diff --git a/dwds/debug_extension_mv3/web/background.dart b/dwds/debug_extension_mv3/web/background.dart
index 923e9d3a4..f18235745 100644
--- a/dwds/debug_extension_mv3/web/background.dart
+++ b/dwds/debug_extension_mv3/web/background.dart
@@ -89,6 +89,10 @@ void _handleRuntimeMessages(
           debugWarn('Received debug info but tab is missing.');
           return;
         }
+        // If this is a new Dart app, we need to clear old debug session data:
+        if (!await _matchesAppInStorage(debugInfo.appId, tabId: dartTab.id)) {
+          await clearStaleDebugSession(dartTab.id);
+        }
         // Save the debug info for the Dart app in storage:
         await setStorageObject<DebugInfo>(
             type: StorageObject.debugInfo, value: debugInfo, tabId: dartTab.id);
@@ -119,8 +123,9 @@ void _detectNavigationAwayFromDartApp(NavigationInfo navigationInfo) async {
   if (debugInfo == null) return;
   if (debugInfo.appUrl != navigationInfo.url) {
     _setDefaultIcon();
+    await clearStaleDebugSession(tabId);
     await removeStorageObject(type: StorageObject.debugInfo, tabId: tabId);
-    detachDebugger(
+    await detachDebugger(
       tabId,
       type: TabType.dartApp,
       reason: DetachReason.navigatedAwayFromApp,
@@ -153,3 +158,8 @@ Future<DebugInfo?> _fetchDebugInfo(int tabId) {
     tabId: tabId,
   );
 }
+
+Future<bool> _matchesAppInStorage(String? appId, {required int tabId}) async {
+  final debugInfo = await _fetchDebugInfo(tabId);
+  return appId != null && appId == debugInfo?.appId;
+}
diff --git a/dwds/debug_extension_mv3/web/debug_session.dart b/dwds/debug_extension_mv3/web/debug_session.dart
index 50e289384..29800cdbd 100644
--- a/dwds/debug_extension_mv3/web/debug_session.dart
+++ b/dwds/debug_extension_mv3/web/debug_session.dart
@@ -49,6 +49,7 @@ enum DetachReason {
   connectionDoneEvent,
   devToolsTabClosed,
   navigatedAwayFromApp,
+  staleDebugSession,
   unknown;
 
   factory DetachReason.fromString(String value) {
@@ -127,40 +128,60 @@ void attachDebugger(int dartAppTabId, {required Trigger trigger}) async {
   );
 }
 
-void detachDebugger(
+Future<bool> detachDebugger(
   int tabId, {
   required TabType type,
   required DetachReason reason,
 }) async {
   final debugSession = _debugSessionForTab(tabId, type: type);
-  if (debugSession == null) return;
+  if (debugSession == null) return false;
   final debuggee = Debuggee(tabId: debugSession.appTabId);
+  final completer = Completer<bool>();
   chrome.debugger.detach(debuggee, allowInterop(() {
     final error = chrome.runtime.lastError;
     if (error != null) {
       debugWarn(
           'Error detaching tab for reason: $reason. Error: ${error.message}');
+      completer.complete(false);
     } else {
       _handleDebuggerDetach(debuggee, reason);
+      completer.complete(true);
     }
   }));
+  return completer.future;
+}
+
+bool isActiveDebugSession(int tabId) =>
+    _debugSessionForTab(tabId, type: TabType.dartApp) != null;
+
+Future<void> clearStaleDebugSession(int tabId) async {
+  final debugSession = _debugSessionForTab(tabId, type: TabType.dartApp);
+  if (debugSession != null) {
+    await detachDebugger(
+      tabId,
+      type: TabType.dartApp,
+      reason: DetachReason.staleDebugSession,
+    );
+  } else {
+    await _removeDebugSessionDataInStorage(tabId);
+  }
 }
 
 void _registerDebugEventListeners() {
   chrome.debugger.onEvent.addListener(allowInterop(_onDebuggerEvent));
-  chrome.debugger.onDetach.addListener(allowInterop(
-    (source, _) => _handleDebuggerDetach(
+  chrome.debugger.onDetach.addListener(allowInterop((source, _) async {
+    await _handleDebuggerDetach(
       source,
       DetachReason.canceledByUser,
-    ),
-  ));
-  chrome.tabs.onRemoved.addListener(allowInterop(
-    (tabId, _) => detachDebugger(
+    );
+  }));
+  chrome.tabs.onRemoved.addListener(allowInterop((tabId, _) async {
+    await detachDebugger(
       tabId,
       type: TabType.devTools,
       reason: DetachReason.devToolsTabClosed,
-    ),
-  ));
+    );
+  }));
 }
 
