perf: Phase 4 Android performance optimizations

- frequentEmojis: computed List → cached StateFlow (avoids parse+sort on every recomposition)
- SdkNodeRepositoryImpl: SharingStarted.Eagerly → WhileSubscribed(5_000) for ourNodeInfo, myId, localStats
- PacketRepositoryImpl: deduplicate flatMapLatest chains via shared combine(myNodeNumFlow, currentDb)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

core/data/src/commonMain/kotlin/org/meshtastic/core/data/repository/PacketRepositoryImpl.kt

@@ -21,6 +21,7 @@ import androidx.paging.PagingConfig
 import androidx.paging.PagingData
 import androidx.paging.map
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.map
@@ -61,12 +62,15 @@ class PacketRepositoryImpl(
         .map { it?.myNodeNum ?: 0 }
         .distinctUntilChanged()
 
-    override fun getWaypoints(): Flow<List<DataPacket>> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getAllWaypointsFlow(num) } }
+    /** Cached upstream combining myNodeNum + currentDb — avoids creating duplicate flatMapLatest chains. */
+    private val numAndDb = combine(myNodeNumFlow, dbManager.currentDb) { num, db -> num to db }
+
+    override fun getWaypoints(): Flow<List<DataPacket>> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getAllWaypointsFlow(num) }
         .map { list -> list.map { it.data } }
 
-    override fun getContacts(): Flow<Map<String, DataPacket>> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getContactKeys(num) } }
+    override fun getContacts(): Flow<Map<String, DataPacket>> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getContactKeys(num) }
         .map { map -> map.mapValues { it.value.data } }
 
     override fun getContactsPaged(): Flow<PagingData<DataPacket>> = Pager(
@@ -87,17 +91,17 @@ class PacketRepositoryImpl(
     override suspend fun getUnreadCount(contact: String): Int =
         withContext(dispatchers.io) { dbManager.currentDb.value.packetDao().getUnreadCount(currentMyNodeNum, contact) }
 
-    override fun getUnreadCountFlow(contact: String): Flow<Int> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getUnreadCountFlow(num, contact) } }
+    override fun getUnreadCountFlow(contact: String): Flow<Int> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getUnreadCountFlow(num, contact) }
 
-    override fun getFirstUnreadMessageUuid(contact: String): Flow<Long?> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getFirstUnreadMessageUuid(num, contact) } }
+    override fun getFirstUnreadMessageUuid(contact: String): Flow<Long?> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getFirstUnreadMessageUuid(num, contact) }
 
-    override fun hasUnreadMessages(contact: String): Flow<Boolean> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().hasUnreadMessages(num, contact) } }
+    override fun hasUnreadMessages(contact: String): Flow<Boolean> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().hasUnreadMessages(num, contact) }
 
-    override fun getUnreadCountTotal(): Flow<Int> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getUnreadCountTotal(num) } }
+    override fun getUnreadCountTotal(): Flow<Int> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getUnreadCountTotal(num) }
 
     override suspend fun clearUnreadCount(contact: String, timestamp: Long) =
         withContext(dispatchers.io) { dbManager.currentDb.value.packetDao().clearUnreadCount(currentMyNodeNum, contact, timestamp) }
@@ -463,8 +467,8 @@ class PacketRepositoryImpl(
     suspend fun updateReaction(reaction: RoomReaction) =
         withContext(dispatchers.io) { dbManager.currentDb.value.packetDao().update(reaction) }
 
-    override fun getFilteredCountFlow(contactKey: String): Flow<Int> = myNodeNumFlow
-        .flatMapLatest { num -> dbManager.currentDb.flatMapLatest { db -> db.packetDao().getFilteredCountFlow(num, contactKey) } }
+    override fun getFilteredCountFlow(contactKey: String): Flow<Int> = numAndDb
+        .flatMapLatest { (num, db) -> db.packetDao().getFilteredCountFlow(num, contactKey) }
 
     override suspend fun getFilteredCount(contactKey: String): Int =
         withContext(dispatchers.io) { dbManager.currentDb.value.packetDao().getFilteredCount(currentMyNodeNum, contactKey) }

core/data/src/commonMain/kotlin/org/meshtastic/core/data/repository/SdkNodeRepositoryImpl.kt

