fix: sidebar agent uses extension's activeTabUrl instead of stale Playwright URL

When the user navigates manually in headed Chrome, Playwright's page.url()
stays on the old page. The sidebar agent was using this stale URL in its
system prompt, causing it to navigate to the wrong page (e.g., Hacker News
instead of the user's current page).

The Chrome extension now captures the active tab URL via chrome.tabs.query()
and sends it as activeTabUrl in the /sidebar-command POST body. The server
prefers this over Playwright's URL. The URL is sanitized (http/https only,
control chars stripped, 2048 char limit) to prevent prompt injection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

browse/src/server.ts

@@ -18,6 +18,7 @@ import { handleReadCommand } from './read-commands';
 import { handleWriteCommand } from './write-commands';
 import { handleMetaCommand } from './meta-commands';
 import { handleCookiePickerRoute } from './cookie-picker-routes';
+import { sanitizeExtensionUrl } from './sidebar-utils';
 import { COMMAND_DESCRIPTIONS } from './commands';
 import { handleSnapshot, SNAPSHOT_FLAGS } from './snapshot';
 import { resolveConfig, ensureStateDir, readVersionHash } from './config';
@@ -123,7 +124,7 @@ let sidebarSession: SidebarSession | null = null;
 let agentProcess: ChildProcess | null = null;
 let agentStatus: 'idle' | 'processing' | 'hung' = 'idle';
 let agentStartTime: number | null = null;
-let messageQueue: Array<{message: string, ts: string}> = [];
+let messageQueue: Array<{message: string, ts: string, extensionUrl?: string | null}> = [];
 let currentMessage: string | null = null;
 let chatBuffer: ChatEntry[] = [];
 let chatNextId = 0;
@@ -371,18 +372,27 @@ function processAgentEvent(event: any): void {
   }
 }
 
-function spawnClaude(userMessage: string): void {
+function spawnClaude(userMessage: string, extensionUrl?: string | null): void {
   agentStatus = 'processing';
   agentStartTime = Date.now();
   currentMessage = userMessage;
 
-  const pageUrl = browserManager.getCurrentUrl() || 'about:blank';
+  // Prefer the URL from the Chrome extension (what the user actually sees)
+  // over Playwright's page.url() which can be stale in headed mode.
+  const sanitizedExtUrl = sanitizeExtensionUrl(extensionUrl);
+  const playwrightUrl = browserManager.getCurrentUrl() || 'about:blank';
+  const pageUrl = sanitizedExtUrl || playwrightUrl;
   const B = BROWSE_BIN;
   const systemPrompt = [
     'You are a browser assistant running in a Chrome sidebar.',
-    `Current page: ${pageUrl}`,
+    `The user is currently viewing: ${pageUrl}`,
     `Browse binary: ${B}`,
     '',
+    'IMPORTANT: You are controlling a SHARED browser. The user may have navigated',
+    'manually. Always run `' + B + ' url` first to check the actual current URL.',
+    'If it differs from above, the user navigated — work with the ACTUAL page.',
+    'Do NOT navigate away from the user\'s current page unless they ask you to.',
+    '',
     'Commands (run via bash):',
     `  ${B} goto <url>    ${B} click <@ref>    ${B} fill <@ref> <text>`,
     `  ${B} snapshot -i   ${B} text            ${B} screenshot`,
@@ -404,8 +414,8 @@ function spawnClaude(userMessage: string): void {
   // fails with ENOENT on everything, including /bin/bash). Instead,
   // write the command to a queue file that the sidebar-agent process
   // (running as non-compiled bun) picks up and spawns claude.
-  const gstackDir = path.join(process.env.HOME || '/tmp', '.gstack');
-  const agentQueue = path.join(gstackDir, 'sidebar-agent-queue.jsonl');
+  const agentQueue = process.env.SIDEBAR_QUEUE_PATH || path.join(process.env.HOME || '/tmp', '.gstack', 'sidebar-agent-queue.jsonl');
+  const gstackDir = path.dirname(agentQueue);
   const entry = JSON.stringify({
     ts: new Date().toISOString(),
     message: userMessage,
@@ -414,6 +424,7 @@ function spawnClaude(userMessage: string): void {
     stateFile: config.stateFile,
     cwd: (sidebarSession as any)?.worktreePath || process.cwd(),
     sessionId: sidebarSession?.claudeSessionId || null,
+    pageUrl: pageUrl,
   });
   try {
     fs.mkdirSync(gstackDir, { recursive: true });
@@ -781,12 +792,16 @@ async function start() {
   const port = await findPort();
 