 _enableExecutionContextReporting(int tabId) {
@@ -222,7 +243,7 @@ Future<void> _maybeConnectToDwds(int tabId, Object? params) async {
   );
   if (!connected) {
     debugWarn('Failed to connect to DWDS for $contextOrigin.');
-    _sendConnectFailureMessage(ConnectFailureReason.unknown,
+    await _sendConnectFailureMessage(ConnectFailureReason.unknown,
         dartAppTabId: tabId);
   }
 }
@@ -247,16 +268,16 @@ Future<bool> _connectToDwds({
     appTabId: dartAppTabId,
     trigger: trigger,
     onIncoming: (data) => _routeDwdsEvent(data, client, dartAppTabId),
-    onDone: () {
-      detachDebugger(
+    onDone: () async {
+      await detachDebugger(
         dartAppTabId,
         type: TabType.dartApp,
         reason: DetachReason.connectionDoneEvent,
       );
     },
-    onError: (err) {
+    onError: (err) async {
       debugWarn('Connection error: $err', verbose: true);
-      detachDebugger(
+      await detachDebugger(
         dartAppTabId,
         type: TabType.dartApp,
         reason: DetachReason.connectionErrorEvent,
@@ -377,7 +398,7 @@ void _openDevTools(String devToolsUri, {required int dartAppTabId}) async {
   }
 }
 
-void _handleDebuggerDetach(Debuggee source, DetachReason reason) async {
+Future<void> _handleDebuggerDetach(Debuggee source, DetachReason reason) async {
   final tabId = source.tabId;
   debugLog(
     'Debugger detached due to: $reason',
@@ -385,16 +406,18 @@ void _handleDebuggerDetach(Debuggee source, DetachReason reason) async {
     prefix: '$tabId',
   );
   final debugSession = _debugSessionForTab(tabId, type: TabType.dartApp);
-  if (debugSession == null) return;
-  debugLog('Removing debug session...');
-  _removeDebugSession(debugSession);
-  // Notify the extension panels that the debug session has ended:
-  _sendStopDebuggingMessage(reason, dartAppTabId: source.tabId);
-  // Remove the DevTools URI and encoded URI from storage:
-  await removeStorageObject(type: StorageObject.devToolsUri, tabId: tabId);
-  await removeStorageObject(type: StorageObject.encodedUri, tabId: tabId);
-  // Maybe close the associated DevTools tab as well:
-  final devToolsTabId = debugSession.devToolsTabId;
+  if (debugSession != null) {
+    debugLog('Removing debug session...');
+    _removeDebugSession(debugSession);
+    // Notify the extension panels that the debug session has ended:
+    await _sendStopDebuggingMessage(reason, dartAppTabId: tabId);
+    // Maybe close the associated DevTools tab as well:
+    await _maybeCloseDevTools(debugSession.devToolsTabId);
+  }
+  await _removeDebugSessionDataInStorage(tabId);
+}
+
+Future<void> _maybeCloseDevTools(int? devToolsTabId) async {
   if (devToolsTabId == null) return;
   final devToolsTab = await getTab(devToolsTabId);
   if (devToolsTab != null) {
@@ -403,6 +426,12 @@ void _handleDebuggerDetach(Debuggee source, DetachReason reason) async {
   }
 }
 
+Future<void> _removeDebugSessionDataInStorage(int tabId) async {
+  // Remove the DevTools URI and encoded URI from storage:
+  await removeStorageObject(type: StorageObject.devToolsUri, tabId: tabId);
+  await removeStorageObject(type: StorageObject.encodedUri, tabId: tabId);
+}
+
 void _removeDebugSession(_DebugSession debugSession) {
   // Note: package:sse will try to keep the connection alive, even after the
   // client has been closed. Therefore the extension sends an event to notify
@@ -422,25 +451,25 @@ void _removeDebugSession(_DebugSession debugSession) {
   }
 }
 
-void _sendConnectFailureMessage(ConnectFailureReason reason,
+Future<bool> _sendConnectFailureMessage(ConnectFailureReason reason,
     {required int dartAppTabId}) async {
   final json = jsonEncode(serializers.serialize(ConnectFailure((b) => b
     ..tabId = dartAppTabId
     ..reason = reason.name)));
-  sendRuntimeMessage(
+  return await sendRuntimeMessage(
       type: MessageType.connectFailure,
       body: json,
       sender: Script.background,
       recipient: Script.debuggerPanel);
 }
 
