v6: retry indefinitely with backoff, never drop detections

- Remove 5-attempt drop limit — retry forever until success
- Exponential backoff for retries: 5s → 10s → 20s → 40s → 60s (capped)
- Only drop detections if queue exceeds 2000 (memory protection)
- Drop oldest first when over limit (FIFO eviction)
- Show retry countdown in error message
- Reset backoff on successful send

Handles intermittent 502s from ADAMaps gracefully by holding queue
until server recovers.

app/src/main/java/com/adamaps/varroa/service/ForwardingService.kt

@@ -41,11 +41,16 @@ class ForwardingService : LifecycleService() {
         const val ACTION_START = "com.adamaps.varroa.START_FORWARDING"
         const val ACTION_STOP  = "com.adamaps.varroa.STOP_FORWARDING"
 
-        // Exponential backoff constants
+        // Exponential backoff constants (Bee polling)
         private const val MIN_BACKOFF_MS = 5_000L      // 5 seconds
         private const val MAX_BACKOFF_MS = 60_000L     // 60 seconds
         private const val BACKOFF_MULTIPLIER = 2.0
 
+        // ADAMaps retry queue constants
+        private const val RETRY_MIN_BACKOFF_MS = 5_000L    // 5 seconds
+        private const val RETRY_MAX_BACKOFF_MS = 60_000L   // 60 seconds (cap)
+        private const val MAX_QUEUE_SIZE = 2000            // Max detections to hold in memory
+
         // Shared state exposed to ViewModels
         private val _stats = MutableStateFlow(SessionStats())
         val stats: StateFlow<SessionStats> = _stats.asStateFlow()
@@ -75,17 +80,18 @@ class ForwardingService : LifecycleService() {
     private var reachJob: Job? = null
     private var retryJob: Job? = null
 
-    // Exponential backoff state
+    // Exponential backoff state (Bee polling)
     private var currentBackoffMs = MIN_BACKOFF_MS
     private var consecutiveFailures = 0
 
     // Retry queue for failed ADAMaps sends
     private val pendingQueue = ConcurrentLinkedQueue<QueuedIngest>()
+    private var retryBackoffMs = RETRY_MIN_BACKOFF_MS
+    private var retryConsecutiveFailures = 0
 
     private data class QueuedIngest(
         val deviceId: String,
-        val detections: List<BeeDetection>,
-        var attempts: Int = 0
+        val detections: List<BeeDetection>
     )
 
     override fun onCreate() {
@@ -173,7 +179,8 @@ class ForwardingService : LifecycleService() {
         retryJob?.cancel()
         retryJob = lifecycleScope.launch {
             while (true) {
-                delay(10_000L) // Check retry queue every 10 seconds
+                // Use exponential backoff: 5s → 10s → 20s → 40s → 60s (capped)
+                delay(retryBackoffMs)
                 processRetryQueue()
             }
         }
@@ -256,26 +263,56 @@ class ForwardingService : LifecycleService() {
             is ApiResult.Success -> {
                 _stats.update { it.copy(sent = it.sent + detections.size, queued = it.queued - detections.size) }
                 _adamapsReachable.value = true
+                // Reset retry backoff on direct success
+                retryConsecutiveFailures = 0
+                retryBackoffMs = RETRY_MIN_BACKOFF_MS
             }
             is ApiResult.Error -> {
                 _lastError.value = "ADAMaps: ${result.message}"
                 _adamapsReachable.value = false
                 // Add to retry queue instead of losing detections
                 pendingQueue.add(QueuedIngest(deviceId, detections))
-                // Keep queued count accurate
+                
+                // Enforce max queue size — drop OLDEST if over limit
+                enforceQueueLimit()
             }
         }
     }
 
+    /** Drop oldest detections if queue exceeds MAX_QUEUE_SIZE to prevent OOM */
+    private fun enforceQueueLimit() {
+        var totalQueued = pendingQueue.sumOf { it.detections.size }
+        var dropped = 0
+        
+        while (totalQueued > MAX_QUEUE_SIZE && pendingQueue.isNotEmpty()) {
+            val oldest = pendingQueue.poll() ?: break
+            dropped += oldest.detections.size
+            totalQueued -= oldest.detections.size
+        }
+        
+        if (dropped > 0) {
+            _stats.update { it.copy(queued = it.queued - dropped) }
+            _lastError.value = "Queue full: dropped $dropped oldest detections"
+        }
+    }
+
     private suspend fun processRetryQueue() {
-        if (pendingQueue.isEmpty() || !_adamapsReachable.value) return
+        if (pendingQueue.isEmpty()) return
 
-        val toRetry = mutableListOf<QueuedIngest>()
-        while (pendingQueue.isNotEmpty()) {
-            pendingQueue.poll()?.let { toRetry.add(it) }
+        // Don't retry if ADAMaps is known to be down — wait for reachability check
+        if (!_adamapsReachable.value) {
+            // Increase backoff while waiting
+            retryConsecutiveFailures++
+            retryBackoffMs = min(
+                (RETRY_MIN_BACKOFF_MS * Math.pow(BACKOFF_MULTIPLIER, retryConsecutiveFailures.toDouble())).toLong(),
+                RETRY_MAX_BACKOFF_MS
+            )
+            return
         }
 
-        for (item in toRetry) {
+        // Take one batch at a time (oldest first) to avoid blocking on large queues
+        val item = pendingQueue.poll() ?: return
+
         // Server expects flat array of detections, each with device_id embedded
         val request = item.detections.map { it.toAdaMapsDetection(item.deviceId) }
 
@@ -288,19 +325,24 @@ class ForwardingService : LifecycleService() {
                     ) 
                 }
                 _adamapsReachable.value = true
+                // Reset backoff on success
+                retryConsecutiveFailures = 0
+                retryBackoffMs = RETRY_MIN_BACKOFF_MS
+                _lastError.value = null
             }
             is ApiResult.Error -> {
-                    item.attempts++
-                    if (item.attempts < 5) {
-                        // Re-queue for retry (max 5 attempts)
+                // Always re-queue — never drop detections (except for max queue size)
                 pendingQueue.add(item)
-                    } else {
-                        // Give up after 5 attempts, remove from queued count
-                        _stats.update { it.copy(queued = it.queued - item.detections.size) }
-                        _lastError.value = "Dropped ${item.detections.size} detections after 5 failed attempts"
-                    }
                 _adamapsReachable.value = false
-                }
+                
+                // Increase backoff: 5s → 10s → 20s → 40s → 60s (capped)
+                retryConsecutiveFailures++
+                retryBackoffMs = min(
+                    (RETRY_MIN_BACKOFF_MS * Math.pow(BACKOFF_MULTIPLIER, retryConsecutiveFailures.toDouble())).toLong(),
+                    RETRY_MAX_BACKOFF_MS
+                )
+                
+                _lastError.value = "ADAMaps: ${result.message} (retry in ${retryBackoffMs / 1000}s)"
             }
         }
     }