diff --git a/docs/reports/2026-04-08-acp-http-404-repro-verification.md b/docs/reports/2026-04-08-acp-http-404-repro-verification.md
new file mode 100644
index 00000000..5d0be061
--- /dev/null
+++ b/docs/reports/2026-04-08-acp-http-404-repro-verification.md
@@ -0,0 +1,55 @@
+# ACP HTTP 404 场景自动复现验证
+
+## 变更摘要
+
+本次验证目标不是再次修复，而是确认 `ACP_HTTP_404: ACP HTTP request failed (404) · unexpected content type: text/plain` 这一类场景能否通过自动化测试稳定复现，并作为后续回归证据保留。
+
+验证对象聚焦在 ACP runtime transport 行为：
+
+- 当客户端以 `http(s)` 基址优先请求 `/acp/rpc`
+- 服务端返回 `404`
+- 且 `content-type` 为 `text/plain`
+- 但同一基址下 `/acp` WebSocket 仍可正常响应
+
+该场景现在由 `test/runtime/gateway_acp_client_suite.dart` 内的专门用例覆盖。
+
+## 测试命令与结果
+
+- `flutter test test/runtime/gateway_acp_client_test.dart --reporter expanded --plain-name "falls back to websocket when HTTP bridge returns plain-text 404"`
+  - 结果：通过
+  - 关键输出：`GatewayAcpClient falls back to websocket when HTTP bridge returns plain-text 404`
+- `flutter test test/runtime/gateway_acp_client_test.dart --reporter expanded`
+  - 结果：通过
+  - 关键输出：`00:00 +12: All tests passed!`
+- `flutter analyze`
+  - 结果：通过
+  - 关键输出：`No issues found!`
+
+## 重点验证点覆盖
+
+- 已验证：自动化测试可以稳定构造“`/acp/rpc` 返回 `404 text/plain`，但 `/acp` WebSocket 可用”的复现场景。
+- 已验证：当前实现会在该场景下从 HTTP bridge 失败回退到 WebSocket，并成功获取 ACP capabilities。
+- 已验证：原有错误分类仍保留，`text/html` 这类网页响应不会被误判为可回退场景。
+- 已验证：相关 ACP client suite 全量回归通过，没有引入同文件内的其他协议回归。
+
+## 失败项
+
+- 无自动化失败项。
+
+## 高风险回归点
+
+- ACP transport 是运行时核心链路，涉及 HTTP / WebSocket 双通道切换，属于中高风险协议行为。
+- 当前自动化复现基于 fake server，覆盖的是协议级场景，不等同于已经对用户机器上的真实 `127.0.0.1:18789` 服务完成实机重放。
+
+## 建议人工补测项
+
+- 如果需要证明“截图里的真实本地服务”与自动化场景完全一致，建议对用户当前本地 gateway 做一次实机补测：
+  - 在真实 `127.0.0.1:18789` 上确认 `/acp/rpc` 是否返回 `404 text/plain`
+  - 同时确认 `/acp` WebSocket 是否可握手并返回 `acp.capabilities`
+  - 从 Desktop UI 发起一次与截图相同的对话请求，确认不再出现该报错
+
+## 相关文件
+
+- `test/runtime/gateway_acp_client_suite.dart`
+- `test/runtime/gateway_acp_client_test.dart`
+- `lib/runtime/gateway_acp_client.dart`
diff --git a/integration_test/desktop_navigation_flow_test.dart b/integration_test/desktop_navigation_flow_test.dart
index f76a7781..085f43a9 100644
--- a/integration_test/desktop_navigation_flow_test.dart
+++ b/integration_test/desktop_navigation_flow_test.dart
@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../test/helpers/test_keys.dart';
 import 'test_support.dart';
 
 Finder _textEither(String zh, String en) {
@@ -45,6 +46,7 @@ void main() {
     WidgetTester tester,
   ) async {
     await pumpDesktopApp(tester);
+    await waitForIntegrationFinder(tester, find.byKey(TestKeys.assistantTaskRail));
 
     expect(_textEither('新对话', 'New conversation'), findsWidgets);
     await tester.tap(
diff --git a/integration_test/desktop_settings_flow_test.dart b/integration_test/desktop_settings_flow_test.dart
index 8f9772c1..8ba5168b 100644
--- a/integration_test/desktop_settings_flow_test.dart
+++ b/integration_test/desktop_settings_flow_test.dart
@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../test/helpers/test_keys.dart';
 import 'test_support.dart';
 
