fix: remove auth token from /health, secure extension bootstrap (CRITICAL-02 + HIGH-03)

- Remove token from /health response (was leaked to any localhost process)
- Write .auth.json to extension dir for Manifest V3 bootstrap
- sidebar-agent reads token from state file via BROWSE_STATE_FILE env var
- Remove getToken handler from extension (token via health broadcast)
- Extension loads token before first health poll to prevent race condition

browse/src/browser-manager.ts

@@ -211,7 +211,7 @@ export class BrowserManager {
    * The browser launches headed with a visible window — the user sees
    * every action Claude takes in real time.
    */
-  async launchHeaded(): Promise<void> {
+  async launchHeaded(authToken?: string): Promise<void> {
     // Clear old state before repopulating
     this.pages.clear();
     this.refMap.clear();
@@ -223,6 +223,17 @@ export class BrowserManager {
     if (extensionPath) {
       launchArgs.push(`--disable-extensions-except=${extensionPath}`);
       launchArgs.push(`--load-extension=${extensionPath}`);
+      // Write auth token for extension bootstrap (read via chrome.runtime.getURL)
+      if (authToken) {
+        const fs = require('fs');
+        const path = require('path');
+        const authFile = path.join(extensionPath, '.auth.json');
+        try {
+          fs.writeFileSync(authFile, JSON.stringify({ token: authToken }), { mode: 0o600 });
+        } catch (err: any) {
+          console.warn(`[browse] Could not write .auth.json: ${err.message}`);
+        }
+      }
     }
 
     // Launch headed Chromium via Playwright's persistent context.
@@ -751,6 +762,20 @@ export class BrowserManager {
       if (extensionPath) {
         launchArgs.push(`--disable-extensions-except=${extensionPath}`);
         launchArgs.push(`--load-extension=${extensionPath}`);
+        // Write auth token for extension bootstrap during handoff
+        if (this.serverPort) {
+          try {
+            const { resolveConfig } = require('./config');
+            const config = resolveConfig();
+            const stateFile = path.join(config.stateDir, 'browse.json');
+            if (fs.existsSync(stateFile)) {
+              const stateData = JSON.parse(fs.readFileSync(stateFile, 'utf-8'));
+              if (stateData.token) {
+                fs.writeFileSync(path.join(extensionPath, '.auth.json'), JSON.stringify({ token: stateData.token }), { mode: 0o600 });
+              }
+            }
+          } catch {}
+        }
         console.log(`[browse] Handoff: loading extension from ${extensionPath}`);
       } else {
         console.log('[browse] Handoff: extension not found — headed mode without side panel');