feat(ground-suite): redesign observability console

ground-suite/test/features/observability/observability_controller_test.dart

@@ -93,10 +93,72 @@ void main() {
     expect(state.parserDropCount, 0);
     expect(state.semanticDropCount, 0);
   });
+
+  test(
+    'bounds diagnostics while telemetry stays outside the timeline',
+    () async {
+      final port = _ControlledDataPort();
+      final container = ProviderContainer(
+        overrides: [vehicleDataPortProvider.overrideWithValue(port)],
+      );
+      addTearDown(container.dispose);
+
+      container.read(observabilityControllerProvider);
+      await Future<void>.delayed(Duration.zero);
+
+      port.events.add(
+        ObservationReceived(
+          ErrorEvent(
+            receivedAt: DateTime.utc(2026, 8, 10),
+            path: 'kaptan_drivers::lidar_lite_v3::error::Error::TransferFault',
+          ),
+        ),
+      );
+      port.events.add(
+        ObservationReceived(
+          HeartbeatEvent(
+            receivedAt: DateTime.utc(2026, 8, 10, 0, 0, 1),
+            systemId: 7,
+            componentId: 42,
+            armed: false,
+            vehicleState: 'Standby',
+          ),
+        ),
+      );
+      for (var index = 0; index < 501; index++) {
+        port.events.add(
+          ObservationReceived(
+            TelemetryEvent(
+              receivedAt: DateTime.utc(2026, 8, 10, 0, 0, index % 60),
+              kind: TelemetryKind.rawImu,
+            ),
+          ),
+        );
+      }
+      for (var index = 0; index < 500; index++) {
+        port.events.add(
+          ObservationReceived(
+            LogEvent(
+              receivedAt: DateTime.utc(2026, 8, 10, 0, 1, index % 60),
+              level: MavSeverity.info,
+              message: 'Diagnostic $index',
+            ),
+          ),
+        );
+      }
+
+      final state = container.read(observabilityControllerProvider);
+      expect(state.events, hasLength(500));
+      expect(state.localTimelineEvictionCount, 1);
+      expect(state.events.whereType<ErrorEvent>(), hasLength(1));
+      expect(state.lastHeartbeat?.systemId, 7);
+      expect(state.observedTelemetryKinds, contains(TelemetryKind.rawImu));
+    },
+  );
 }
 
 class _ControlledDataPort implements VehicleDataPort {
-  final events = StreamController<VehicleDataUpdate>();
+  final events = StreamController<VehicleDataUpdate>(sync: true);
 
   @override
   bool get isReplay => false;