diff --git a/browse/test/sidebar-agent.test.ts b/browse/test/sidebar-agent.test.ts
index 2c8d49e9..ee77a33b 100644
--- a/browse/test/sidebar-agent.test.ts
+++ b/browse/test/sidebar-agent.test.ts
@@ -67,6 +67,74 @@ function writeToInbox(
   return finalFile;
 }
 
+/** Shorten paths — same logic as sidebar-agent.ts shorten() */
+function shorten(str: string): string {
+  return str
+    .replace(/\/Users\/[^/]+/g, '~')
+    .replace(/\/conductor\/workspaces\/[^/]+\/[^/]+/g, '')
+    .replace(/\.claude\/skills\/gstack\//g, '')
+    .replace(/browse\/dist\/browse/g, '$B');
+}
+
+/** describeToolCall — replicated from sidebar-agent.ts for unit testing */
+function describeToolCall(tool: string, input: any): string {
+  if (!input) return '';
+
+  if (tool === 'Bash' && input.command) {
+    const cmd = input.command;
+    const browseMatch = cmd.match(/\$B\s+(\w+)|browse[^\s]*\s+(\w+)/);
+    if (browseMatch) {
+      const browseCmd = browseMatch[1] || browseMatch[2];
+      const args = cmd.split(/\s+/).slice(2).join(' ');
+      switch (browseCmd) {
+        case 'goto': return `Opening ${args.replace(/['"]/g, '')}`;
+        case 'snapshot': return args.includes('-i') ? 'Scanning for interactive elements' : args.includes('-D') ? 'Checking what changed' : 'Taking a snapshot of the page';
+        case 'screenshot': return `Saving screenshot${args ? ` to ${shorten(args)}` : ''}`;
+        case 'click': return `Clicking ${args}`;
+        case 'fill': { const parts = args.split(/\s+/); return `Typing "${parts.slice(1).join(' ')}" into ${parts[0]}`; }
+        case 'text': return 'Reading page text';
+        case 'html': return args ? `Reading HTML of ${args}` : 'Reading full page HTML';
+        case 'links': return 'Finding all links on the page';
+        case 'forms': return 'Looking for forms';
+        case 'console': return 'Checking browser console for errors';
+        case 'network': return 'Checking network requests';
+        case 'url': return 'Checking current URL';
+        case 'back': return 'Going back';
+        case 'forward': return 'Going forward';
+        case 'reload': return 'Reloading the page';
+        case 'scroll': return args ? `Scrolling to ${args}` : 'Scrolling down';
+        case 'wait': return `Waiting for ${args}`;
+        case 'inspect': return args ? `Inspecting CSS of ${args}` : 'Getting CSS for last picked element';
+        case 'style': return `Changing CSS: ${args}`;
+        case 'cleanup': return 'Removing page clutter (ads, popups, banners)';
+        case 'prettyscreenshot': return 'Taking a clean screenshot';
+        case 'css': return `Checking CSS property: ${args}`;
+        case 'is': return `Checking if element is ${args}`;
+        case 'diff': return `Comparing ${args}`;
+        case 'responsive': return 'Taking screenshots at mobile, tablet, and desktop sizes';
+        case 'status': return 'Checking browser status';
+        case 'tabs': return 'Listing open tabs';
+        case 'focus': return 'Bringing browser to front';
+        case 'select': return `Selecting option in ${args}`;
+        case 'hover': return `Hovering over ${args}`;
+        case 'viewport': return `Setting viewport to ${args}`;
+        case 'upload': return `Uploading file to ${args.split(/\s+/)[0]}`;
+        default: return `Running browse ${browseCmd} ${args}`.trim();
+      }
+    }
+    if (cmd.includes('git ')) return `Running: ${shorten(cmd)}`;
+    let short = shorten(cmd);
+    return short.length > 100 ? short.slice(0, 100) + '…' : short;
+  }
+
+  if (tool === 'Read' && input.file_path) return `Reading ${shorten(input.file_path)}`;
+  if (tool === 'Edit' && input.file_path) return `Editing ${shorten(input.file_path)}`;
+  if (tool === 'Write' && input.file_path) return `Writing ${shorten(input.file_path)}`;
+  if (tool === 'Grep' && input.pattern) return `Searching for "${input.pattern}"`;
+  if (tool === 'Glob' && input.pattern) return `Finding files matching ${input.pattern}`;
+  try { return shorten(JSON.stringify(input)).slice(0, 80); } catch { return ''; }
+}
+
 // ─── Test setup ──────────────────────────────────────────────────
 
 let tmpDir: string;
@@ -197,3 +265,288 @@ describe('writeToInbox', () => {
     expect(files.length).toBe(2);
   });
 });
+
+// ─── describeToolCall (verbose narration) ────────────────────────
+
+describe('describeToolCall', () => {
+  // Browse navigation commands
+  test('goto → plain English with URL', () => {
+    const result = describeToolCall('Bash', { command: '$B goto https://example.com' });
+    expect(result).toBe('Opening https://example.com');
+  });
+
+  test('goto strips quotes from URL', () => {
+    const result = describeToolCall('Bash', { command: '$B goto "https://example.com"' });
+    expect(result).toBe('Opening https://example.com');
+  });
+
+  test('url → checking current URL', () => {
+    expect(describeToolCall('Bash', { command: '$B url' })).toBe('Checking current URL');
+  });
+
+  test('back/forward/reload → plain English', () => {
+    expect(describeToolCall('Bash', { command: '$B back' })).toBe('Going back');
+    expect(describeToolCall('Bash', { command: '$B forward' })).toBe('Going forward');
