T19/T21: map and export, completing Phase 4

flutter_map with the same OSM tiles and no-API-key reasoning that chose osmdroid.
All four load-bearing behaviours ported and, unlike the native app's map, tested:
one polyline per segment so a pause is a real gap, render-only decimation, the
zoom clamp at OSM's max tile zoom with a short-ride fallback, and a real user
agent. Speed colouring is bucketed per run rather than per-vertex, since neither
osmdroid nor flutter_map makes per-vertex paint reasonable.

Export via share_plus, which also handles the iPad popover anchor a naive port
forgets. It passes the raw stored points, never the map's decimated path.

164 tests passing, analyze clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/src/recording/geolocator_location_source.dart

@@ -68,15 +68,14 @@ class GeolocatorLocationSource implements LocationSource {
 
     await _ensurePermission();
 
-    _subscription = Geolocator.getPositionStream(
-      locationSettings: _settings(),
-    ).listen(
-      (p) => _controller.add(_toFix(p)),
-      // A transient platform error must not close the stream: the engine treats a closed
-      // stream as "recording stopped", which is a user-visible event.
-      onError: (Object _) {},
-      cancelOnError: false,
-    );
+    _subscription = Geolocator.getPositionStream(locationSettings: _settings())
+        .listen(
+          (p) => _controller.add(_toFix(p)),
+          // A transient platform error must not close the stream: the engine treats a closed
+          // stream as "recording stopped", which is a user-visible event.
+          onError: (Object _) {},
+          cancelOnError: false,
+        );
   }
 
   @override
@@ -153,12 +152,12 @@ class GeolocatorLocationSource implements LocationSource {
   }
 
   LocationFix _toFix(Position p) => LocationFix(
-        timestamp: p.timestamp.millisecondsSinceEpoch,
-        latitude: p.latitude,
-        longitude: p.longitude,
-        speedMps: p.speed,
-        altitudeM: p.altitude,
-        accuracyM: p.accuracy,
-        bearingDeg: p.heading,
-      );
+    timestamp: p.timestamp.millisecondsSinceEpoch,
+    latitude: p.latitude,
+    longitude: p.longitude,
+    speedMps: p.speed,
+    altitudeM: p.altitude,
+    accuracyM: p.accuracy,
+    bearingDeg: p.heading,
+  );
 }

lib/src/recording/location_source.dart

@@ -67,7 +67,8 @@ class LocationException implements Exception {
   final String? message;
 
   @override
-  String toString() => 'LocationException($failure${message == null ? '' : ': $message'})';
+  String toString() =>
+      'LocationException($failure${message == null ? '' : ': $message'})';
 }
 
 /// A source of GPS fixes.
@@ -154,14 +155,15 @@ class FakeLocationSource implements LocationSource {
     double altitudeM = 1000.0,
     double accuracyM = 5.0,
     double bearingDeg = 0.0,
-  }) =>
-      emit(LocationFix(
-        timestamp: timestamp,
-        latitude: latitude,
-        longitude: longitude,
-        speedMps: speedMps,
-        altitudeM: altitudeM,
-        accuracyM: accuracyM,
-        bearingDeg: bearingDeg,
-      ));
+  }) => emit(
+    LocationFix(
+      timestamp: timestamp,
+      latitude: latitude,
+      longitude: longitude,
+      speedMps: speedMps,
+      altitudeM: altitudeM,
+      accuracyM: accuracyM,
+      bearingDeg: bearingDeg,
+    ),
+  );
 }

lib/src/recording/recording_engine.dart

@@ -55,10 +55,10 @@ class RecordingEngine {
     required LocationSource locationSource,
     LiveTelemetry? liveTelemetry,
     int Function()? clock,
-  })  : _repo = repository,
-        _source = locationSource,
-        _live = liveTelemetry ?? LiveTelemetry.instance,
-        _now = clock ?? (() => DateTime.now().millisecondsSinceEpoch);
+  }) : _repo = repository,
+       _source = locationSource,
+       _live = liveTelemetry ?? LiveTelemetry.instance,
+       _now = clock ?? (() => DateTime.now().millisecondsSinceEpoch);
 
   final TripRepository _repo;
   final LocationSource _source;
@@ -265,20 +265,20 @@ class RecordingEngine {
 
   /// One flush cycle: take up to [flushSize] buffered points and write them.
   Future<void> _flush() => _writeLock.synchronized(() async {
-        if (_pending.isEmpty) return;
-        final take = _pending.length < flushSize ? _pending.length : flushSize;
-        final batch = _pending.sublist(0, take);
-        _pending.removeRange(0, take);
-        await _persist(batch);
-      });
+    if (_pending.isEmpty) return;
+    final take = _pending.length < flushSize ? _pending.length : flushSize;
+    final batch = _pending.sublist(0, take);
+    _pending.removeRange(0, take);
+    await _persist(batch);
+  });
 
   /// Writes everything currently queued and returns once it has landed.
   Future<void> _drain() => _writeLock.synchronized(() async {
-        if (_pending.isEmpty) return;
-        final batch = List<TrackPoint>.from(_pending);
-        _pending.clear();
-        await _persist(batch);
-      });
+    if (_pending.isEmpty) return;
+    final batch = List<TrackPoint>.from(_pending);
+    _pending.clear();
+    await _persist(batch);
+  });
 
   Future<void> _persist(List<TrackPoint> points) async {
     if (points.isEmpty) return;