Throttle conditions API; delay particle view until data loaded

loadConditions now skips the API call if conditions were loaded
< 5 min ago and position hasn't moved > 2 nm — prevents 429 from
overlapping triggers (startup backstop, GPS first-fix, camera idle).
Dev log shows "conditions: skip age=Xs dist=Y.Znm" when throttled.

ParticleWindView starts hidden and is revealed only when the first
windArrow value arrives, so particles don't flash before the map loads.

https://claude.ai/code/session_01HXPjBsogsJVRwCiekDGkJX

2 files changed, 31 insertions, 5 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 35a0e91..b7db246 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
@@ -400,10 +400,8 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
         mapView = findViewById(R.id.mapView)
         particleWindView = findViewById(R.id.particle_wind_view)
 
-        // Apply persisted particles preference immediately
-        if (!layerManager.particlesEnabled) {
-            particleWindView?.visibility = View.GONE
-        }
+        // Always start hidden; revealed by the windArrow observer once data arrives
+        particleWindView?.visibility = View.GONE
 
         if (NavApplication.isTesting) return
 
@@ -503,6 +501,9 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
                 if (arrow != null) {
                     mapHandler?.updateWindLayer(arrow)
                     particleWindView?.setWind(arrow.directionDeg, arrow.speedKt)
+                    if (layerManager.particlesEnabled) {
+                        particleWindView?.visibility = View.VISIBLE
+                    }
                 }
             }
         }
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 e65cbd1..868b828 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
@@ -170,11 +170,27 @@ class MainViewModel(
             .create(AisHubApiService::class.java)
     }
 
+    private var lastConditionsLat = Double.NaN
+    private var lastConditionsLon = Double.NaN
+    private var lastConditionsMs  = 0L
+
     /**
      * Fetches current conditions snapshot for [lat]/[lon] and exposes it via [marineConditions].
-     * Silently ignored on network failure — the UI keeps showing dashes.
+     * Throttled: skips if conditions loaded < 5 min ago and position < 2 nm from last load.
      */
     fun loadConditions(lat: Double, lon: Double) {
+        val nowMs  = System.currentTimeMillis()
+        val ageMs  = nowMs - lastConditionsMs
+        val distNm = if (lastConditionsLat.isNaN()) Double.MAX_VALUE
+                     else distanceNm(lastConditionsLat, lastConditionsLon, lat, lon)
+        if (ageMs < 5 * 60_000L && distNm < 2.0) {
+            NavLogger.i("conditions", "skip age=${ageMs / 1000}s dist=%.1fnm".format(distNm))
+            return
+        }
+        lastConditionsLat = lat
+        lastConditionsLon = lon
+        lastConditionsMs  = nowMs
+
         conditionsJob?.cancel()
         conditionsJob = viewModelScope.launch {
             _conditionsLoading.value = true
@@ -192,6 +208,15 @@ class MainViewModel(
         }
     }
 
+    private fun distanceNm(lat1: Double, lon1: Double, lat2: Double, lon2: Double): Double {
+        val dLat = Math.toRadians(lat2 - lat1)
+        val dLon = Math.toRadians(lon2 - lon1)
+        val a = sin(dLat / 2) * sin(dLat / 2) +
+                cos(Math.toRadians(lat1)) * cos(Math.toRadians(lat2)) *
+                sin(dLon / 2) * sin(dLon / 2)
+        return 3440.065 * 2 * kotlin.math.asin(kotlin.math.sqrt(a))
+    }
+
     /**
      * Fetch weather and wind arrow for [lat]/[lon]. Called once on first GPS fix.
      */