+    expect(describeToolCall('Bash', { command: '$B reload' })).toBe('Reloading the page');
+  });
+
+  // Snapshot variants
+  test('snapshot -i → scanning for interactive elements', () => {
+    expect(describeToolCall('Bash', { command: '$B snapshot -i' })).toBe('Scanning for interactive elements');
+  });
+
+  test('snapshot -D → checking what changed', () => {
+    expect(describeToolCall('Bash', { command: '$B snapshot -D' })).toBe('Checking what changed');
+  });
+
+  test('snapshot (plain) → taking a snapshot', () => {
+    expect(describeToolCall('Bash', { command: '$B snapshot' })).toBe('Taking a snapshot of the page');
+  });
+
+  // Interaction commands
+  test('click → clicking element', () => {
+    expect(describeToolCall('Bash', { command: '$B click @e3' })).toBe('Clicking @e3');
+  });
+
+  test('fill → typing into element', () => {
+    expect(describeToolCall('Bash', { command: '$B fill @e4 "hello world"' })).toBe('Typing ""hello world"" into @e4');
+  });
+
+  test('scroll with selector → scrolling to element', () => {
+    expect(describeToolCall('Bash', { command: '$B scroll .footer' })).toBe('Scrolling to .footer');
+  });
+
+  test('scroll without args → scrolling down', () => {
+    expect(describeToolCall('Bash', { command: '$B scroll' })).toBe('Scrolling down');
+  });
+
+  // Reading commands
+  test('text → reading page text', () => {
+    expect(describeToolCall('Bash', { command: '$B text' })).toBe('Reading page text');
+  });
+
+  test('html with selector → reading HTML of element', () => {
+    expect(describeToolCall('Bash', { command: '$B html .header' })).toBe('Reading HTML of .header');
+  });
+
+  test('html without selector → reading full page HTML', () => {
+    expect(describeToolCall('Bash', { command: '$B html' })).toBe('Reading full page HTML');
+  });
+
+  test('links → finding all links', () => {
+    expect(describeToolCall('Bash', { command: '$B links' })).toBe('Finding all links on the page');
+  });
+
+  test('console → checking console', () => {
+    expect(describeToolCall('Bash', { command: '$B console' })).toBe('Checking browser console for errors');
+  });
+
+  // Inspector commands
+  test('inspect with selector → inspecting CSS', () => {
+    expect(describeToolCall('Bash', { command: '$B inspect .header' })).toBe('Inspecting CSS of .header');
+  });
+
+  test('inspect without args → getting last picked element', () => {
+    expect(describeToolCall('Bash', { command: '$B inspect' })).toBe('Getting CSS for last picked element');
+  });
+
+  test('style → changing CSS', () => {
+    expect(describeToolCall('Bash', { command: '$B style .header color red' })).toBe('Changing CSS: .header color red');
+  });
+
+  test('cleanup → removing page clutter', () => {
+    expect(describeToolCall('Bash', { command: '$B cleanup --all' })).toBe('Removing page clutter (ads, popups, banners)');
+  });
+
+  // Visual commands
+  test('screenshot → saving screenshot', () => {
+    expect(describeToolCall('Bash', { command: '$B screenshot /tmp/shot.png' })).toBe('Saving screenshot to /tmp/shot.png');
+  });
+
+  test('screenshot without path', () => {
+    expect(describeToolCall('Bash', { command: '$B screenshot' })).toBe('Saving screenshot');
+  });
+
+  test('responsive → multi-size screenshots', () => {
+    expect(describeToolCall('Bash', { command: '$B responsive' })).toBe('Taking screenshots at mobile, tablet, and desktop sizes');
+  });
+
+  // Non-browse tools
+  test('Read tool → reading file', () => {
+    expect(describeToolCall('Read', { file_path: '/Users/foo/project/src/app.ts' })).toBe('Reading ~/project/src/app.ts');
+  });
+
+  test('Grep tool → searching for pattern', () => {
+    expect(describeToolCall('Grep', { pattern: 'handleClick' })).toBe('Searching for "handleClick"');
+  });
+
+  test('Glob tool → finding files', () => {
+    expect(describeToolCall('Glob', { pattern: '**/*.tsx' })).toBe('Finding files matching **/*.tsx');
+  });
+
+  test('Edit tool → editing file', () => {
+    expect(describeToolCall('Edit', { file_path: '/Users/foo/src/main.ts' })).toBe('Editing ~/src/main.ts');
+  });
+
+  // Edge cases
+  test('null input → empty string', () => {
+    expect(describeToolCall('Bash', null)).toBe('');
+  });
+
+  test('unknown browse command → generic description', () => {
+    expect(describeToolCall('Bash', { command: '$B newtab https://foo.com' })).toContain('newtab');
+  });
+
+  test('non-browse bash → shortened command', () => {
+    expect(describeToolCall('Bash', { command: 'echo hello' })).toBe('echo hello');
+  });
+
+  test('full browse binary path recognized', () => {
+    const result = describeToolCall('Bash', { command: '/Users/garrytan/.claude/skills/gstack/browse/dist/browse goto https://example.com' });
+    expect(result).toBe('Opening https://example.com');
+  });
+
+  test('tab command → switching tab', () => {
+    expect(describeToolCall('Bash', { command: '$B tab 2' })).toContain('tab');
+  });
+});
+
+// ─── Per-tab agent concurrency (source code validation) ──────────
+
+describe('per-tab agent concurrency', () => {