-void _sendStopDebuggingMessage(DetachReason reason,
+Future<bool> _sendStopDebuggingMessage(DetachReason reason,
     {required int dartAppTabId}) async {
   final json = jsonEncode(serializers.serialize(DebugStateChange((b) => b
     ..tabId = dartAppTabId
     ..reason = reason.name
     ..newState = DebugStateChange.stopDebugging)));
-  sendRuntimeMessage(
+  return await sendRuntimeMessage(
       type: MessageType.debugStateChange,
       body: json,
       sender: Script.background,
@@ -478,7 +507,7 @@ Future<bool> _authenticateUser(int tabId) async {
       tabId: tabId,
     );
   } else {
-    _sendConnectFailureMessage(
+    await _sendConnectFailureMessage(
       ConnectFailureReason.authentication,
       dartAppTabId: tabId,
     );
@@ -622,8 +651,20 @@ class _DebugSession {
   }
 
   void close() {
-    _socketClient.close();
-    _batchSubscription.cancel();
-    _batchController.close();
+    try {
+      _socketClient.close();
+    } catch (error) {
+      debugError('Error closing socket client: $error');
+    }
+    try {
+      _batchSubscription.cancel();
+    } catch (error) {
+      debugError('Error canceling batch subscription: $error');
+    }
+    try {
+      _batchController.close();
+    } catch (error) {
+      debugError('Error closing batch controller: $error');
+    }
   }
 }
diff --git a/dwds/debug_extension_mv3/web/detector.dart b/dwds/debug_extension_mv3/web/detector.dart
index 74c8aa055..ec75374c1 100644
--- a/dwds/debug_extension_mv3/web/detector.dart
+++ b/dwds/debug_extension_mv3/web/detector.dart
@@ -26,14 +26,14 @@ void _registerListeners() {
   document.addEventListener('dart-auth-response', _onDartAuthEvent);
 }
 
-void _onDartAppReadyEvent(Event event) {
+Future<void> _onDartAppReadyEvent(Event event) async {
   final debugInfo = getProperty(event, 'detail') as String?;
   if (debugInfo == null) {
     debugWarn(
         'No debug info sent with ready event, instead reading from Window.');
     _injectDebugInfoScript();
   } else {
-    _sendMessageToBackgroundScript(
+    await _sendMessageToBackgroundScript(
       type: MessageType.debugInfo,
       body: debugInfo,
     );
@@ -41,10 +41,10 @@ void _onDartAppReadyEvent(Event event) {
   }
 }
 
-void _onDartAuthEvent(Event event) {
+Future<void> _onDartAuthEvent(Event event) async {
   final isAuthenticated = getProperty(event, 'detail') as String?;
   if (isAuthenticated == null) return;
-  _sendMessageToBackgroundScript(
+  await _sendMessageToBackgroundScript(
     type: MessageType.isAuthenticated,
     body: isAuthenticated,
   );
@@ -61,11 +61,11 @@ void _injectDebugInfoScript() {
   document.head?.append(script);
 }
 
-void _sendMessageToBackgroundScript({
+Future<void> _sendMessageToBackgroundScript({
   required MessageType type,
   required String body,
-}) {
-  sendRuntimeMessage(
+}) async {
+  await sendRuntimeMessage(
     type: type,
     body: body,
     sender: Script.detector,
diff --git a/dwds/debug_extension_mv3/web/messaging.dart b/dwds/debug_extension_mv3/web/messaging.dart
index a40d755fc..c7345fe26 100644
--- a/dwds/debug_extension_mv3/web/messaging.dart
+++ b/dwds/debug_extension_mv3/web/messaging.dart
@@ -5,6 +5,7 @@
 @JS()
 library messaging;
 
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:js/js.dart';
@@ -100,7 +101,7 @@ void interceptMessage<T>({
   }
 }
 
