multiple runtime bugfixes for 1.5.5+65

lib/widget/route_transition_gate.dart

@@ -14,6 +14,15 @@ import 'app_progress_indicator.dart';
 /// subtree for [placeholder] for the duration of any transition; the status
 /// listener fires before that frame's layout, so the fragile subtree is gone
 /// before the new transform lays out.
+///
+/// On top of that the gate always yields one idle post-frame (`_settled`)
+/// before mounting [builder], whether or not a route animation ran. A
+/// `RenderTransform` is a `RenderProxyBox` and only takes its size *after*
+/// laying out its child, so during that first pass `size` throws — and route
+/// transitions are not the only source of a fresh transform: `PersistentTabView`
+/// wraps every tab screen in an animated `Transform.translate` and builds a tab
+/// lazily on first activation, which is how the ticker's in-place PDF pages hit
+/// the same window with no route animation in sight.
 class RouteTransitionGate extends StatefulWidget {
   const RouteTransitionGate({super.key, required this.builder, this.placeholder});
 
@@ -31,6 +40,11 @@ class _RouteTransitionGateState extends State<RouteTransitionGate> {
   Animation<double>? _animation;
   Animation<double>? _secondaryAnimation;
 
+  /// Becomes true one idle post-frame after the last transition ended; only
+  /// then is [RouteTransitionGate.builder] safe to mount (see class doc).
+  bool _settled = false;
+  bool _settleScheduled = false;
+
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
@@ -68,15 +82,32 @@ class _RouteTransitionGateState extends State<RouteTransitionGate> {
       status == AnimationStatus.forward || status == AnimationStatus.reverse;
 
   void _onAnimationStatus(AnimationStatus status) {
-    if (mounted) setState(() {});
+    if (!mounted) return;
+    // A (re)starting transition invalidates the settled state; it has to be
+    // re-earned once the transition finishes.
+    setState(() {
+      if (_transitioning) _settled = false;
+    });
+  }
+
+  void _scheduleSettle() {
+    if (_settleScheduled) return;
+    _settleScheduled = true;
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      _settleScheduled = false;
+      if (mounted && !_transitioning && !_settled) {
+        setState(() => _settled = true);
+      }
+    });
   }
 
   @override
   Widget build(BuildContext context) {
-    if (_transitioning) {
-      return widget.placeholder ??
-          const Center(child: AppProgressIndicator.large());
+    if (!_transitioning) {
+      if (_settled) return widget.builder(context);
+      _scheduleSettle();
     }
-    return widget.builder(context);
+    return widget.placeholder ??
+        const Center(child: AppProgressIndicator.large());
   }
 }