+  const serverSrc = fs.readFileSync(path.join(__dirname, '..', 'src', 'server.ts'), 'utf-8');
+  const agentSrc = fs.readFileSync(path.join(__dirname, '..', 'src', 'sidebar-agent.ts'), 'utf-8');
+
+  test('server has per-tab agent state map', () => {
+    expect(serverSrc).toContain('tabAgents');
+    expect(serverSrc).toContain('TabAgentState');
+    expect(serverSrc).toContain('getTabAgent');
+  });
+
+  test('server returns per-tab agent status in /sidebar-chat', () => {
+    expect(serverSrc).toContain('getTabAgentStatus');
+    expect(serverSrc).toContain('tabAgentStatus');
+  });
+
+  test('spawnClaude accepts forTabId parameter', () => {
+    const spawnFn = serverSrc.slice(
+      serverSrc.indexOf('function spawnClaude('),
+      serverSrc.indexOf('\nfunction ', serverSrc.indexOf('function spawnClaude(') + 1),
+    );
+    expect(spawnFn).toContain('forTabId');
+    expect(spawnFn).toContain('tabState.status');
+  });
+
+  test('sidebar-command endpoint uses per-tab agent state', () => {
+    expect(serverSrc).toContain('msgTabId');
+    expect(serverSrc).toContain('tabState.status');
+    expect(serverSrc).toContain('tabState.queue');
+  });
+
+  test('agent event handler resets per-tab state', () => {
+    expect(serverSrc).toContain('eventTabId');
+    expect(serverSrc).toContain('tabState.status = \'idle\'');
+  });
+
+  test('agent event handler processes per-tab queue', () => {
+    // After agent_done, should process next message from THIS tab's queue
+    expect(serverSrc).toContain('tabState.queue.length > 0');
+    expect(serverSrc).toContain('tabState.queue.shift');
+  });
+
+  test('sidebar-agent uses per-tab processing set', () => {
+    expect(agentSrc).toContain('processingTabs');
+    expect(agentSrc).not.toContain('isProcessing');
+  });
+
+  test('sidebar-agent sends tabId with all events', () => {
+    // sendEvent should accept tabId parameter
+    expect(agentSrc).toContain('async function sendEvent(event: Record<string, any>, tabId?: number)');
+    // askClaude should extract tabId from queue entry
+    expect(agentSrc).toContain('const { prompt, args, stateFile, cwd, tabId }');
+  });
+
+  test('sidebar-agent allows concurrent agents across tabs', () => {
+    // poll() should not block globally — it should check per-tab
+    expect(agentSrc).toContain('processingTabs.has(tid)');
+    // askClaude should be fire-and-forget (no await blocking the loop)
+    expect(agentSrc).toContain('askClaude(entry).catch');
+  });
+
+  test('queue entries include tabId', () => {
+    const spawnFn = serverSrc.slice(
+      serverSrc.indexOf('function spawnClaude('),
+      serverSrc.indexOf('\nfunction ', serverSrc.indexOf('function spawnClaude(') + 1),
+    );
+    expect(spawnFn).toContain('tabId: agentTabId');
+  });
+
+  test('health check monitors all per-tab agents', () => {
+    expect(serverSrc).toContain('for (const [tid, state] of tabAgents)');
+  });
+});
+
+describe('BROWSE_TAB tab pinning (cross-tab isolation)', () => {
+  const serverSrc = fs.readFileSync(path.join(__dirname, '..', 'src', 'server.ts'), 'utf-8');
+  const agentSrc = fs.readFileSync(path.join(__dirname, '..', 'src', 'sidebar-agent.ts'), 'utf-8');
+  const cliSrc = fs.readFileSync(path.join(__dirname, '..', 'src', 'cli.ts'), 'utf-8');
+
+  test('sidebar-agent passes BROWSE_TAB env var to claude process', () => {
+    // The env block should include BROWSE_TAB set to the tab ID
+    expect(agentSrc).toContain('BROWSE_TAB');
+    expect(agentSrc).toContain('String(tid)');
+  });
+
+  test('CLI reads BROWSE_TAB and sends tabId in command body', () => {
+    expect(cliSrc).toContain('process.env.BROWSE_TAB');
+    expect(cliSrc).toContain('tabId: parseInt(browseTab');
+  });
+
+  test('handleCommand accepts tabId from request body', () => {
+    const handleFn = serverSrc.slice(
+      serverSrc.indexOf('async function handleCommand('),
+      serverSrc.indexOf('\nasync function ', serverSrc.indexOf('async function handleCommand(') + 1) > 0
+        ? serverSrc.indexOf('\nasync function ', serverSrc.indexOf('async function handleCommand(') + 1)
+        : serverSrc.indexOf('\n// ', serverSrc.indexOf('async function handleCommand(') + 200),
+    );
+    // Should destructure tabId from body
+    expect(handleFn).toContain('tabId');
+    // Should save and restore the active tab
+    expect(handleFn).toContain('savedTabId');
+    expect(handleFn).toContain('browserManager.switchTab(tabId)');
+  });
+
+  test('handleCommand restores active tab after command (success path)', () => {
+    // On success, should restore savedTabId
+    const handleFn = serverSrc.slice(
+      serverSrc.indexOf('async function handleCommand('),
+      serverSrc.length,
+    );
+    // Count restore calls — should appear in both success and error paths
+    const restoreCount = (handleFn.match(/browserManager\.switchTab\(savedTabId\)/g) || []).length;
+    expect(restoreCount).toBeGreaterThanOrEqual(2); // success + error paths
+  });
+
+  test('handleCommand restores active tab on error path', () => {
+    // The catch block should also restore
+    const catchBlock = serverSrc.slice(