 Finder _textEither(String zh, String en) {
@@ -45,6 +46,7 @@ void main() {
     'desktop shell exposes settings entry for gateway configuration',
     (WidgetTester tester) async {
       await pumpDesktopApp(tester);
+      await waitForIntegrationFinder(tester, find.byKey(TestKeys.assistantTaskRail));
 
       await tester.tap(
         find.byKey(const Key('assistant-side-pane-tab-navigation')),
diff --git a/test/features/assistant_page_single_agent_flow_suite.dart b/test/features/assistant_page_single_agent_flow_suite.dart
index 2051702b..cdcb96e9 100644
--- a/test/features/assistant_page_single_agent_flow_suite.dart
+++ b/test/features/assistant_page_single_agent_flow_suite.dart
@@ -10,6 +10,20 @@ import 'package:xworkmate/runtime/runtime_models.dart';
 
 import '../test_support.dart';
 
+Future<void> _waitForText(
+  WidgetTester tester,
+  Finder finder, {
+  Duration timeout = const Duration(seconds: 10),
+}) async {
+  final deadline = DateTime.now().add(timeout);
+  while (finder.evaluate().isEmpty) {
+    if (DateTime.now().isAfter(deadline)) {
+      fail('Timed out waiting for ${finder.description}');
+    }
+    await tester.pump(const Duration(milliseconds: 50));
+  }
+}
+
 void main() {
   testWidgets(
     'AssistantPage single agent can be selected and receive streaming reply',
@@ -57,7 +71,7 @@ void main() {
       );
       await tester.pump();
       await tester.pump(const Duration(milliseconds: 200));
-      await tester.pumpAndSettle();
+      await _waitForText(tester, find.textContaining('CODEX_REPLY'));
 
       expect(find.textContaining('CODEX_REPLY'), findsWidgets);
       expect(server.requestCount, greaterThanOrEqualTo(1));
@@ -108,7 +122,9 @@ class _ChatServer {
         HttpHeaders.contentTypeHeader,
         'text/event-stream; charset=utf-8',
       );
+      request.response.headers.set(HttpHeaders.cacheControlHeader, 'no-cache');
       request.response.write('data: ${jsonEncode(response)}\n\n');
+      await request.response.flush();
       await request.response.close();
     }
   }
diff --git a/test/features/settings_page_external_acp_end_to_end_suite.dart b/test/features/settings_page_external_acp_end_to_end_suite.dart
index f409daa1..59698ed1 100644
--- a/test/features/settings_page_external_acp_end_to_end_suite.dart
+++ b/test/features/settings_page_external_acp_end_to_end_suite.dart
@@ -11,6 +11,20 @@ import 'package:xworkmate/runtime/runtime_models_profiles.dart';
 
 import '../test_support.dart';
 
+Future<void> _waitForText(
+  WidgetTester tester,
+  Finder finder, {
+  Duration timeout = const Duration(seconds: 10),
+}) async {
+  final deadline = DateTime.now().add(timeout);
+  while (finder.evaluate().isEmpty) {
+    if (DateTime.now().isAfter(deadline)) {
+      fail('Timed out waiting for ${finder.description}');
+    }
+    await tester.pump(const Duration(milliseconds: 50));
+  }
+}
+
 void main() {
   testWidgets('SettingsPage Codex external ACP can test and save', (
     WidgetTester tester,
@@ -47,20 +61,21 @@ void main() {
       const ValueKey<String>('external-acp-test-Codex'),
     );
     final saveButton = find.byKey(
-      const ValueKey<String>('external-acp-apply-Codex'),
+      const ValueKey<String>('external-acp-save-Codex'),
     );
 
     expect(endpointField, findsOneWidget);
     await tester.enterText(endpointField, server.baseUri.toString());
-    await tester.pumpAndSettle();
+    await tester.pump();
 
     await tester.tap(testButton);
-    await tester.pumpAndSettle();
+    await tester.pump(const Duration(milliseconds: 100));
+    await _waitForText(tester, find.textContaining('连接成功'));
 
     expect(find.textContaining('连接成功'), findsOneWidget);
 
     await tester.tap(saveButton);
-    await tester.pumpAndSettle();
+    await tester.pump();
 
     final saved = controller.settings.externalAcpEndpointForProviderId('codex');
     expect(saved?.endpoint, server.baseUri.toString());
@@ -110,7 +125,9 @@ class _AcpServer {
         HttpHeaders.contentTypeHeader,
         'text/event-stream; charset=utf-8',
       );
+      request.response.headers.set(HttpHeaders.cacheControlHeader, 'no-cache');
       request.response.write('data: ${jsonEncode(response)}\n\n');
+      await request.response.flush();
       await request.response.close();
     }
   }
diff --git a/test/features/settings_page_suite.dart b/test/features/settings_page_suite.dart
index a0852607..8f947e91 100644
--- a/test/features/settings_page_suite.dart
+++ b/test/features/settings_page_suite.dart
@@ -673,7 +673,7 @@ paths:
       ValueKey('external-acp-test-${customProfile.providerKey}'),
     );
     final applyButton = find.byKey(
-      ValueKey('external-acp-apply-${customProfile.providerKey}'),
+      ValueKey('external-acp-save-${customProfile.providerKey}'),
     );
 
     expect(labelField, findsOneWidget);