fix: address texture watchdog/probe review findings

- watchdog: compare the plugin's cumulative consumed counter against a
  snapshot taken when arming (re-arm was a no-op before), and judge on
  cumulative pushes + elapsed time so sparse damage-driven streams are
  still detected
- failure handling is idempotent (one record per breakage) and updates
  every render session like main_set_local_option does, not only the
  failing one; the fallback toast is not claimed for multi-display
  windows the soft path cannot rescue
- probe: skip when the consumed API is missing (old plugin) or a
  raster-stall is recorded (compositing could hang the main window);
  a fail verdict requires fresh frame timings and a non-minimized
  window; a pass never clears failed-raster-stall; toast only when
  texture rendering was effectively on; probe pixel is transparent
- raster-stall monitor: judge on frame-timing staleness (a mid-episode
  hang was undetectable before), gate on lifecycle/minimized/idle with
  a moving quiet anchor, threshold 30s, shared with the camera page;
  clear stateGlobal minimized flag on plain window restore
- adopt mismatched frame sizes only in multi-ui-session mode (legacy
  mode pairs frames loosely and could ping-pong between displays)
- drop the now-dead closeSession parameter from texture destroy();
  trim comments to repo style

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

flutter/lib/desktop/widgets/raster_stall_monitor.dart

@@ -0,0 +1,52 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
+
+import '../../common.dart';
+import '../../consts.dart';
+import '../../models/platform_model.dart';
+import '../../models/state_model.dart';
+
+/// Records a hung raster thread (frames continuously scheduled but no frame
+/// timings delivered for 30s) in `texture-render-health`; a hang cannot be
+/// rescued in-process, so the next launch defaults texture rendering off.
+class RasterStallMonitor {
+  static bool _started = false;
+  static bool _reported = false;
+  static DateTime? _lastTimings;
+  static DateTime _lastQuiet = DateTime.now();
+
+  static void start() {
+    if (_started || isWeb) return;
+    _started = true;
+    SchedulerBinding.instance.addTimingsCallback((_) {
+      _lastTimings = DateTime.now();
+    });
+    Timer.periodic(const Duration(seconds: 2), (_) {
+      if (_reported) return;
+      final now = DateTime.now();
+      final lifecycle = SchedulerBinding.instance.lifecycleState;
+      // Minimized/inactive (incl. screen lock) or idle (nothing scheduled):
+      // no timings is legitimate, keep moving the quiet anchor forward.
+      if (stateGlobal.isMinimized ||
+          (lifecycle != null && lifecycle != AppLifecycleState.resumed) ||
+          !SchedulerBinding.instance.hasScheduledFrame) {
+        _lastQuiet = now;
+        return;
+      }
+      var ref = _lastQuiet;
+      final lastTimings = _lastTimings;
+      if (lastTimings != null && lastTimings.isAfter(ref)) {
+        ref = lastTimings;
+      }
+      if (now.difference(ref) > const Duration(seconds: 30)) {
+        _reported = true;
+        bind.mainSetLocalOption(
+            key: kOptionTextureRenderHealth, value: 'failed-raster-stall');
+        debugPrint(
+            'raster thread stall detected, texture rendering disabled for next launch');
+      }
+    });
+  }
+}