+      serverSrc.indexOf('} catch (err: any) {', serverSrc.indexOf('async function handleCommand(')),
+    );
+    expect(catchBlock).toContain('switchTab(savedTabId)');
+  });
+
+  test('tab pinning only activates when tabId is provided', () => {
+    const handleFn = serverSrc.slice(
+      serverSrc.indexOf('async function handleCommand('),
+      serverSrc.indexOf('try {', serverSrc.indexOf('async function handleCommand(') + 1),
+    );
+    // Should check tabId is not undefined/null before switching
+    expect(handleFn).toContain('tabId !== undefined');
+    expect(handleFn).toContain('tabId !== null');
+  });
+
+  test('CLI only sends tabId when BROWSE_TAB is set', () => {
+    // Should conditionally include tabId in the body
+    expect(cliSrc).toContain('browseTab ? { tabId:');
+  });
+});
diff --git a/browse/test/sidebar-ux.test.ts b/browse/test/sidebar-ux.test.ts
new file mode 100644
index 00000000..bc595e7a
--- /dev/null
+++ b/browse/test/sidebar-ux.test.ts
@@ -0,0 +1,676 @@
+/**
+ * Tests for sidebar UX changes:
+ * - System prompt does not bake in page URL (navigation fix)
+ * - --resume is never used (stale context fix)
+ * - /sidebar-chat response includes agentStatus
+ * - Sidebar HTML has updated banner, placeholder, stop button
+ * - Narration instructions present in system prompt
+ */
+
+import { describe, test, expect } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+
+const ROOT = path.resolve(__dirname, '..');
+
+// ─── System prompt tests (server.ts spawnClaude) ─────────────────
+
+describe('sidebar system prompt (server.ts)', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  test('system prompt does not bake in page URL', () => {
+    // The old prompt had: `The user is currently viewing: ${pageUrl}`
+    // The new prompt should NOT contain this pattern
+    // Extract the systemPrompt array from spawnClaude
+    const promptSection = serverSrc.slice(
+      serverSrc.indexOf('const systemPrompt = ['),
+      serverSrc.indexOf("].join('\\n');", serverSrc.indexOf('const systemPrompt = [')) + 15,
+    );
+    expect(promptSection).not.toContain('currently viewing');
+    expect(promptSection).not.toContain('${pageUrl}');
+  });
+
+  test('system prompt tells agent to check URL before acting', () => {
+    const promptSection = serverSrc.slice(
+      serverSrc.indexOf('const systemPrompt = ['),
+      serverSrc.indexOf("].join('\\n');", serverSrc.indexOf('const systemPrompt = [')) + 15,
+    );
+    expect(promptSection).toContain('NEVER');
+    expect(promptSection).toContain('navigate back');
+    expect(promptSection).toContain('NEVER assume');
+    expect(promptSection).toContain('url`');
+  });
+
+  test('system prompt includes narration instructions', () => {
+    const promptSection = serverSrc.slice(
+      serverSrc.indexOf('const systemPrompt = ['),
+      serverSrc.indexOf("].join('\\n');", serverSrc.indexOf('const systemPrompt = [')) + 15,
+    );
+    expect(promptSection).toContain('Narrate');
+    expect(promptSection).toContain('plain English');
+  });
+
+  test('--resume is never used in spawnClaude args', () => {
+    // Extract the spawnClaude function
+    const fnStart = serverSrc.indexOf('function spawnClaude(');
+    const fnEnd = serverSrc.indexOf('\nfunction ', fnStart + 1);
+    const fnBody = serverSrc.slice(fnStart, fnEnd);
+    // Should not push --resume to args
+    expect(fnBody).not.toContain("'--resume'");
+    expect(fnBody).not.toContain('"--resume"');
+  });
+
+  test('system prompt includes inspect and style commands', () => {
+    const promptSection = serverSrc.slice(
+      serverSrc.indexOf('const systemPrompt = ['),
+      serverSrc.indexOf("].join('\\n');", serverSrc.indexOf('const systemPrompt = [')) + 15,
+    );
+    expect(promptSection).toContain('inspect');
+    expect(promptSection).toContain('style');
+    expect(promptSection).toContain('cleanup');
+  });
+});
+
+// ─── /sidebar-chat response includes agentStatus ─────────────────
+
+describe('/sidebar-chat agentStatus', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  test('sidebar-chat response includes agentStatus field', () => {
+    // Find the GET /sidebar-chat handler — look for the data response, not the auth error
+    const handlerStart = serverSrc.indexOf("url.pathname === '/sidebar-chat'");
+    // Find the response that returns entries + total (skip the auth error response)
+    const entriesResponse = serverSrc.indexOf('{ entries, total', handlerStart);
+    expect(entriesResponse).toBeGreaterThan(handlerStart);
+    const responseLine = serverSrc.slice(entriesResponse, entriesResponse + 100);
+    expect(responseLine).toContain('agentStatus');
+  });
+});
+
+// ─── Sidebar HTML tests ──────────────────────────────────────────
+
+describe('sidebar HTML (sidepanel.html)', () => {
+  const html = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.html'), 'utf-8');
+
+  test('banner says "Browser co-pilot" not "Standalone mode"', () => {
+    expect(html).toContain('Browser co-pilot');
+    expect(html).not.toContain('Standalone mode');
+  });
+
+  test('input placeholder says "Ask about this page"', () => {
+    expect(html).toContain('Ask about this page');
