feat(track): implement GPS track recording with map overlay

- TrackRepository + TrackPoint wired into MainViewModel:
  isRecording/trackPoints StateFlows, startTrack/stopTrack/addGpsPoint
- MapHandler.updateTrackLayer(): lazily initialises a red LineLayer
  and updates GeoJSON polyline from List<TrackPoint>
- fab_record_track FAB in activity_main.xml (top|end of bottom nav);
  icon toggles between ic_track_record and ic_close while recording
- MainActivity feeds every GPS fix into viewModel.addGpsPoint() and
  observes trackPoints to redraw the polyline in real time
- ic_track_record.xml vector drawable (red record dot)
- 8 TrackRepositoryTest tests all GREEN

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

7 files changed, 153 insertions, 3 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
index 61d8b9b..ecaddc0 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
@@ -45,9 +45,11 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     private var instrumentHandler: InstrumentHandler? = null
     private var mapHandler: MapHandler? = null
     private var anchorWatchHandler: AnchorWatchHandler? = null
-    
+    private var loadedStyle: Style? = null
+
     private lateinit var bottomSheetBehavior: BottomSheetBehavior<View>
     private lateinit var fragmentContainer: FrameLayout
+    private lateinit var fabRecordTrack: FloatingActionButton
     private val safetyFragment = SafetyFragment().apply { setSafetyListener(this@MainActivity) }
 
     private val viewModel: MainViewModel by viewModels()
@@ -81,6 +83,11 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
         findViewById<FloatingActionButton>(R.id.fab_mob).setOnClickListener {
             onActivateMob()
         }
+
+        fabRecordTrack = findViewById(R.id.fab_record_track)
+        fabRecordTrack.setOnClickListener {
+            if (viewModel.isRecording.value) viewModel.stopTrack() else viewModel.startTrack()
+        }
     }
 
     private fun setupBottomSheet() {
@@ -227,10 +234,11 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
                     }, 256))
                 .withLayer(RasterLayer("openseamap-layer", "openseamap-source"))
             
-            maplibreMap.setStyle(style) { loadedStyle ->
+            maplibreMap.setStyle(style) { style ->
+                loadedStyle = style
                 val anchorBitmap = rasterizeDrawable(R.drawable.ic_anchor)
                 val arrowBitmap = rasterizeDrawable(R.drawable.ic_tidal_arrow)
-                mapHandler?.setupLayers(loadedStyle, anchorBitmap, arrowBitmap)
+                mapHandler?.setupLayers(style, anchorBitmap, arrowBitmap)
             }
         }
     }
@@ -239,6 +247,8 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
         lifecycleScope.launch {
             LocationService.locationFlow.collect { gpsData ->
                 mapHandler?.centerOnLocation(gpsData.latitude, gpsData.longitude)
+                val sogKnots = gpsData.speedOverGround * 1.94384
+                viewModel.addGpsPoint(gpsData.latitude, gpsData.longitude, sogKnots, gpsData.courseOverGround.toDouble())
             }
         }
         lifecycleScope.launch {
@@ -246,6 +256,19 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
                 safetyFragment.updateAnchorStatus(if (state.isActive) "Active: ${state.watchCircleRadiusMeters}m" else "Inactive")
             }
         }
+        lifecycleScope.launch {
+            viewModel.trackPoints.collect { points ->
+                val style = loadedStyle ?: return@collect
+                mapHandler?.updateTrackLayer(style, points)
+            }
+        }
+        lifecycleScope.launch {
+            viewModel.isRecording.collect { recording ->
+                val icon = if (recording) R.drawable.ic_close else R.drawable.ic_track_record
+                fabRecordTrack.setImageResource(icon)
+                fabRecordTrack.contentDescription = if (recording) "Stop Recording" else "Record Track"
+            }
+        }
     }
 
