refactor: harden browser relay CDP flows

assets/chrome-extension/background-utils.js

@@ -46,3 +46,19 @@ export function isRetryableReconnectError(err) {
   }
   return true;
 }
+
+export function isMissingTabError(err) {
+  const message = (err instanceof Error ? err.message : String(err || "")).toLowerCase();
+  return (
+    message.includes("no tab with id") ||
+    message.includes("no tab with given id") ||
+    message.includes("tab not found")
+  );
+}
+
+export function isLastRemainingTab(allTabs, tabIdToClose) {
+  if (!Array.isArray(allTabs)) {
+    return true;
+  }
+  return allTabs.filter((tab) => tab && tab.id !== tabIdToClose).length === 0;
+}

assets/chrome-extension/background.js

@@ -1,4 +1,10 @@
-import { buildRelayWsUrl, isRetryableReconnectError, reconnectDelayMs } from './background-utils.js'
+import {
+  buildRelayWsUrl,
+  isLastRemainingTab,
+  isMissingTabError,
+  isRetryableReconnectError,
+  reconnectDelayMs,
+} from './background-utils.js'
 
 const DEFAULT_PORT = 18792
 
@@ -41,6 +47,9 @@ const reattachPending = new Set()
 let reconnectAttempt = 0
 let reconnectTimer = null
 
+const TAB_VALIDATION_ATTEMPTS = 2
+const TAB_VALIDATION_RETRY_DELAY_MS = 1000
+
 function nowStack() {
   try {
     return new Error().stack || ''
@@ -49,6 +58,37 @@ function nowStack() {
   }
 }
 
+function sleep(ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms))
+}
+
+async function validateAttachedTab(tabId) {
+  try {
+    await chrome.tabs.get(tabId)
+  } catch {
+    return false
+  }
+
+  for (let attempt = 0; attempt < TAB_VALIDATION_ATTEMPTS; attempt++) {
+    try {
+      await chrome.debugger.sendCommand({ tabId }, 'Runtime.evaluate', {
+        expression: '1',
+        returnByValue: true,
+      })
+      return true
+    } catch (err) {
+      if (isMissingTabError(err)) {
+        return false
+      }
+      if (attempt < TAB_VALIDATION_ATTEMPTS - 1) {
+        await sleep(TAB_VALIDATION_RETRY_DELAY_MS)
+      }
+    }
+  }
+
+  return false
+}
+
 async function getRelayPort() {
   const stored = await chrome.storage.local.get(['relayPort'])
   const raw = stored.relayPort
@@ -108,15 +148,11 @@ async function rehydrateState() {
       tabBySession.set(entry.sessionId, entry.tabId)
       setBadge(entry.tabId, 'on')
     }
-    // Phase 2: validate asynchronously, remove dead tabs.
+    // Retry once so transient busy/navigation states do not permanently drop
+    // a still-attached tab after a service worker restart.
     for (const entry of entries) {
-      try {
-        await chrome.tabs.get(entry.tabId)
-        await chrome.debugger.sendCommand({ tabId: entry.tabId }, 'Runtime.evaluate', {
-          expression: '1',
-          returnByValue: true,
-        })
-      } catch {
+      const valid = await validateAttachedTab(entry.tabId)
+      if (!valid) {
         tabs.delete(entry.tabId)
         tabBySession.delete(entry.sessionId)
         setBadge(entry.tabId, 'off')
@@ -259,13 +295,10 @@ async function reannounceAttachedTabs() {
   for (const [tabId, tab] of tabs.entries()) {
     if (tab.state !== 'connected' || !tab.sessionId || !tab.targetId) continue
 
-    // Verify debugger is still attached.
-    try {
-      await chrome.debugger.sendCommand({ tabId }, 'Runtime.evaluate', {
-        expression: '1',
-        returnByValue: true,
-      })
-    } catch {
+    // Retry once here as well; reconnect races can briefly make an otherwise
+    // healthy tab look unavailable.
+    const valid = await validateAttachedTab(tabId)
+    if (!valid) {
       tabs.delete(tabId)
       if (tab.sessionId) tabBySession.delete(tab.sessionId)
       setBadge(tabId, 'off')
@@ -672,6 +705,11 @@ async function handleForwardCdpCommand(msg) {
     const toClose = target ? getTabByTargetId(target) : tabId
     if (!toClose) return { success: false }
     try {
+      const allTabs = await chrome.tabs.query({})
+      if (isLastRemainingTab(allTabs, toClose)) {
+        console.warn('Refusing to close the last tab: this would kill the browser process')
+        return { success: false, error: 'Cannot close the last tab' }
+      }
       await chrome.tabs.remove(toClose)
     } catch {
       return { success: false }