@@ -99,15 +99,15 @@ class SdkNodeRepositoryImpl(
 
     override val ourNodeInfo: StateFlow<Node?> =
         combine(_nodeDBbyNum, _myNodeNum) { db, myNum -> myNum?.let { db[it] } }
-            .stateIn(scope, SharingStarted.Eagerly, null)
+            .stateIn(scope, SharingStarted.WhileSubscribed(5_000), null)
 
     override val myId: StateFlow<String?> =
         ourNodeInfo.map { it?.user?.id }
-            .stateIn(scope, SharingStarted.Eagerly, null)
+            .stateIn(scope, SharingStarted.WhileSubscribed(5_000), null)
 
     override val localStats: StateFlow<LocalStats> =
         localStatsDataSource.localStatsFlow
-            .stateIn(scope, SharingStarted.Eagerly, LocalStats())
+            .stateIn(scope, SharingStarted.WhileSubscribed(5_000), LocalStats())
 
     override fun updateLocalStats(stats: LocalStats) {
         scope.launch { localStatsDataSource.setLocalStats(stats) }

feature/messaging/src/commonMain/kotlin/org/meshtastic/feature/messaging/Message.kt

@@ -401,7 +401,7 @@ fun MessageScreen(
                     onSendMessage = { text, key -> viewModel.sendMessage(text, key) },
                     onReply = { message -> replyingToPacketId = message?.packetId },
                 ),
-                quickEmojis = viewModel.frequentEmojis,
+                quickEmojis = viewModel.frequentEmojis.collectAsStateWithLifecycle().value,
             )
             // Show FAB if we can scroll towards the newest messages (index 0).
             if (listState.canScrollBackward) {

feature/messaging/src/commonMain/kotlin/org/meshtastic/feature/messaging/MessageViewModel.kt

@@ -30,6 +30,7 @@ import kotlinx.coroutines.flow.emitAll
 import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.update
 import org.koin.core.annotation.KoinViewModel
 import org.meshtastic.core.common.util.ioDispatcher
@@ -105,17 +106,21 @@ class MessageViewModel(
             }
             .cachedIn(viewModelScope)
 
-    val frequentEmojis: List<String>
-        get() =
-            customEmojiPrefs.customEmojiFrequency.value
-                ?.split(",")
-                ?.associate { entry ->
-                    entry.split("=", limit = 2).takeIf { it.size == 2 }?.let { it[0] to it[1].toInt() } ?: ("" to 0)
-                }
-                ?.toList()
-                ?.sortedByDescending { it.second }
-                ?.map { it.first }
-                ?.take(6) ?: listOf("👍", "👎", "😂", "🔥", "❤️", "😮")
+    private val defaultEmojis = listOf("👍", "👎", "😂", "🔥", "❤️", "😮")
+
+    val frequentEmojis: StateFlow<List<String>> =
+        customEmojiPrefs.customEmojiFrequency
+            .map { raw ->
+                raw?.split(",")
+                    ?.associate { entry ->
+                        entry.split("=", limit = 2).takeIf { it.size == 2 }?.let { it[0] to it[1].toInt() } ?: ("" to 0)
+                    }
+                    ?.toList()
+                    ?.sortedByDescending { it.second }
+                    ?.map { it.first }
+                    ?.take(6) ?: defaultEmojis
+            }
+            .stateInWhileSubscribed(defaultEmojis)
 
     val homoglyphEncodingEnabled = homoglyphEncodingPrefs.homoglyphEncodingEnabled
 

feature/messaging/src/commonTest/kotlin/org/meshtastic/feature/messaging/MessageViewModelTest.kt

@@ -172,8 +172,7 @@ class MessageViewModelTest {
     fun testFrequentEmojis() = runTest {
         customEmojiFrequencyFlow.value = "👍=10,👎=5,😂=20"
 
-        // frequentEmojis is a property, not a flow.
-        val emojis = viewModel.frequentEmojis
+        val emojis = viewModel.frequentEmojis.value
         assertEquals(listOf("😂", "👍", "👎"), emojis)
     }