     private fun startInstrumentSimulation(polarTable: PolarTable) {
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/track/TrackPoint.kt b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackPoint.kt
new file mode 100644
index 0000000..d803c8c
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackPoint.kt
@@ -0,0 +1,12 @@
+package org.terst.nav.track
+
+data class TrackPoint(
+    val lat: Double,
+    val lon: Double,
+    val sogKnots: Double,
+    val cogDeg: Double,
+    val windSpeedKnots: Double,
+    val windAngleDeg: Double,
+    val isTrueWind: Boolean,
+    val timestampMs: Long
+)
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/track/TrackRepository.kt b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackRepository.kt
new file mode 100644
index 0000000..c90adb9
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/track/TrackRepository.kt
@@ -0,0 +1,24 @@
+package org.terst.nav.track
+
+class TrackRepository {
+
+    var isRecording: Boolean = false
+        private set
+
+    private val points = mutableListOf<TrackPoint>()
+
+    fun startTrack() {
+        points.clear()
+        isRecording = true
+    }
+
+    fun stopTrack() {
+        isRecording = false
+    }
+
+    fun addPoint(point: TrackPoint) {
+        if (isRecording) points.add(point)
+    }
+
+    fun getPoints(): List<TrackPoint> = points.toList()
+}
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/MainViewModel.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/MainViewModel.kt
index 8e84e1e..33decbe 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/ui/MainViewModel.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/MainViewModel.kt
@@ -6,6 +6,8 @@ import org.terst.nav.ais.AisHubSource
 import org.terst.nav.ais.AisRepository
 import org.terst.nav.ais.AisVessel
 import org.terst.nav.data.api.AisHubApiService
+import org.terst.nav.track.TrackPoint
+import org.terst.nav.track.TrackRepository
 import org.terst.nav.data.model.ForecastItem
 import org.terst.nav.data.model.WindArrow
 import org.terst.nav.data.repository.WeatherRepository
@@ -43,6 +45,36 @@ class MainViewModel(
 
     private val aisRepository = AisRepository()
 
+    private val trackRepository = TrackRepository()
+
+    private val _isRecording = MutableStateFlow(false)
+    val isRecording: StateFlow<Boolean> = _isRecording.asStateFlow()
+
+    private val _trackPoints = MutableStateFlow<List<TrackPoint>>(emptyList())
+    val trackPoints: StateFlow<List<TrackPoint>> = _trackPoints.asStateFlow()
+
+    fun startTrack() {
+        trackRepository.startTrack()
+        _trackPoints.value = emptyList()
+        _isRecording.value = true
+    }
+
+    fun stopTrack() {
+        trackRepository.stopTrack()
+        _isRecording.value = false
+    }
+
+    fun addGpsPoint(lat: Double, lon: Double, sogKnots: Double, cogDeg: Double) {
+        val point = TrackPoint(
+            lat = lat, lon = lon,
+            sogKnots = sogKnots, cogDeg = cogDeg,
+            windSpeedKnots = 0.0, windAngleDeg = 0.0, isTrueWind = false,
+            timestampMs = System.currentTimeMillis()
+        )
+        trackRepository.addPoint(point)
+        _trackPoints.value = trackRepository.getPoints()
+    }
+
     private val aisHubApi: AisHubApiService by lazy {
         Retrofit.Builder()
             .baseUrl("https://data.aishub.net")
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
index 91569cf..cbc2e90 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/MapHandler.kt
@@ -7,6 +7,7 @@ import org.maplibre.android.geometry.LatLng
 import org.maplibre.android.maps.MapLibreMap
 import org.maplibre.android.maps.Style
 import org.maplibre.android.style.layers.CircleLayer
+import org.maplibre.android.style.layers.LineLayer
 import org.maplibre.android.style.layers.PropertyFactory
 import org.maplibre.android.style.layers.RasterLayer
 import org.maplibre.android.style.layers.SymbolLayer
@@ -15,10 +16,12 @@ import org.maplibre.android.style.sources.RasterSource
 import org.maplibre.android.style.sources.TileSet
 import org.maplibre.geojson.Feature
 import org.maplibre.geojson.FeatureCollection
+import org.maplibre.geojson.LineString
 import org.maplibre.geojson.Point
 import org.maplibre.geojson.Polygon
 import org.terst.nav.AnchorWatchState
 import org.terst.nav.TidalCurrentState
+import org.terst.nav.track.TrackPoint
 import kotlin.math.cos
 import kotlin.math.sin
 
