fix: address codex review findings on probe/watchdog fallback

- a probe or raster-stall failure record now also downgrades sessions
  that are already running: main_set_local_option broadcasts the
  fallback for failed-* health writes, which also closes the hole where
  the watchdog's idempotence guard no-oped after the probe had already
  written the record
- probe success requires a frame timing newer than the first push:
  'consumed' advances inside the plugin callback before the GL/Metal
  upload, so a raster thread hanging in the driver no longer counts as
  a pass (and cannot clear a previous failure)
- watchdog failures are tagged with the failing backend
  (failed-watchdog-rgba/gpu); the rgba-only probe clears only the rgba
  class, so a working pixel-buffer path can no longer re-enable a
  broken D3D shared-handle path every launch
- the watchdog pauses while the session's window is hidden (new
  session_set_render_visible FFI wired to the window minimize/restore
  events): a display registered in a minimized window no longer records
  a false global failure; observation now counts pushes within the
  window rather than since registration
- probe failure verdicts additionally require a resumed lifecycle,
  matching the raster-stall monitor
- linux plugin: deferred-unref grace lengthened to 10s (no raster-side
  completion barrier exists; documented as heuristic), ref bumped

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

flutter/lib/desktop/widgets/tabbar_widget.dart

@@ -11,6 +11,7 @@ import 'package:flutter_hbb/consts.dart';
 import 'package:flutter_hbb/desktop/pages/remote_page.dart';
 import 'package:flutter_hbb/desktop/pages/view_camera_page.dart';
 import 'package:flutter_hbb/main.dart';
+import 'package:flutter_hbb/models/model.dart';
 import 'package:flutter_hbb/models/platform_model.dart';
 import 'package:flutter_hbb/models/state_model.dart';
 import 'package:get/get.dart';
@@ -388,6 +389,7 @@ class _DesktopTabState extends State<DesktopTab>
   void onWindowMinimize() {
     stateGlobal.setMinimized(true);
     stateGlobal.setMaximized(false);
+    _updateSessionsRenderVisible(false);
     super.onWindowMinimize();
   }
 
@@ -395,6 +397,7 @@ class _DesktopTabState extends State<DesktopTab>
   void onWindowMaximize() {
     stateGlobal.setMinimized(false);
     _setMaximized(true);
+    _updateSessionsRenderVisible(true);
     super.onWindowMaximize();
   }
 
@@ -402,6 +405,7 @@ class _DesktopTabState extends State<DesktopTab>
   void onWindowUnmaximize() {
     stateGlobal.setMinimized(false);
     _setMaximized(false);
+    _updateSessionsRenderVisible(true);
     super.onWindowUnmaximize();
   }
 
@@ -409,9 +413,26 @@ class _DesktopTabState extends State<DesktopTab>
   void onWindowRestore() {
     // A plain restore (no maximize involved) must clear the minimized flag.
     stateGlobal.setMinimized(false);
+    _updateSessionsRenderVisible(true);
     super.onWindowRestore();
   }
 
+  // A hidden window composites nothing; pause the Rust-side texture watchdog
+  // for its sessions so it cannot record a false failure.
+  void _updateSessionsRenderVisible(bool visible) {
+    if (tabType != DesktopTabType.remoteScreen &&
+        tabType != DesktopTabType.viewCamera) {
+      return;
+    }
+    for (final tab in controller.state.value.tabs) {
+      try {
+        final ffi = Get.find<FFI>(tag: tab.key);
+        bind.sessionSetRenderVisible(
+            sessionId: ffi.sessionId, visible: visible);
+      } catch (_) {}
+    }
+  }
+
   _saveFrame({bool? flush}) async {
     try {
       if (tabType == DesktopTabType.main) {