Week 3 Day 19: Fix CI (assets + lint), validate HEAD sync, and update timeline

Author: Anbu-00001

PROJECT_TIMELINE.txt

@@ -1053,4 +1053,17 @@ Files Created/Modified:
 Notes:
 - Full system verification (Day 15-18) successfully passed, confirming P2P broadcast, deduplication, sync, and causal consistency.
 
+DAY 19:
+Date:
+Focus: Head-Based Synchronization
+
+Content:
+• Implemented HEAD exchange protocol to compare distributed state across peers
+• Built missing message detection using DAG head comparison
+• Added message_request and message_response protocols
+• Ensured forward causal delivery using dependency-aware ordering
+• Integrated sync with GossipLog for consistency-safe application
+• Prevented redundant data transfer by requesting only missing messages
+• Enabled full peer-to-peer state convergence without central server
+
 ------------------------------------------------------------

mobile_app/assets/tiles/.keep

@@ -128,7 +128,7 @@ class IncidentRepository {
       });
     } catch (e) {
       // Failed to push (e.g. offline), keeps 'queued'
-      print('Sync failed, will retry later: $e');
+      debugPrint('Sync failed, will retry later: $e');
     }
   }
 

mobile_app/lib/data/repositories/incident_repository.dart

@@ -504,7 +504,8 @@ class _MapScreenState extends State<MapScreen> {
   void _centerOnMyLocation() async {
     final locService = context.read<LocationService>();
     final loc = await locService.getCurrentLocation();
-    if (loc != null && mounted) {
+    if (!mounted) return;
+    if (loc != null) {
       _mapController.move(loc, 16.0);
     } else {
       ScaffoldMessenger.of(context).showSnackBar(

mobile_app/lib/features/map/map_screen.dart

@@ -60,7 +60,7 @@ final LatLngBounds indiaBounds = LatLngBounds(
 /// Service that manages offline tile serving via MBTiles and tile URL resolution.
 ///
 /// Fallback chain (never leaves tile URL empty):
-/// 1. Local MBTiles server → http://localhost:<port>/tiles/{z}/{x}/{y}.png
+/// 1. Local MBTiles server → http://localhost:[port]/tiles/{z}/{x}/{y}.png
 /// 2. Config remote tile URL from config.json `backend_tile_url`
 /// 3. Hard fallback: https://tile.openstreetmap.org/{z}/{x}/{y}.png
 class MapService {

mobile_app/lib/features/map/map_service.dart

@@ -80,7 +80,7 @@ class NavigationStepsPanel extends StatelessWidget {
                     : ListView.separated(
                         controller: scrollController,
                         itemCount: steps.length,
-                        separatorBuilder: (_, __) => const Divider(height: 1),
+                        separatorBuilder: (context, index) => const Divider(height: 1),
                         itemBuilder: (context, index) {
                           final step = steps[index];
                           final distanceStr = step.distance >= 1000

mobile_app/lib/widgets/navigation_steps_panel.dart

@@ -226,5 +226,67 @@ void main() {
       expect(received[1].msgId, 'm2');
       expect(received[2].msgId, 'm3');
     });
+
+    test('Day 19 Integration: Multi-device convergence (A -> B -> C)', () async {
+      final serviceA = GossipLogService();
+      final serviceB = GossipLogService();
+      final serviceC = GossipLogService();
+
+      // A creates 3 incidents
+      final m1 = _makeEnvelope(msgId: 'm1', clock: 1);
+      serviceA.recordSent(m1);
+      final m2 = _makeEnvelope(msgId: 'm2', clock: 2, prevMsgIds: ['m1']);
+      serviceA.recordSent(m2);
+      final m3 = _makeEnvelope(msgId: 'm3', clock: 3, prevMsgIds: ['m2']);
+      serviceA.recordSent(m3);
+
+      expect(serviceA.logSize, 3);
+
+      // A connects to B. B discovers it's missing M1, M2, M3.
+      // B sends head_exchange with empty heads. A sends head_exchange with [m3].
+      final missingInB = serviceB.findMissingMessages(serviceA.getHeads());
+      expect(missingInB, ['m3']);
+
+      // B requests m3. A sends m3.
+      final fetched3 = serviceA.fetchAndSortMessages(['m3']);
+      final depsB = serviceB.receive(fetched3.first);
+      expect(depsB, ['m2']);
+
+      // B requests m2. A sends m2.
+      final fetched2 = serviceA.fetchAndSortMessages(['m2']);
+      final depsB2 = serviceB.receive(fetched2.first);
+      expect(depsB2, ['m1']);
+
+      // B requests m1. A sends m1.
+      final fetched1 = serviceA.fetchAndSortMessages(['m1']);
+      final depsB3 = serviceB.receive(fetched1.first);
+      expect(depsB3, isEmpty);
+
+      // B now has all messages
+      expect(serviceB.logSize, 3);
+      expect(serviceB.getHeads(), ['m3']);
+
+      // B connects to C. C only has m1. 
+      serviceC.receive(m1);
+      final missingInC = serviceC.findMissingMessages(serviceB.getHeads());
+      expect(missingInC, ['m3']);
+
+      // C requests m3, receives from B.
+      final fetchedC3 = serviceB.fetchAndSortMessages(['m3']);
+      final depsC = serviceC.receive(fetchedC3.first);
+      expect(depsC, ['m2']);
+
+      // C requests m2, receives from B.
+      final fetchedC2 = serviceB.fetchAndSortMessages(['m2']);
+      final depsC2 = serviceC.receive(fetchedC2.first);
+      expect(depsC2, isEmpty); // C already had m1. So m2 unblocks m3!
+
+      // C now has all messages
+      expect(serviceC.logSize, 3);
+      expect(serviceC.getHeads(), ['m3']);
+
+      expect(serviceA.getHeads(), serviceB.getHeads());
+      expect(serviceB.getHeads(), serviceC.getHeads());
+    });
   });
 }