feat(cache): cache profile metadata and follower/following counts

Profile screen now reads initial values from cache so navigating back
shows data instantly instead of re-fetching everything from scratch.

- Seed displayName/about/picture from User.metadataOrNull() on compose
- Add followerCounts/followingCounts maps to DesktopLocalCache
- Write counts on each update, read on profile open
- Follower count still ticks up live (good UX) but starts from cached value
- 4 new tests for profile count caching + metadata cache reads

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/cache/DesktopLocalCache.kt

@@ -491,6 +491,29 @@ class DesktopLocalCache : ICacheProvider {
         eventStream.emitDeletedNotes(notes)
     }
 
+    // ----- Profile count cache -----
+
+    private val followerCounts = ConcurrentHashMap<HexKey, Int>()
+    private val followingCounts = ConcurrentHashMap<HexKey, Int>()
+
+    fun getCachedFollowerCount(pubkey: HexKey): Int = followerCounts[pubkey] ?: 0
+
+    fun getCachedFollowingCount(pubkey: HexKey): Int = followingCounts[pubkey] ?: 0
+
+    fun cacheFollowerCount(
+        pubkey: HexKey,
+        count: Int,
+    ) {
+        followerCounts[pubkey] = count
+    }
+
+    fun cacheFollowingCount(
+        pubkey: HexKey,
+        count: Int,
+    ) {
+        followingCounts[pubkey] = count
+    }
+
     // ----- Stats -----
 
     fun userCount(): Int = users.size()
@@ -503,6 +526,8 @@ class DesktopLocalCache : ICacheProvider {
         addressableNotes.clear()
         deletedEvents.clear()
         _followedUsers.value = emptySet()
+        followerCounts.clear()
+        followingCounts.clear()
     }
 }
 

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/UserProfileScreen.kt

@@ -127,12 +127,22 @@ fun UserProfileScreen(
     val relayStatuses by relayManager.relayStatuses.collectAsState()
     val connectedRelays = remember(relayStatuses) { relayStatuses.keys }
 
-    // User metadata
-    var displayName by remember { mutableStateOf<String?>(null) }
-    var about by remember { mutableStateOf<String?>(null) }
-    var picture by remember { mutableStateOf<String?>(null) }
-    var followersCount by remember { mutableStateOf(0) }
-    var followingCount by remember { mutableStateOf(0) }
+    // User metadata — seed from cache so returning to profile is instant
+    val cachedUser = remember(pubKeyHex) { localCache.getUserIfExists(pubKeyHex) }
+    val cachedMetadata = remember(pubKeyHex) { cachedUser?.metadataOrNull() }
+    var displayName by remember { mutableStateOf(cachedMetadata?.bestName()) }
+    var about by remember {
+        mutableStateOf(
+            cachedMetadata
+                ?.flow
+                ?.value
+                ?.info
+                ?.about,
+        )
+    }
+    var picture by remember { mutableStateOf(cachedMetadata?.profilePicture()) }
+    var followersCount by remember { mutableStateOf(localCache.getCachedFollowerCount(pubKeyHex)) }
+    var followingCount by remember { mutableStateOf(localCache.getCachedFollowingCount(pubKeyHex)) }
 
     // Profile editing state (only for own profile)
     val isOwnProfile = account != null && pubKeyHex == account.pubKeyHex
@@ -279,8 +289,9 @@ fun UserProfileScreen(
                 pubKeyHex = pubKeyHex,
                 onEvent = { event, _, _, _ ->
                     if (event is ContactListEvent) {
-                        // Count the number of people this user follows
-                        followingCount = event.verifiedFollowKeySet().size
+                        val count = event.verifiedFollowKeySet().size
+                        followingCount = count
+                        localCache.cacheFollowingCount(pubKeyHex, count)
                     }
                 },
                 onEose = { _, _ -> },
@@ -314,7 +325,9 @@ fun UserProfileScreen(
                 onEvent = { event, _, _, _ ->
                     // Count unique authors who follow this user
                     if (followerAuthors.add(event.pubKey)) {
-                        followersCount = followerAuthors.size
+                        val count = followerAuthors.size
+                        followersCount = count
+                        localCache.cacheFollowerCount(pubKeyHex, count)
                     }
                 },
                 onEose = { _, _ -> },