fix(ui): resolve collapsed header title overlap

lib/widgets/app_sliver_header.dart

@@ -44,7 +44,6 @@ class AppSliverHeader extends StatelessWidget {
     final colorScheme = Theme.of(context).colorScheme;
     final topPadding = normalizedHeaderTopPadding(context);
     final maxHeight = tokens.headerExpandedHeight + topPadding;
-    final minHeight = kToolbarHeight + topPadding;
     final edgeInset = detailHeaderEdgeInset(context);
 
     return SliverAppBar(
@@ -74,9 +73,21 @@ class AppSliverHeader extends StatelessWidget {
       actions: actions,
       flexibleSpace: LayoutBuilder(
         builder: (context, constraints) {
-          final expandRatio =
-              ((constraints.maxHeight - minHeight) / (maxHeight - minHeight))
-                  .clamp(0.0, 1.0);
+          // SliverAppBar adds the platform's actual top safe-area inset to its
+          // extents. Deriving the collapse ratio from our requested heights
+          // left notched iPhones looking almost fully expanded even after the
+          // toolbar had collapsed, so the large title occupied the back
+          // button's space. Read the resolved sliver geometry instead.
+          final settings = context
+              .dependOnInheritedWidgetOfExactType<FlexibleSpaceBarSettings>();
+          final minExtent = settings?.minExtent ?? kToolbarHeight;
+          final maxExtent = settings?.maxExtent ?? maxHeight;
+          final currentExtent =
+              settings?.currentExtent ?? constraints.maxHeight;
+          final extentDelta = maxExtent - minExtent;
+          final expandRatio = extentDelta > 0
+              ? ((currentExtent - minExtent) / extentDelta).clamp(0.0, 1.0)
+              : 0.0;
           final leftPadding = _showLeading
               ? (_leadingClearance + edgeInset) -
                     (((_leadingClearance + edgeInset) - _contentMargin) *

test/design_system_test.dart

@@ -341,6 +341,52 @@ void main() {
       expect(style.fontSize, AppTokens.standard.headerExpandedTitleSize);
     });
 
+    for (final platform in [TargetPlatform.iOS, TargetPlatform.android]) {
+      testWidgets(
+        'collapsed page title clears leading control on ${platform.name}',
+        (tester) async {
+          final controller = ScrollController();
+          addTearDown(controller.dispose);
+          final topInset = platform == TargetPlatform.iOS ? 59.0 : 24.0;
+
+          await tester.pumpWidget(
+            MaterialApp(
+              theme: AppTheme.light().copyWith(platform: platform),
+              home: MediaQuery(
+                data: MediaQueryData(
+                  size: const Size(430, 932),
+                  padding: EdgeInsets.only(top: topInset),
+                ),
+                child: Scaffold(
+                  body: CustomScrollView(
+                    controller: controller,
+                    slivers: const [
+                      AppSliverHeader.page(title: 'Metadata'),
+                      SliverToBoxAdapter(child: SizedBox(height: 1200)),
+                    ],
+                  ),
+                ),
+              ),
+            ),
+          );
+
+          controller.jumpTo(AppTokens.standard.headerExpandedHeight);
+          await tester.pump();
+
+          final title = find.text('Metadata');
+          final backIcon = find.byIcon(Icons.arrow_back);
+          expect(
+            tester.getRect(title).overlaps(tester.getRect(backIcon)),
+            isFalse,
+          );
+          expect(
+            tester.widget<Text>(title).style?.fontSize,
+            AppTokens.standard.headerCollapsedTitleSize,
+          );
+        },
+      );
+    }
+
     test('is the only collapsing header implementation left', () {
       final offenders = _libSources()
           .where(