diff --git a/lib/theme/theme.dart b/lib/theme/theme.dart
index 55dad2e..e593618 100644
--- a/lib/theme/theme.dart
+++ b/lib/theme/theme.dart
@@ -26,12 +26,24 @@
 // [Palette] (not the live getters) so the light + dark ThemeData objects are
 // each internally consistent regardless of which mode is currently active.
 
-// CupertinoPageTransitionsBuilder (used below for iOS/macOS) comes from
-// material.dart on the pinned toolchain (Flutter 3.41.6 — see
-// .github/workflows/test.yml). It moved between cupertino.dart and
-// material.dart across Flutter versions, so if you bump the pin and this
-// suddenly fails to resolve, re-add:
-//   import 'package:flutter/cupertino.dart' show CupertinoPageTransitionsBuilder;
+// iOS/macOS page transitions are NOT named here on purpose.
+//
+// CupertinoPageTransitionsBuilder has MOVED between SDK versions: on 3.41.6
+// (the pinned toolchain, see .github/workflows/test.yml) material.dart exports
+// it and cupertino.dart does not; on 3.44.x it is the other way round. So there
+// is no single import that compiles on both — importing from cupertino breaks
+// the pin with "doesn't export a member with the shown name", and importing
+// from material breaks newer SDKs with "isn't defined", which also takes the
+// surrounding const map down with it.
+//
+// Spreading PageTransitionsTheme's own defaults sidesteps the question: the SDK
+// already maps iOS/macOS to whatever Cupertino builder that version ships, so
+// we override only the platforms we actually want changed and never name the
+// moving class. Version-proof in both directions.
+//
+// Do not "simplify" this back to an explicit iOS entry. The Cupertino builder
+// is what supplies the interactive edge-swipe-back gesture — see
+// page_transitions.dart's navigation contract.
 import 'package:flutter/material.dart';
 import 'page_transitions.dart';
 import 'tokens.dart';
@@ -205,14 +217,14 @@ ThemeData buildOpenStrapTheme(Palette p) {
     // routes stay MaterialPageRoutes: iOS keeps the native slide transition
     // AND the interactive edge-swipe-back gesture; Android-likes get the
     // app's shared-axis fade-through. See page_transitions.dart.
-    pageTransitionsTheme: const PageTransitionsTheme(
+    pageTransitionsTheme: PageTransitionsTheme(
       builders: {
-        TargetPlatform.android: SharedAxisPageTransitionsBuilder(),
-        TargetPlatform.fuchsia: SharedAxisPageTransitionsBuilder(),
-        TargetPlatform.linux: SharedAxisPageTransitionsBuilder(),
-        TargetPlatform.windows: SharedAxisPageTransitionsBuilder(),
-        TargetPlatform.iOS: CupertinoPageTransitionsBuilder(),
-        TargetPlatform.macOS: CupertinoPageTransitionsBuilder(),
+        // iOS/macOS come from the SDK defaults — see the note at the top.
+        ...const PageTransitionsTheme().builders,
+        TargetPlatform.android: const SharedAxisPageTransitionsBuilder(),
+        TargetPlatform.fuchsia: const SharedAxisPageTransitionsBuilder(),
+        TargetPlatform.linux: const SharedAxisPageTransitionsBuilder(),
+        TargetPlatform.windows: const SharedAxisPageTransitionsBuilder(),
       },
     ),
   );