+    expect(html).not.toContain('Message Claude Code');
+  });
+
+  test('stop button exists with id stop-agent-btn', () => {
+    expect(html).toContain('id="stop-agent-btn"');
+    expect(html).toContain('class="stop-btn"');
+  });
+
+  test('stop button is hidden by default', () => {
+    // The stop button should have style="display: none;" initially
+    const stopBtnMatch = html.match(/id="stop-agent-btn"[^>]*/);
+    expect(stopBtnMatch).not.toBeNull();
+    expect(stopBtnMatch![0]).toContain('display: none');
+  });
+});
+
+// ─── Sidebar JS tests ───────────────────────────────────────────
+
+describe('sidebar JS (sidepanel.js)', () => {
+  const js = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.js'), 'utf-8');
+
+  test('stopAgent function exists', () => {
+    expect(js).toContain('async function stopAgent()');
+  });
+
+  test('stopAgent calls /sidebar-agent/stop endpoint', () => {
+    expect(js).toContain('/sidebar-agent/stop');
+  });
+
+  test('stop button click handler is wired up', () => {
+    expect(js).toContain("getElementById('stop-agent-btn')");
+    expect(js).toContain('stopAgent');
+  });
+
+  test('updateStopButton function exists', () => {
+    expect(js).toContain('function updateStopButton(');
+  });
+
+  test('agent_start shows stop button', () => {
+    // Find the agent_start handler and verify it calls updateStopButton(true)
+    const startHandler = js.slice(
+      js.indexOf("entry.type === 'agent_start'"),
+      js.indexOf("entry.type === 'agent_done'"),
+    );
+    expect(startHandler).toContain('updateStopButton(true)');
+  });
+
+  test('agent_done hides stop button', () => {
+    const doneHandler = js.slice(
+      js.indexOf("entry.type === 'agent_done'"),
+      js.indexOf("entry.type === 'agent_error'"),
+    );
+    expect(doneHandler).toContain('updateStopButton(false)');
+  });
+
+  test('agent_error hides stop button', () => {
+    const errorIdx = js.indexOf("entry.type === 'agent_error'");
+    const errorHandler = js.slice(errorIdx, errorIdx + 500);
+    expect(errorHandler).toContain('updateStopButton(false)');
+  });
+
+  test('orphaned thinking cleanup checks agentStatus from server', () => {
+    // After polling, if agentStatus !== processing, thinking dots are removed
+    expect(js).toContain("data.agentStatus !== 'processing'");
+  });
+
+  test('orphaned thinking cleanup adds (session ended) notice', () => {
+    expect(js).toContain('(session ended)');
+  });
+
+  test('sendMessage renders user bubble + thinking dots optimistically', () => {
+    // sendMessage should create user bubble and agent-thinking BEFORE the server responds
+    const sendFn = js.slice(js.indexOf('async function sendMessage()'), js.indexOf('async function sendMessage()') + 2000);
+    expect(sendFn).toContain('chat-bubble user');
+    expect(sendFn).toContain('agent-thinking');
+    expect(sendFn).toContain('lastOptimisticMsg');
+  });
+
+  test('fast polling during agent execution (300ms), slow when idle (1000ms)', () => {
+    expect(js).toContain('FAST_POLL_MS');
+    expect(js).toContain('SLOW_POLL_MS');
+    expect(js).toContain('startFastPoll');
+    expect(js).toContain('stopFastPoll');
+    // Fast = 300ms
+    expect(js).toContain('300');
+    // Slow = 1000ms
+    expect(js).toContain('1000');
+  });
+
+  test('agent_done calls stopFastPoll', () => {
+    const doneHandler = js.slice(
+      js.indexOf("entry.type === 'agent_done'"),
+      js.indexOf("entry.type === 'agent_error'"),
+    );
+    expect(doneHandler).toContain('stopFastPoll');
+  });
+
+  test('duplicate user bubble prevention via lastOptimisticMsg', () => {
+    expect(js).toContain('lastOptimisticMsg');
+    // When polled message matches optimistic, skip rendering
+    expect(js).toContain('lastOptimisticMsg === entry.message');
+  });
+});
+
+// ─── Sidebar agent queue poll (sidebar-agent.ts) ─────────────────
+
+describe('sidebar agent queue poll (sidebar-agent.ts)', () => {
+  const agentSrc = fs.readFileSync(path.join(ROOT, 'src', 'sidebar-agent.ts'), 'utf-8');
+
+  test('queue poll interval is 200ms or less for fast TTFO', () => {
+    const match = agentSrc.match(/const POLL_MS\s*=\s*(\d+)/);
+    expect(match).not.toBeNull();
+    const pollMs = parseInt(match![1], 10);
+    expect(pollMs).toBeLessThanOrEqual(200);
+  });
+});
+
+// ─── System prompt size (TTFO optimization) ──────────────────────
+
+describe('system prompt size', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  test('system prompt is compact (under 20 lines)', () => {
+    const start = serverSrc.indexOf('const systemPrompt = [');
+    const end = serverSrc.indexOf("].join('\\n');", start);
+    const promptBlock = serverSrc.slice(start, end);
+    const lines = promptBlock.split('\n').length;
+    // Compact prompt = fewer input tokens = faster first response
+    // Slightly higher limit because of per-tab instruction line
+    expect(lines).toBeLessThan(20);
+  });
+
+  test('system prompt does not contain verbose narration examples', () => {
+    // We trimmed examples to reduce token count. The agent gets the
+    // instruction to narrate, not 6 examples of how.