@@ -37,9 +40,13 @@ class MapHandler(private val maplibreMap: MapLibreMap) {
     private val TIDAL_CURRENT_LAYER_ID = "tidal-current-layer"
     private val TIDAL_ARROW_ICON_ID = "tidal-arrow-icon"
 
+    private val TRACK_SOURCE_ID = "track-source"
+    private val TRACK_LAYER_ID = "track-line"
+
     private var anchorPointSource: GeoJsonSource? = null
     private var anchorCircleSource: GeoJsonSource? = null
     private var tidalCurrentSource: GeoJsonSource? = null
+    private var trackSource: GeoJsonSource? = null
 
     /**
      * Initializes map layers for anchor watch and tidal currents.
@@ -127,6 +134,28 @@ class MapHandler(private val maplibreMap: MapLibreMap) {
         }
     }
 
+    /**
+     * Updates the GPS track polyline on the map. Lazily initialises the layer on first call.
+     */
+    fun updateTrackLayer(style: Style, points: List<TrackPoint>) {
+        if (trackSource == null) {
+            trackSource = GeoJsonSource(TRACK_SOURCE_ID)
+            style.addSource(trackSource!!)
+            style.addLayer(LineLayer(TRACK_LAYER_ID, TRACK_SOURCE_ID).apply {
+                setProperties(
+                    PropertyFactory.lineColor("#E53935"),
+                    PropertyFactory.lineWidth(3f)
+                )
+            })
+        }
+        if (points.size >= 2) {
+            val coords = points.map { Point.fromLngLat(it.lon, it.lat) }
+            trackSource?.setGeoJson(Feature.fromGeometry(LineString.fromLngLats(coords)))
+        } else {
+            trackSource?.setGeoJson(FeatureCollection.fromFeatures(emptyList()))
+        }
+    }
+
     private fun createCirclePolygon(lat: Double, lon: Double, radiusMeters: Double): Polygon {
         val points = mutableListOf<Point>()
         val degreesBetweenPoints = 8
diff --git a/android-app/app/src/main/res/drawable/ic_track_record.xml b/android-app/app/src/main/res/drawable/ic_track_record.xml
new file mode 100644
index 0000000..9016369
--- /dev/null
+++ b/android-app/app/src/main/res/drawable/ic_track_record.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <!-- Outer ring -->
+    <path
+        android:fillColor="#00000000"
+        android:strokeColor="@android:color/white"
+        android:strokeWidth="2"
+        android:pathData="M12,12m-10,0a10,10 0,1 1,20 0a10,10 0,1 1,-20 0"/>
+    <!-- Filled red dot -->
+    <path
+        android:fillColor="#E53935"
+        android:pathData="M12,12m-6,0a6,6 0,1 1,12 0a6,6 0,1 1,-12 0"/>
+</vector>
diff --git a/android-app/app/src/main/res/layout/activity_main.xml b/android-app/app/src/main/res/layout/activity_main.xml
index 66d1abe..552bf99 100644
--- a/android-app/app/src/main/res/layout/activity_main.xml
+++ b/android-app/app/src/main/res/layout/activity_main.xml
@@ -68,4 +68,17 @@
         app:layout_anchor="@id/bottom_navigation"
         app:layout_anchorGravity="top|start" />
 
+    <!-- Record Track Button -->
+    <com.google.android.material.floatingactionbutton.FloatingActionButton
+        android:id="@+id/fab_record_track"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_margin="16dp"
+        android:clickable="true"
+        android:focusable="true"
+        android:contentDescription="Record Track"
+        app:srcCompat="@drawable/ic_track_record"
+        app:layout_anchor="@id/bottom_navigation"
+        app:layout_anchorGravity="top|end" />
+
 </androidx.coordinatorlayout.widget.CoordinatorLayout>