-void sendRuntimeMessage(
+Future<bool> sendRuntimeMessage(
     {required MessageType type,
     required String body,
     required Script sender,
@@ -111,10 +112,19 @@ void sendRuntimeMessage(
     type: type,
     body: body,
   );
+  final completer = Completer<bool>();
   chrome.runtime.sendMessage(
     /*id*/ null,
     message.toJSON(),
     /*options*/ null,
-    /*callback*/ null,
+    allowInterop(() {
+      final error = chrome.runtime.lastError;
+      if (error != null) {
+        debugError(
+            'Error sending $type to $recipient from $sender: ${error.message}');
+      }
+      completer.complete(error != null);
+    }),
   );
+  return completer.future;
 }
diff --git a/dwds/debug_extension_mv3/web/panel.dart b/dwds/debug_extension_mv3/web/panel.dart
index f04d0b726..f5a44e4e2 100644
--- a/dwds/debug_extension_mv3/web/panel.dart
+++ b/dwds/debug_extension_mv3/web/panel.dart
@@ -5,6 +5,7 @@
 @JS()
 library panel;
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:html';
 
@@ -40,22 +41,32 @@ const _showClass = 'show';
 const _warningBannerId = 'warningBanner';
 const _warningMsgId = 'warningMsg';
 
+const _noAppDetectedMsg = 'No app detected.';
+const _lostConnectionMsg = 'Lost connection.';
+const _connectionTimeoutMsg = 'Connection timed out.';
+const _failedToConnectMsg = 'Failed to connect, please try again.';
+const _pleaseAuthenticateMsg = 'Please re-authenticate and try again.';
+
 int get _tabId => chrome.devtools.inspectedWindow.tabId;
 
 void main() {
-  _registerListeners();
+  unawaited(
+    _registerListeners().catchError((error) {
+      debugWarn('Error registering listeners in panel: $error');
+    }),
+  );
   _setColorThemeToMatchChromeDevTools();
   _maybeUpdateFileABugLink();
 }
 
-void _registerListeners() {
+Future<void> _registerListeners() async {
   chrome.storage.onChanged.addListener(allowInterop(_handleStorageChanges));
   chrome.runtime.onMessage.addListener(allowInterop(_handleRuntimeMessages));
   final launchDebugConnectionButton =
       document.getElementById(_launchDebugConnectionButtonId) as ButtonElement;
   launchDebugConnectionButton.addEventListener('click', _launchDebugConnection);
 
-  _maybeInjectDevToolsIframe();
+  await _maybeInjectDevToolsIframe();
 }
 
 void _handleRuntimeMessages(
@@ -114,11 +125,15 @@ void _handleStorageChanges(Object storageObj, String storageArea) {
 void _handleDebugInfoChanges(DebugInfo? debugInfo) async {
   if (debugInfo == null && _isDartApp) {
     _isDartApp = false;
-    _showWarningBanner('Dart app is no longer open.');
+    if (!_warningBannerIsVisible()) {
+      _showWarningBanner(_noAppDetectedMsg);
+    }
   }
   if (debugInfo != null && !_isDartApp) {
     _isDartApp = true;
-    _hideWarningBanner();
+    if (_warningBannerIsVisible()) {
+      _hideWarningBanner();
+    }
   }
 }
 
@@ -171,33 +186,45 @@ void _handleDebugConnectionLost(String? reason) {
   final detachReason = DetachReason.fromString(reason ?? 'unknown');
   _removeDevToolsIframe();
   _updateElementVisibility(_landingPageId, visible: true);
-  if (detachReason != DetachReason.canceledByUser) {
-    _showWarningBanner('Lost connection.');
+  switch (detachReason) {
+    case DetachReason.canceledByUser:
+      return;
+    case DetachReason.staleDebugSession:
+    case DetachReason.navigatedAwayFromApp:
+      _showWarningBanner(_noAppDetectedMsg);
+      break;
+    default:
+      _showWarningBanner(_lostConnectionMsg);
+      break;
   }
 }
 
 void _handleConnectFailure(ConnectFailureReason reason) {
   switch (reason) {
     case ConnectFailureReason.authentication:
-      _showWarningBanner('Please re-authenticate and try again.');
+      _showWarningBanner(_pleaseAuthenticateMsg);
       break;
     case ConnectFailureReason.noDartApp:
-      _showWarningBanner('No Dart app detected.');
+      _showWarningBanner(_noAppDetectedMsg);
       break;
     case ConnectFailureReason.timeout:
-      _showWarningBanner('Connection timed out.');
+      _showWarningBanner(_connectionTimeoutMsg);
       break;
     default:
-      _showWarningBanner('Failed to connect, please try again.');
+      _showWarningBanner(_failedToConnectMsg);
   }
   _updateElementVisibility(_launchDebugConnectionButtonId, visible: true);
   _updateElementVisibility(_loadingSpinnerId, visible: false);
 }
 