+    const start = serverSrc.indexOf('const systemPrompt = [');
+    const end = serverSrc.indexOf("].join('\\n');", start);
+    const promptBlock = serverSrc.slice(start, end);
+    expect(promptBlock).not.toContain('Examples of good narration');
+    expect(promptBlock).not.toContain('I can see a login form');
+  });
+});
+
+// ─── TTFO latency chain invariants ──────────────────────────────
+
+describe('TTFO latency chain', () => {
+  const js = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.js'), 'utf-8');
+  const agentSrc = fs.readFileSync(path.join(ROOT, 'src', 'sidebar-agent.ts'), 'utf-8');
+
+  test('optimistic render happens BEFORE chrome.runtime.sendMessage', () => {
+    // In sendMessage(), the bubble + thinking dots must be created
+    // before the async POST to the server
+    const sendFn = js.slice(
+      js.indexOf('async function sendMessage()'),
+      js.indexOf('async function sendMessage()') + 3000,
+    );
+    const optimisticIdx = sendFn.indexOf('agent-thinking');
+    const sendIdx = sendFn.indexOf('chrome.runtime.sendMessage');
+    expect(optimisticIdx).toBeGreaterThan(0);
+    expect(sendIdx).toBeGreaterThan(0);
+    expect(optimisticIdx).toBeLessThan(sendIdx);
+  });
+
+  test('sendMessage calls startFastPoll before server request', () => {
+    const sendFn = js.slice(
+      js.indexOf('async function sendMessage()'),
+      js.indexOf('async function sendMessage()') + 3000,
+    );
+    const fastPollIdx = sendFn.indexOf('startFastPoll');
+    const sendIdx = sendFn.indexOf('chrome.runtime.sendMessage');
+    expect(fastPollIdx).toBeGreaterThan(0);
+    expect(fastPollIdx).toBeLessThan(sendIdx);
+  });
+
+  test('agent_start from server does not duplicate thinking dots', () => {
+    // When we already showed dots optimistically, agent_start from
+    // the poll should skip creating a second set
+    const startHandler = js.slice(
+      js.indexOf("entry.type === 'agent_start'"),
+      js.indexOf("entry.type === 'agent_done'"),
+    );
+    expect(startHandler).toContain('agent-thinking');
+    // Should check if thinking already exists and skip
+    expect(startHandler).toContain("getElementById('agent-thinking')");
+  });
+
+  test('FAST_POLL_MS is strictly less than SLOW_POLL_MS', () => {
+    const fastMatch = js.match(/FAST_POLL_MS\s*=\s*(\d+)/);
+    const slowMatch = js.match(/SLOW_POLL_MS\s*=\s*(\d+)/);
+    expect(fastMatch).not.toBeNull();
+    expect(slowMatch).not.toBeNull();
+    expect(parseInt(fastMatch![1], 10)).toBeLessThan(parseInt(slowMatch![1], 10));
+  });
+
+  test('stopAgent also calls stopFastPoll', () => {
+    const stopFn = js.slice(
+      js.indexOf('async function stopAgent()'),
+      js.indexOf('async function stopAgent()') + 800,
+    );
+    expect(stopFn).toContain('stopFastPoll');
+  });
+});
+
+// ─── Browser tab bar ────────────────────────────────────────────
+
+describe('browser tab bar (server.ts)', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  test('/sidebar-tabs endpoint exists', () => {
+    expect(serverSrc).toContain("/sidebar-tabs'");
+    expect(serverSrc).toContain('getTabListWithTitles');
+  });
+
+  test('/sidebar-tabs/switch endpoint exists', () => {
+    expect(serverSrc).toContain("/sidebar-tabs/switch'");
+    expect(serverSrc).toContain('switchTab');
+  });
+
+  test('/sidebar-tabs requires auth', () => {
+    // Find the handler and verify auth check
+    const handlerIdx = serverSrc.indexOf("/sidebar-tabs'");
+    const handlerBlock = serverSrc.slice(handlerIdx, handlerIdx + 300);
+    expect(handlerBlock).toContain('validateAuth');
+  });
+});
+
+describe('browser tab bar (sidepanel.js)', () => {
+  const js = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.js'), 'utf-8');
+
+  test('pollTabs function exists and calls /sidebar-tabs', () => {
+    expect(js).toContain('async function pollTabs()');
+    expect(js).toContain('/sidebar-tabs');
+  });
+
+  test('renderTabBar function exists', () => {
+    expect(js).toContain('function renderTabBar(tabs)');
+  });
+
+  test('tab bar hidden when only 1 tab', () => {
+    const renderFn = js.slice(
+      js.indexOf('function renderTabBar('),
+      js.indexOf('function renderTabBar(') + 600,
+    );
+    expect(renderFn).toContain('tabs.length <= 1');
+    expect(renderFn).toContain("display = 'none'");
+  });
+
+  test('switchBrowserTab calls /sidebar-tabs/switch', () => {
+    expect(js).toContain('async function switchBrowserTab(');
+    expect(js).toContain('/sidebar-tabs/switch');
+  });
+
+  test('tab polling interval is set on connection', () => {
+    expect(js).toContain('tabPollInterval');
+    expect(js).toContain('setInterval(pollTabs');
+  });
+
+  test('tab polling cleaned up on disconnect', () => {
+    expect(js).toContain('clearInterval(tabPollInterval)');
+  });
+
+  test('only re-renders when tabs change (diff check)', () => {
+    expect(js).toContain('lastTabJson');
+    expect(js).toContain('json === lastTabJson');
+  });
+});
+
+describe('browser tab bar (sidepanel.html)', () => {
+  const html = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.html'), 'utf-8');
+
+  test('browser-tabs container exists', () => {
+    expect(html).toContain('id="browser-tabs"');
+  });
+
+  test('browser-tabs hidden by default', () => {
+    const match = html.match(/id="browser-tabs"[^>]*/);
+    expect(match).not.toBeNull();
+    expect(match![0]).toContain('display:none');
+  });
+});
+
+// ─── Bidirectional tab sync ──────────────────────────────────────
+
+describe('sidebar→browser tab switch', () => {
+  const bmSrc = fs.readFileSync(path.join(ROOT, 'src', 'browser-manager.ts'), 'utf-8');
+
+  test('switchTab calls bringToFront so browser visually switches', () => {
+    const switchFn = bmSrc.slice(
+      bmSrc.indexOf('switchTab(id: number)'),
+      bmSrc.indexOf('switchTab(id: number)') + 400,
+    );
