fix: set demangleStackTrace to handle async chain stack traces

When zone errors bubble up through Dart's async machinery the stack
trace is in package:stack_trace chain format (with '===== asynchronous
gap =====' separators). Flutter's StackFrame parser asserts on those
lines. FlutterError.demangleStackTrace strips the chain format back to
a plain VM trace before Flutter tries to parse it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/main.dart

@@ -12,6 +12,7 @@ import 'package:sharedinbox/data/db/database.dart';
 import 'package:sharedinbox/di.dart';
 import 'package:sharedinbox/ui/router.dart';
 import 'package:sharedinbox/ui/screens/crash_screen.dart';
+import 'package:stack_trace/stack_trace.dart' as stack_trace;
 
 void main({List<Override> overrides = const []}) {
   unawaited(
@@ -19,6 +20,15 @@ void main({List<Override> overrides = const []}) {
       () async {
         WidgetsFlutterBinding.ensureInitialized();
 
+        // Dart's async machinery propagates stack traces in chain format
+        // (with '===== asynchronous gap =====' separators). Flutter's
+        // StackFrame parser asserts on those lines, so strip them first.
+        FlutterError.demangleStackTrace = (StackTrace s) {
+          if (s is stack_trace.Chain) return s.toTrace().vmTrace;
+          if (s is stack_trace.Trace) return s.vmTrace;
+          return s;
+        };
+
         // Catch errors during build (e.g. layout exceptions) and show CrashScreen.
         ErrorWidget.builder = (details) => CrashScreen(
               exception: details.exception,

pubspec.lock

@@ -1021,7 +1021,7 @@ packages:
     source: hosted
     version: "0.44.4"
   stack_trace:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: stack_trace
       sha256: "8b27215b45d22309b5cddda1aa2b19bdfec9df0e765f2de506401c071d38d1b1"

pubspec.yaml

@@ -58,6 +58,9 @@ dependencies:
   flutter_local_notifications: ^21.0.0
   workmanager: ^0.9.0
 
+  # Stack trace chain-to-VM conversion for FlutterError.demangleStackTrace
+  stack_trace: ^1.12.1
+
   # App version metadata for crash reports
   package_info_plus: ^10.1.0
   share_plus: ^13.1.0