improve chat viewport restoration and scrolling precision

- introduce `ChatScrollCommand` for unified handling of viewport restoration, jumping to messages, and scrolling to bottom
- implement `ChatViewportCacheEntry` to store anchor message ID and precise pixel offsets
- add staged scrolling to handle large distance jumps more efficiently
- update `CacheProvider` and `CachePreferences` to persist and retrieve detailed viewport state
- replace simple message ID scrolling with the new command-based system in `ChatContent`
- enhance logic for restoring scroll position when opening chats or topic threads
- optimize viewport snapshot capturing and saving on lifecycle events

Author: gdlbo

domain/src/main/java/org/monogram/domain/models/ChatViewportCacheEntry.kt

@@ -0,0 +1,10 @@
+package org.monogram.domain.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ChatViewportCacheEntry(
+    val anchorMessageId: Long? = null,
+    val anchorOffsetPx: Int = 0,
+    val atBottom: Boolean = true
+)

domain/src/main/java/org/monogram/domain/repository/CacheProvider.kt

@@ -3,6 +3,7 @@ package org.monogram.domain.repository
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.StateFlow
 import org.monogram.domain.models.AttachMenuBotModel
+import org.monogram.domain.models.ChatViewportCacheEntry
 import org.monogram.domain.models.FolderModel
 import org.monogram.domain.models.GifModel
 import org.monogram.domain.models.RecentEmojiModel
@@ -34,6 +35,9 @@ interface CacheProvider {
     fun saveChatScrollPosition(chatId: Long, messageId: Long)
     fun getChatScrollPosition(chatId: Long): Long
 
+    fun saveChatViewport(chatId: Long, threadId: Long?, viewport: ChatViewportCacheEntry)
+    fun getChatViewport(chatId: Long, threadId: Long?): ChatViewportCacheEntry?
+
     fun setSavedGifs(gifs: List<GifModel>)
 
     fun setInstalledStickerSets(sets: List<StickerSetModel>)

presentation/src/main/java/org/monogram/presentation/core/util/CachePreferences.kt

@@ -6,6 +6,7 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.serialization.json.Json
 import org.monogram.domain.models.AttachMenuBotModel
+import org.monogram.domain.models.ChatViewportCacheEntry
 import org.monogram.domain.models.FolderModel
 import org.monogram.domain.models.GifModel
 import org.monogram.domain.models.RecentEmojiModel
@@ -102,6 +103,33 @@ class CachePreferences(private val context: Context) : CacheProvider {
         return prefs.getLong("chat_scroll_$chatId", 0L)
     }
 
+    override fun saveChatViewport(chatId: Long, threadId: Long?, viewport: ChatViewportCacheEntry) {
+        prefs.edit()
+            .putString(chatViewportKey(chatId, threadId), Json.encodeToString(viewport))
+            .apply()
+    }
+
+    override fun getChatViewport(chatId: Long, threadId: Long?): ChatViewportCacheEntry? {
+        val directJson = prefs.getString(chatViewportKey(chatId, threadId), null)
+        if (!directJson.isNullOrBlank()) {
+            return try {
+                Json.decodeFromString<ChatViewportCacheEntry>(directJson)
+            } catch (_: Exception) {
+                null
+            }
+        }
+
+        if (threadId != null) return null
+        if (!prefs.contains("chat_scroll_$chatId")) return null
+
+        val legacy = prefs.getLong("chat_scroll_$chatId", 0L)
+        return if (legacy == 0L) {
+            ChatViewportCacheEntry(atBottom = true)
+        } else {
+            ChatViewportCacheEntry(anchorMessageId = legacy, anchorOffsetPx = 0, atBottom = false)
+        }
+    }
+
     override fun setSavedGifs(gifs: List<GifModel>) {
         prefs.edit().putString(KEY_SAVED_GIFS, Json.encodeToString(gifs)).apply()
         _savedGifs.value = gifs
@@ -138,5 +166,9 @@ class CachePreferences(private val context: Context) : CacheProvider {
 
     companion object {
         private const val KEY_SAVED_GIFS = "saved_gifs"
+
+        private fun chatViewportKey(chatId: Long, threadId: Long?): String {
+            return "chat_viewport_${chatId}_${threadId ?: 0L}"
+        }
     }
 }

presentation/src/main/java/org/monogram/presentation/features/chats/currentChat/ChatComponent.kt

@@ -3,7 +3,22 @@ package org.monogram.presentation.features.chats.currentChat
 import androidx.compose.runtime.Stable
 import androidx.compose.ui.platform.Clipboard
 import kotlinx.coroutines.flow.StateFlow
-import org.monogram.domain.models.*
+import org.monogram.domain.models.AttachMenuBotModel
+import org.monogram.domain.models.BotCommandModel
+import org.monogram.domain.models.BotMenuButtonModel
+import org.monogram.domain.models.ChatPermissionsModel
+import org.monogram.domain.models.ChatViewportCacheEntry
+import org.monogram.domain.models.GifModel
+import org.monogram.domain.models.InlineKeyboardButtonModel
+import org.monogram.domain.models.KeyboardButtonModel
+import org.monogram.domain.models.MessageEntity
+import org.monogram.domain.models.MessageModel
+import org.monogram.domain.models.MessageSendOptions
+import org.monogram.domain.models.MessageViewerModel
+import org.monogram.domain.models.StickerSetModel
+import org.monogram.domain.models.TopicModel
+import org.monogram.domain.models.UserModel
+import org.monogram.domain.models.WallpaperModel
 import org.monogram.domain.repository.InlineBotResultsModel
 import org.monogram.domain.repository.MessageRepository
 import org.monogram.domain.repository.StickerRepository
@@ -80,11 +95,13 @@ interface ChatComponent {
     fun onShowAllPinnedMessages()
     fun onDismissPinnedMessages()
     fun onScrollToMessageConsumed()
+    fun onScrollCommandConsumed()
     fun onScrollToBottom()
     fun onDownloadFile(fileId: Int)
     fun onDownloadHighRes(messageId: Long)
     fun onCancelDownloadFile(fileId: Int)
     fun updateScrollPosition(messageId: Long)
+    fun updateViewport(viewport: ChatViewportCacheEntry)
     fun onBottomReached(isAtBottom: Boolean)
     fun onHighlightConsumed()
     fun onTyping()
@@ -222,10 +239,12 @@ interface ChatComponent {
         val pinnedMessageCount: Int = 0,
         val pinnedMessageIndex: Int = 0,
         val scrollToMessageId: Long? = null,
+        val pendingScrollCommand: ChatScrollCommand? = null,
         val highlightedMessageId: Long? = null,
         val isAtBottom: Boolean = true,
         val currentScrollMessageId: Long = 0L,
         val lastScrollPosition: Long = 0L,
+        val lastSavedViewport: ChatViewportCacheEntry? = null,
         val isLatestLoaded: Boolean = true,
         val isOldestLoaded: Boolean = false,
         val fontSize: Float = 16f,