(manager);
+  if (!port) {
+    console.warn('[VSCode:Activity] OpenCode port unavailable; will retry');
+    setTimeout(() => startGlobalEventWatcher(manager, provider), 2000);
+    return;
+  }
+
+  globalEventWatcherAbortController = new AbortController();
+  const signal = globalEventWatcherAbortController.signal;
+
+  let attempt = 0;
+
+  const run = async (): Promise<void> => {
+    while (!signal.aborted) {
+      attempt += 1;
+      let upstream: Response | null = null;
+      let reader: ReadableStreamDefaultReader<Uint8Array> | null = null;
+
+      try {
+        const baseUrl = manager.getApiUrl();
+        if (!baseUrl) {
+          throw new Error('OpenCode API URL not available');
+        }
+
+        const url = buildOpenCodeUrl('/global/event', baseUrl);
+        upstream = await fetch(url, {
+          headers: {
+            Accept: 'text/event-stream',
+            'Cache-Control': 'no-cache',
+            Connection: 'keep-alive',
+          },
+          signal,
+        });
+
+        if (!upstream.ok || !upstream.body) {
+          throw new Error(`bad status ${upstream.status}`);
+        }
+
+        console.log('[VSCode:Activity] connected');
+
+        const decoder = new TextDecoder();
+        reader = upstream.body.getReader();
+        let buffer = '';
+
+        while (!signal.aborted) {
+          const { value, done } = await reader.read();
+          if (done) {
+            break;
+          }
+
+          buffer += decoder.decode(value, { stream: true }).replace(/\r\n/g, '\n');
+
+          let separatorIndex: number;
+          while ((separatorIndex = buffer.indexOf('\n\n')) !== -1) {
+            const block = buffer.slice(0, separatorIndex);
+            buffer = buffer.slice(separatorIndex + 2);
+            const payload = parseSseDataPayload(block);
+            if (payload) {
+              const activity = deriveSessionActivity(payload);
+              if (activity) {
+                setSessionActivityPhase(activity.sessionId, activity.phase);
+              }
+            }
+          }
+        }
+      } catch (error) {
+        if (signal.aborted) {
+          return;
+        }
+        console.warn('[VSCode:Activity] disconnected', error instanceof Error ? error.message : error);
+      } finally {
+        try {
+          if (reader) {
+            await reader.cancel();
+          } else if (upstream?.body && !(upstream.body as ReadableStream<Uint8Array>).locked) {
+            await upstream.body.cancel();
+          }
+        } catch {
+          // ignore
+        }
+      }
+
+      const backoffMs = Math.min(1000 * Math.pow(2, Math.min(attempt, 5)), 30000);
+      await new Promise(r => setTimeout(r, backoffMs));
+    }
+  };
+
+  void run();
+};
+
+export const stopGlobalEventWatcher = (): void => {
+  if (!globalEventWatcherAbortController) {
+    return;
+  }
+  try {
+    globalEventWatcherAbortController.abort();
+  } catch {
+    // ignore
+  }
+  globalEventWatcherAbortController = null;
+  chatViewProvider = null;
+
+  // Clear all cooldown timers
+  for (const timer of sessionActivityCooldowns.values()) {
+    clearTimeout(timer);
+  }
+  sessionActivityCooldowns.clear();
+};
+
+export const setChatViewProvider = (provider: { postMessage: (message: unknown) => void } | null): void => {
+  chatViewProvider = provider;
+};