+bool _warningBannerIsVisible() {
+  final warningBanner = document.getElementById(_warningBannerId);
+  return warningBanner != null && warningBanner.classes.contains(_showClass);
+}
+
 void _showWarningBanner(String message) {
   final warningMsg = document.getElementById(_warningMsgId);
   warningMsg?.setInnerHtml(message);
-  print(warningMsg);
   final warningBanner = document.getElementById(_warningBannerId);
   warningBanner?.classes.add(_showClass);
 }
@@ -213,7 +240,7 @@ void _launchDebugConnection(Event _) async {
   final json = jsonEncode(serializers.serialize(DebugStateChange((b) => b
     ..tabId = _tabId
     ..newState = DebugStateChange.startDebugging)));
-  sendRuntimeMessage(
+  await sendRuntimeMessage(
       type: MessageType.debugStateChange,
       body: json,
       sender: Script.debuggerPanel,
@@ -229,10 +256,15 @@ void _maybeHandleConnectionTimeout() async {
   }
 }
 
-void _maybeInjectDevToolsIframe() async {
+Future<void> _maybeInjectDevToolsIframe() async {
   final devToolsUri = await fetchStorageObject<String>(
       type: StorageObject.devToolsUri, tabId: _tabId);
-  if (devToolsUri != null) {
+  if (devToolsUri == null) return;
+  if (isActiveDebugSession(_tabId)) {
+    debugWarn('Unexpected state. Stale DevTools URI.');
+    await clearStaleDebugSession(_tabId);
+    _updateElementVisibility(_landingPageId, visible: true);
+  } else {
     _injectDevToolsIframe(devToolsUri);
   }
 }
@@ -250,7 +282,7 @@ void _injectDevToolsIframe(String devToolsUri) {
       'ide': 'ChromeDevTools',
       'embed': 'true',
       'page': panelType,
-      '_backgroundColor': _backgroundColor,
+      'backgroundColor': _backgroundColor,
     },
   );
   iframe.setAttribute('src', iframeSrc);
diff --git a/dwds/test/puppeteer/extension_test.dart b/dwds/test/puppeteer/extension_test.dart
index 2c8e08c68..8731dfce5 100644
--- a/dwds/test/puppeteer/extension_test.dart
+++ b/dwds/test/puppeteer/extension_test.dart
@@ -608,7 +608,7 @@ void main() async {
               // Expect the Dart DevTools IFRAME to be added:
               final devToolsUrlFragment =
                   'ide=ChromeDevTools&embed=true&page=debugger';
-              final iframeTarget = await browser.waitForTarget(
+              var iframeTarget = await browser.waitForTarget(
                 (target) => target.url.contains(devToolsUrlFragment),
               );
               var iframeDestroyed = false;
@@ -635,8 +635,25 @@ void main() async {
                 screenshotName:
                     'debuggerPanelDisconnected_${isFlutterApp ? 'flutterApp' : 'dartApp'}',
               );
+              // Navigate back to the Dart app:
+              await appTab.goto(context.appUrl, wait: Until.domContentLoaded);
+              // Click the launch button again
+              await _clickLaunchButton(
+                browser,
+                panel: Panel.debugger,
+              );
+              // Expect the Dart DevTools IFRAME to be added again:
+              iframeTarget = await browser.waitForTarget(
+                (target) => target.url.contains(devToolsUrlFragment),
+              );
+              expect(iframeTarget, isNotNull);
             });
 
+            // TODO(elliette): Pull TestServer out of TestContext, so we can add
+            // a test case for starting another test app, loading that app in
+            // the tab we were debugging, and be able to reconnect to that one.
+            // See https://github.com/dart-lang/webdev/issues/1779
+
             test('The Dart DevTools IFRAME has the correct query parameters',
                 () async {
               final chromeDevToolsPage = await getChromeDevToolsPage(browser);
diff --git a/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_dartApp.png b/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_dartApp.png
index 1e0ad8b7a..96ac4caa6 100644
Binary files a/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_dartApp.png and b/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_dartApp.png differ
diff --git a/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_flutterApp.png b/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_flutterApp.png
index 1e0ad8b7a..c8040bfe3 100644
Binary files a/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_flutterApp.png and b/dwds/test/puppeteer/test_images/debuggerPanelDisconnected_flutterApp.png differ