   // Launch browser (headless or headed with extension)
-  const headed = process.env.BROWSE_HEADED === '1';
-  if (headed) {
-    await browserManager.launchHeaded();
-    console.log(`[browse] Launched headed Chromium with extension`);
-  } else {
-    await browserManager.launch();
+  // BROWSE_HEADLESS_SKIP=1 skips browser launch entirely (for HTTP-only testing)
+  const skipBrowser = process.env.BROWSE_HEADLESS_SKIP === '1';
+  if (!skipBrowser) {
+    const headed = process.env.BROWSE_HEADED === '1';
+    if (headed) {
+      await browserManager.launchHeaded();
+      console.log(`[browse] Launched headed Chromium with extension`);
+    } else {
+      await browserManager.launch();
+    }
   }
 
   const startTime = Date.now();
@@ -935,17 +950,21 @@ async function start() {
         if (!msg) {
           return new Response(JSON.stringify({ error: 'Empty message' }), { status: 400, headers: { 'Content-Type': 'application/json' } });
         }
+        // The Chrome extension sends the active tab's URL — prefer it over
+        // Playwright's page.url() which can be stale in headed mode when
+        // the user navigates manually.
+        const extensionUrl = body.activeTabUrl || null;
         const ts = new Date().toISOString();
         addChatEntry({ ts, role: 'user', message: msg });
         if (sidebarSession) { sidebarSession.lastActiveAt = ts; saveSession(); }
 
         if (agentStatus === 'idle') {
-          spawnClaude(msg);
+          spawnClaude(msg, extensionUrl);
           return new Response(JSON.stringify({ ok: true, processing: true }), {
             status: 200, headers: { 'Content-Type': 'application/json' },
           });
         } else if (messageQueue.length < MAX_QUEUE) {
-          messageQueue.push({ message: msg, ts });
+          messageQueue.push({ message: msg, ts, extensionUrl });
           return new Response(JSON.stringify({ ok: true, queued: true, position: messageQueue.length }), {
             status: 200, headers: { 'Content-Type': 'application/json' },
           });
@@ -979,7 +998,7 @@ async function start() {
         // Process next in queue
         if (messageQueue.length > 0) {
           const next = messageQueue.shift()!;
-          spawnClaude(next.message);
+          spawnClaude(next.message, next.extensionUrl);
         }
         return new Response(JSON.stringify({ ok: true }), { status: 200, headers: { 'Content-Type': 'application/json' } });
       }
@@ -1065,7 +1084,7 @@ async function start() {
           // Process next queued message
           if (messageQueue.length > 0) {
             const next = messageQueue.shift()!;
-            spawnClaude(next.message);
+            spawnClaude(next.message, next.extensionUrl);
           } else {
             agentStatus = 'idle';
           }

extension/background.js

@@ -194,17 +194,23 @@ chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
       sendResponse({ error: 'Not connected' });
       return true;
     }
-    fetch(`${base}/sidebar-command`, {
-      method: 'POST',
-      headers: {
-        'Content-Type': 'application/json',
-        'Authorization': `Bearer ${authToken}`,
-      },
-      body: JSON.stringify({ message: msg.message }),
-    })
-      .then(r => r.json())
-      .then(data => sendResponse(data))
-      .catch(err => sendResponse({ error: err.message }));
+    // Capture the active tab's URL so the sidebar agent knows what page
+    // the user is actually looking at (Playwright's page.url() can be stale
+    // if the user navigated manually in headed mode).
+    chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {
+      const activeTabUrl = tabs?.[0]?.url || null;
+      fetch(`${base}/sidebar-command`, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': `Bearer ${authToken}`,
+        },
+        body: JSON.stringify({ message: msg.message, activeTabUrl }),
+      })
+        .then(r => r.json())
+        .then(data => sendResponse(data))
+        .catch(err => sendResponse({ error: err.message }));
+    });
     return true;
   }
 });