feat(android): bound MetadataProvider on-miss fetches to 4 concurrent

android/app/src/main/java/com/fabledsword/minstrel/metadata/MetadataProvider.kt

@@ -15,10 +15,14 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Semaphore
+import kotlinx.coroutines.sync.withPermit
 import java.util.concurrent.ConcurrentHashMap
 import javax.inject.Inject
 import javax.inject.Singleton
 
+private const val MAX_CONCURRENT_FETCHES = 4
+
 /**
  * Cache-first metadata reads with eager on-miss live-fetch.
  *
@@ -49,6 +53,12 @@ class MetadataProvider @Inject constructor(
     private val inFlightArtists = ConcurrentHashMap<String, Job>()
     private val inFlightTracks = ConcurrentHashMap<String, Job>()
 
+    // Caps concurrent on-miss fetches so a cold Home (~30 tiles) doesn't
+    // fire ~30 parallel /api calls. Mirrors Flutter HydrationQueue's
+    // _maxConcurrent = 4. Per-id dedup (above) is orthogonal: the gate
+    // bounds distinct-id fetches; extras suspend on the semaphore.
+    private val fetchGate = Semaphore(MAX_CONCURRENT_FETCHES)
+
     /**
      * Live AlbumRef? for [id]. Fires a background fetch the first
      * time the cache emits null. Safe to subscribe concurrently from
@@ -98,7 +108,7 @@ class MetadataProvider @Inject constructor(
     ): Job = inFlight.computeIfAbsent(id) {
         appScope.launch {
             try {
-                block()
+                fetchGate.withPermit { block() }
             } catch (
                 @Suppress("TooGenericExceptionCaught", "SwallowedException") e: Throwable,
             ) {