feat: paginate, sync, and display branched sessions (#563)

* mobile: 以 Desktop Sessions 作为聊天历史源

* mobile: 修复快速连接崩溃与无标题会话隐藏

* mobile: 对齐 Desktop 标题并恢复完整历史

* mobile: 分离 Desktop 存储 ID 与运行 Session ID

* mobile: 将新对话持久化为 Desktop Session

* mobile: 渲染 Desktop 本地媒体

* feat: 分页加载并同步当前会话

* fix: 显示分支会话名称与层级

* fix: align PR with upstream app contract

* fix: preserve upstream session RPC lifecycle

app/src/main/java/com/m57/hermescontrol/data/model/SessionListResponse.kt

@@ -19,6 +19,8 @@ data class SessionInfo(
     val preview: String? = null,
     val started_at: Double? = null,
     val source: String? = null,
+    val parent_session_id: String? = null,
+    val display_name: String? = null,
 )
 
 @Serializable

app/src/main/java/com/m57/hermescontrol/data/model/SessionTreeItem.kt

@@ -0,0 +1,51 @@
+package com.m57.hermescontrol.data.model
+
+data class SessionTreeItem(
+    val session: SessionInfo,
+    val depth: Int,
+    val branchStem: String?,
+    val displayTitle: String,
+)
+
+fun flattenSessionTree(sessions: List<SessionInfo>): List<SessionTreeItem> {
+    val ids = sessions.mapTo(mutableSetOf()) { it.id }
+    val children = sessions.groupBy { it.parent_session_id?.takeIf(ids::contains) }
+    val result = mutableListOf<SessionTreeItem>()
+    val visited = mutableSetOf<String>()
+
+    fun append(
+        session: SessionInfo,
+        depth: Int,
+        branchStem: String?,
+        siblingIndex: Int,
+    ) {
+        if (!visited.add(session.id)) return
+        val isBranch = session.parent_session_id?.takeIf(ids::contains) != null
+        val title =
+            session.title?.takeIf(String::isNotBlank)
+                ?: session.display_name?.takeIf(String::isNotBlank)
+                ?: if (isBranch) {
+                    "branch ${siblingIndex + 1}"
+                } else {
+                    session.preview?.takeIf(String::isNotBlank)?.take(80) ?: "Untitled"
+                }
+        result += SessionTreeItem(session, depth, branchStem, title)
+        val descendants = children[session.id].orEmpty()
+        descendants.forEachIndexed { index, child ->
+            append(
+                session = child,
+                depth = depth + 1,
+                branchStem = if (index == descendants.lastIndex) "└─" else "├─",
+                siblingIndex = index,
+            )
+        }
+    }
+
+    children[null].orEmpty().forEachIndexed { index, root ->
+        append(root, depth = 0, branchStem = null, siblingIndex = index)
+    }
+    sessions.filterNot { it.id in visited }.forEachIndexed { index, orphan ->
+        append(orphan, depth = 0, branchStem = null, siblingIndex = index)
+    }
+    return result
+}

app/src/main/java/com/m57/hermescontrol/data/remote/HermesApiService.kt

@@ -131,6 +131,8 @@ interface HermesApiService {
         // Preserve slashes in session IDs — backend generates IDs containing '/' characters (issue #468).
         // Contract: The server-generated sessionId must only contain URL-safe characters (no ?, #, or spaces).
         @Path("id", encoded = true) sessionId: String,
+        @Query("limit") limit: Int? = null,
+        @Query("offset") offset: Int = 0,
     ): Response<SessionMessagesResponse>
 
     @GET("api/sessions/stats")

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatScreen.kt

@@ -95,6 +95,7 @@ import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
+import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
@@ -130,12 +131,16 @@ import com.m57.hermescontrol.ui.common.EmptyState
 import com.m57.hermescontrol.ui.common.HermesScaffold
 import com.m57.hermescontrol.ui.common.NavIcon
 import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.collectLatest
+import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.launch
 import java.io.File
 import java.text.SimpleDateFormat
 import java.util.Date
 import java.util.Locale
 
+private const val SESSION_SYNC_INTERVAL_MS = 5_000L
+
 @OptIn(ExperimentalFoundationApi::class)
 @Composable
 fun ChatScreen(
@@ -147,6 +152,27 @@ fun ChatScreen(
     val state by viewModel.uiState.collectAsStateWithLifecycle()
     val streamingState by viewModel.streamingState.collectAsStateWithLifecycle()
     val listState = rememberLazyListState()
+    var isOlderPagingArmed by remember(state.currentSessionId) { mutableStateOf(false) }
+
+    LaunchedEffect(state.currentSessionId, state.connectionStatus) {
+        while (state.currentSessionId != null && state.connectionStatus == ConnectionStatus.CONNECTED) {
+            delay(SESSION_SYNC_INTERVAL_MS)
+            viewModel.syncCurrentSession()
+        }
+    }
+
+    LaunchedEffect(listState, state.currentSessionId, state.hasOlderMessages, state.isLoadingOlder) {
+        if (!state.hasOlderMessages || state.isLoadingOlder) return@LaunchedEffect
+        snapshotFlow { listState.firstVisibleItemIndex }
+            .distinctUntilChanged()
+            .collectLatest { firstVisibleIndex ->
+                if (firstVisibleIndex > 2) {
+                    isOlderPagingArmed = true
+                } else if (isOlderPagingArmed) {
+                    viewModel.loadOlderMessages()
+                }
+            }
+    }
     val showScrollToBottom by remember {
         derivedStateOf {
             state.messages.isNotEmpty() && listState.canScrollForward
@@ -395,6 +421,7 @@ fun ChatScreen(
                     typingEffectEnabled = state.typingEffectEnabled,
                     typingEffectDelayMs = state.typingEffectDelayMs,
                     isLoading = state.isLoading,
+                    isLoadingOlder = state.isLoadingOlder,
                     isDark = isDark,
                     listState = listState,
                     lastAnimatedMessageId = lastAnimatedMessageId,
@@ -1664,6 +1691,7 @@ private fun ChatMessageList(
     typingEffectEnabled: Boolean,
     typingEffectDelayMs: Int,
     isLoading: Boolean,
+    isLoadingOlder: Boolean,
     isDark: Boolean,
     listState: LazyListState,
     lastAnimatedMessageId: String?,
@@ -1717,6 +1745,16 @@ private fun ChatMessageList(
             modifier = Modifier.fillMaxWidth().weight(1f),
             contentPadding = PaddingValues(vertical = 8.dp),
         ) {
+            if (isLoadingOlder) {
+                item(key = "loading-older") {
+                    Box(
+                        modifier = Modifier.fillMaxWidth().padding(12.dp),
+                        contentAlignment = Alignment.Center,
+                    ) {
+                        CircularProgressIndicator(modifier = Modifier.size(24.dp))
+                    }
+                }
+            }
             itemsIndexed(
                 items = messages,
                 key = { _, message -> message.id },