+    expect(switchFn).toContain('bringToFront');
+  });
+});
+
+describe('browser→sidebar tab sync', () => {
+  const bmSrc = fs.readFileSync(path.join(ROOT, 'src', 'browser-manager.ts'), 'utf-8');
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+  const js = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.js'), 'utf-8');
+
+  test('syncActiveTabByUrl method exists on BrowserManager', () => {
+    expect(bmSrc).toContain('syncActiveTabByUrl(activeUrl: string)');
+  });
+
+  test('syncActiveTabByUrl updates activeTabId when URL matches a different tab', () => {
+    const fn = bmSrc.slice(
+      bmSrc.indexOf('syncActiveTabByUrl('),
+      bmSrc.indexOf('syncActiveTabByUrl(') + 1200,
+    );
+    expect(fn).toContain('this.activeTabId = id');
+    // Exact match
+    expect(fn).toContain('pageUrl === activeUrl');
+    // Fuzzy match (origin+pathname)
+    expect(fn).toContain('activeOriginPath');
+    expect(fn).toContain('fuzzyId');
+  });
+
+  test('context.on("page") tracks user-created tabs', () => {
+    expect(bmSrc).toContain("context.on('page'");
+    expect(bmSrc).toContain('this.pages.set(id, page)');
+    // Should log when new tab detected
+    expect(bmSrc).toContain('New tab detected');
+  });
+
+  test('page close handler removes tab from pages map', () => {
+    expect(bmSrc).toContain("page.on('close'");
+    expect(bmSrc).toContain('this.pages.delete(id)');
+    expect(bmSrc).toContain('Tab closed');
+  });
+
+  test('syncActiveTabByUrl skips when only 1 tab (no ambiguity)', () => {
+    const fn = bmSrc.slice(
+      bmSrc.indexOf('syncActiveTabByUrl('),
+      bmSrc.indexOf('syncActiveTabByUrl(') + 600,
+    );
+    expect(fn).toContain('this.pages.size <= 1');
+  });
+
+  test('/sidebar-tabs reads activeUrl param and calls syncActiveTabByUrl', () => {
+    const handler = serverSrc.slice(
+      serverSrc.indexOf("/sidebar-tabs'"),
+      serverSrc.indexOf("/sidebar-tabs'") + 500,
+    );
+    expect(handler).toContain("get('activeUrl')");
+    expect(handler).toContain('syncActiveTabByUrl');
+  });
+
+  test('/sidebar-command syncs activeTabUrl BEFORE reading tabId', () => {
+    // The server must call syncActiveTabByUrl before getActiveTabId
+    // so the agent targets the correct tab
+    const cmdIdx = serverSrc.indexOf("url.pathname === '/sidebar-command'");
+    const handler = serverSrc.slice(cmdIdx, cmdIdx + 1200);
+    const syncIdx = handler.indexOf('syncActiveTabByUrl');
+    const getIdIdx = handler.indexOf('getActiveTabId');
+    expect(syncIdx).toBeGreaterThan(0);
+    expect(getIdIdx).toBeGreaterThan(syncIdx); // sync happens BEFORE reading ID
+  });
+
+  test('background.js listens for chrome.tabs.onActivated', () => {
+    const bgSrc = fs.readFileSync(path.join(ROOT, '..', 'extension', 'background.js'), 'utf-8');
+    expect(bgSrc).toContain('chrome.tabs.onActivated.addListener');
+    expect(bgSrc).toContain('browserTabActivated');
+  });
+
+  test('sidepanel handles browserTabActivated message instantly', () => {
+    expect(js).toContain("msg.type === 'browserTabActivated'");
+    // Should call switchChatTab for instant context swap
+    expect(js).toContain('switchChatTab');
+  });
+
+  test('pollTabs sends Chrome active tab URL to server', () => {
+    const pollFn = js.slice(
+      js.indexOf('async function pollTabs()'),
+      js.indexOf('async function pollTabs()') + 800,
+    );
+    expect(pollFn).toContain('chrome.tabs.query');
+    expect(pollFn).toContain('activeUrl=');
+  });
+});
+
+describe('browser tab bar (sidepanel.css)', () => {
+  const css = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.css'), 'utf-8');
+
+  test('browser-tabs styles exist', () => {
+    expect(css).toContain('.browser-tabs');
+    expect(css).toContain('.browser-tab');
+    expect(css).toContain('.browser-tab.active');
+  });
+
+  test('tab bar is horizontally scrollable', () => {
+    const barStyle = css.slice(
+      css.indexOf('.browser-tabs {'),
+      css.indexOf('}', css.indexOf('.browser-tabs {')) + 1,
+    );
+    expect(barStyle).toContain('overflow-x: auto');
+  });
+
+  test('active tab is visually distinct', () => {
+    const activeStyle = css.slice(
+      css.indexOf('.browser-tab.active {'),
+      css.indexOf('}', css.indexOf('.browser-tab.active {')) + 1,
+    );
+    expect(activeStyle).toContain('--bg-surface');
+    expect(activeStyle).toContain('--text-body');
+  });
+});
+
+// ─── Event relay (processAgentEvent) ────────────────────────────
+
+describe('processAgentEvent handles sidebar-agent event types', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  // Extract processAgentEvent function body
+  const fnStart = serverSrc.indexOf('function processAgentEvent(');
+  const fnEnd = serverSrc.indexOf('\nfunction ', fnStart + 1);
+  const fnBody = serverSrc.slice(fnStart, fnEnd > fnStart ? fnEnd : fnStart + 2000);
+
+  test('handles tool_use events directly (not raw Claude stream format)', () => {
+    // Must handle { type: 'tool_use', tool, input } from sidebar-agent
+    expect(fnBody).toContain("event.type === 'tool_use'");
+    expect(fnBody).toContain('event.tool');
+    expect(fnBody).toContain('event.input');
+  });
+
+  test('handles text_delta events directly', () => {
+    expect(fnBody).toContain("event.type === 'text_delta'");
+    expect(fnBody).toContain('event.text');
+  });
+
+  test('handles text events directly', () => {
+    expect(fnBody).toContain("event.type === 'text'");
+  });
+
+  test('handles result events', () => {
+    expect(fnBody).toContain("event.type === 'result'");
+  });
+
+  test('handles agent_error events', () => {
+    expect(fnBody).toContain("event.type === 'agent_error'");
+    expect(fnBody).toContain('event.error');
+  });
+
+  test('does NOT re-parse raw Claude stream events (no content_block_start)', () => {
+    // sidebar-agent.ts already transforms these. Server should not duplicate.
