V3-12: crash reporting (code only)

shouldInitializeCrashReporting() and scrubExtra() are pure, fully unit-tested decision/scrubbing functions wired into sentry_flutter via beforeSend/beforeBreadcrumb. Config.crashReportingEnabled defaults off; the DSN is a compile-time --dart-define, not a preference. RecordingEngine gained an injected onUnexpectedStop callback, firing once when restoreAfterProcessDeath finds a trip still 'recording' at launch -- the process died without a user stop.

Marked partially done: the ticket's real acceptance criteria (a forced crash landing in a real Sentry project from a release build, inspecting a real payload) need a Sentry account and a release build this environment can't produce.

test/recording_engine_test.dart

@@ -336,6 +336,50 @@ void main() {
           reason: 'the dead time is a real gap and must render as one');
     });
 
+    test('a recording trip found at restart reports an unexpected stop (V3-12)',
+        () async {
+      await engine.start();
+      await ride(5);
+      await engine.dispose();
+
+      String? reportedReason;
+      final revived = RecordingEngine(
+        repository: repo,
+        locationSource: source,
+        clock: () => fakeNow,
+        onUnexpectedStop: (reason) => reportedReason = reason,
+      );
+      addTearDown(revived.dispose);
+
+      fakeNow = 20000;
+      await revived.restoreAfterProcessDeath();
+
+      expect(reportedReason, isNotNull,
+          reason: 'the recording stopped without anyone choosing that -- the exact '
+              'failure V3-12 exists to surface');
+    });
+
+    test('a cleanly-completed trip reports nothing at restart', () async {
+      await engine.start();
+      await ride(5);
+      await engine.stop();
+      await engine.dispose();
+
+      var called = false;
+      final revived = RecordingEngine(
+        repository: repo,
+        locationSource: source,
+        clock: () => fakeNow,
+        onUnexpectedStop: (_) => called = true,
+      );
+      addTearDown(revived.dispose);
+
+      await revived.restoreAfterProcessDeath();
+
+      expect(called, isFalse,
+          reason: 'a rider who pressed Stop is not a crash and must not be reported');
+    });
+
     test('the dead time is never measured as distance', () async {
       // The bug this guards is in the native app: after a crash the open segment is
       // adopted rather than closed, so computeSummary -- the authoritative pass at trip