+    expect(fnBody).not.toContain('content_block_start');
+    expect(fnBody).not.toContain('content_block_delta');
+    expect(fnBody).not.toContain("event.type === 'assistant'");
+  });
+
+  test('all event types call addChatEntry with role: agent', () => {
+    // Every addChatEntry in processAgentEvent should have role: 'agent'
+    const addCalls = fnBody.match(/addChatEntry\(\{[^}]+\}\)/g) || [];
+    for (const call of addCalls) {
+      expect(call).toContain("role: 'agent'");
+    }
+  });
+});
+
+// ─── Per-tab chat context ────────────────────────────────────────
+
+describe('per-tab chat context (server.ts)', () => {
+  const serverSrc = fs.readFileSync(path.join(ROOT, 'src', 'server.ts'), 'utf-8');
+
+  test('/sidebar-chat accepts tabId query param', () => {
+    const handler = serverSrc.slice(
+      serverSrc.indexOf("/sidebar-chat'"),
+      serverSrc.indexOf("/sidebar-chat'") + 600,
+    );
+    expect(handler).toContain('tabId');
+  });
+
+  test('addChatEntry takes a tabId parameter', () => {
+    // addChatEntry should route entries to the correct tab's buffer
+    expect(serverSrc).toContain('tabId');
+    // Look for tabId in addChatEntry function
+    const fnIdx = serverSrc.indexOf('function addChatEntry(');
+    if (fnIdx > -1) {
+      const fnBody = serverSrc.slice(fnIdx, fnIdx + 300);
+      expect(fnBody).toContain('tabId');
+    }
+  });
+
+  test('spawnClaude passes active tab ID to queue entry', () => {
+    const spawnFn = serverSrc.slice(
+      serverSrc.indexOf('function spawnClaude('),
+      serverSrc.indexOf('\nfunction ', serverSrc.indexOf('function spawnClaude(') + 1),
+    );
+    expect(spawnFn).toContain('tabId');
+  });
+
+  test('tab isolation uses BROWSE_TAB env var instead of system prompt hack', () => {
+    const agentSrc = fs.readFileSync(path.join(ROOT, 'src', 'sidebar-agent.ts'), 'utf-8');
+    // Agent passes BROWSE_TAB env var to claude (not a system prompt instruction)
+    expect(agentSrc).toContain('BROWSE_TAB');
+    // Server handleCommand reads tabId from body and pins to that tab
+    expect(serverSrc).toContain('savedTabId');
+    expect(serverSrc).toContain('switchTab(tabId)');
+  });
+});
+
+describe('per-tab chat context (sidepanel.js)', () => {
+  const js = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.js'), 'utf-8');
+
+  test('tracks activeTabId for chat context', () => {
+    expect(js).toContain('activeTabId');
+  });
+
+  test('pollChat sends tabId to server', () => {
+    const pollFn = js.slice(
+      js.indexOf('async function pollChat()'),
+      js.indexOf('async function pollChat()') + 600,
+    );
+    expect(pollFn).toContain('tabId');
+  });
+
+  test('switching tabs swaps displayed chat', () => {
+    // When tab changes, old chat is saved and new tab's chat is shown
+    expect(js).toContain('switchChatTab');
+  });
+
+  test('switchChatTab saves current tab DOM and restores new tab', () => {
+    const fn = js.slice(
+      js.indexOf('function switchChatTab('),
+      js.indexOf('function switchChatTab(') + 800,
+    );
+    expect(fn).toContain('chatDomByTab');
+    expect(fn).toContain('innerHTML');
+  });
+
+  test('sendMessage includes tabId in message', () => {
+    const sendFn = js.slice(
+      js.indexOf('async function sendMessage()'),
+      js.indexOf('async function sendMessage()') + 2000,
+    );
+    expect(sendFn).toContain('tabId');
+    expect(sendFn).toContain('sidebarActiveTabId');
+  });
+});
+
+// ─── Sidebar CSS tests ──────────────────────────────────────────
+
+describe('sidebar CSS (sidepanel.css)', () => {
+  const css = fs.readFileSync(path.join(ROOT, '..', 'extension', 'sidepanel.css'), 'utf-8');
+
+  test('stop button style exists', () => {
+    expect(css).toContain('.stop-btn');
+  });
+
+  test('stop button uses error color', () => {
+    const stopBtnSection = css.slice(
+      css.indexOf('.stop-btn {'),
+      css.indexOf('}', css.indexOf('.stop-btn {')) + 1,
+    );
+    expect(stopBtnSection).toContain('--error');
+  });
+
+  test('experimental-banner no longer uses amber warning colors', () => {
+    const bannerSection = css.slice(
+      css.indexOf('.experimental-banner {'),
+      css.indexOf('}', css.indexOf('.experimental-banner {')) + 1,
+    );
+    // Should not be amber/warning anymore
+    expect(bannerSection).not.toContain('245, 158, 11, 0.15');
+    expect(bannerSection).not.toContain('#F59E0B');
+  });
+
+  test('tool description uses system font not mono', () => {
+    const toolSection = css.slice(
+      css.indexOf('.agent-tool {'),
+      css.indexOf('}', css.indexOf('.agent-tool {')) + 1,
+    );
+    expect(toolSection).toContain('font-system');
+    expect(toolSection).not.toContain('font-mono');
+  });
+});