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -10,6 +10,7 @@ import androidx.lifecycle.viewModelScope
 import com.m57.hermescontrol.data.local.AuthManager
 import com.m57.hermescontrol.data.local.HermesDatabase
 import com.m57.hermescontrol.data.model.Attachment
+import com.m57.hermescontrol.data.model.SessionMessage
 import com.m57.hermescontrol.data.remote.ApiClient
 import com.m57.hermescontrol.data.remote.NetworkResult
 import com.m57.hermescontrol.data.remote.OkHttpProvider
@@ -43,6 +44,7 @@ import java.io.ByteArrayOutputStream
 import java.util.concurrent.ConcurrentHashMap
 
 private const val TAG = "ChatViewModel"
+private const val MESSAGE_PAGE_SIZE = 150
 
 data class ChatUiState(
     val messages: List<ChatMessage> = emptyList(),
@@ -54,6 +56,8 @@ data class ChatUiState(
     val isThinking: Boolean = false,
     val thinkingText: String = "",
     val isLoading: Boolean = false,
+    val isLoadingOlder: Boolean = false,
+    val hasOlderMessages: Boolean = false,
     /** Standalone streaming message — rendered after the main list. */
     val streamingMessage: ChatMessage? = null,
     val errorMessage: String? = null,
@@ -89,6 +93,8 @@ data class SessionUi(
     val id: String,
     val title: String,
     val messageCount: Int = 0,
+    val parentSessionId: String? = null,
+    val depth: Int = 0,
 )
 
 data class ClarifyUi(
@@ -123,6 +129,14 @@ class ChatViewModel(
     private val _uiState = MutableStateFlow(ChatUiState())
 
     private val _streamingState = MutableStateFlow(StreamingState())
+
+    /** Maps an in-flight RPC id to its method for UI error labeling. */
+    private val idToMethod = ConcurrentHashMap<String, String>()
+
+    /** Runtime TUI session returned by session.resume; Desktop storage keeps the original ID. */
+    private var runtimeSessionId: String? = null
+    private var loadedMessageOffset = 0
+    private var isSyncingMessages = false
     val streamingState: StateFlow<StreamingState> = _streamingState.asStateFlow()
 
     /** Tracks the auto-clear coroutine for reaction animations. */
@@ -279,7 +293,7 @@ class ChatViewModel(
                 _uiState.value,
                 _streamingState.value,
                 event,
-                _uiState.value.currentSessionId,
+                runtimeSessionId ?: _uiState.value.currentSessionId,
             )
 
         // Apply the new state
@@ -418,7 +432,7 @@ class ChatViewModel(
     private fun isCurrentSession(eventSessionId: String?): Boolean {
         // If the event has no session ID, process it (legacy compatibility)
         if (eventSessionId == null) return true
-        return eventSessionId == _uiState.value.currentSessionId
+        return eventSessionId == runtimeSessionId || eventSessionId == _uiState.value.currentSessionId
     }
 
     // ── RPC response handling ────────────────────────────────────────────
@@ -432,10 +446,12 @@ class ChatViewModel(
         when (method) {
             WsMethods.SESSION_CREATE -> {
                 val resultMap = result as? Map<String, Any?> ?: return
-                val sessionId = resultMap["session_id"] as? String ?: return
+                val runtimeId = resultMap["session_id"] as? String ?: return
+                val storageId = resultMap["stored_session_id"] as? String ?: runtimeId
+                runtimeSessionId = runtimeId
                 _uiState.update {
                     it.copy(
-                        currentSessionId = sessionId,
+                        currentSessionId = storageId,
                         isLoading = false,
                         messages = emptyList(),
                         chatTitle = "Hermes",
@@ -444,7 +460,7 @@ class ChatViewModel(
                 // Mirror the active session id app-wide so session-scoped
                 // drawer screens (e.g. Processes, issue #532) can issue
                 // session-scoped RPCs. See ActiveSessionHolder.
-                ActiveSessionHolder.set(sessionId)
+                ActiveSessionHolder.set(runtimeId)
                 _streamingState.update { StreamingState() }
                 addSystemMessage("Session created", persist = true)
                 loadSessions()
@@ -472,8 +488,9 @@ class ChatViewModel(
 
             WsMethods.SESSION_RESUME -> {
                 val resultMap = result as? Map<String, Any?>
+                runtimeSessionId = resultMap?.get("session_id") as? String
                 val sessionId =
-                    (resultMap?.get("session_id") as? String)
+                    (resultMap?.get("resumed") as? String)
                         ?: _uiState.value.currentSessionId
 
                 // B8 (Jun 20 2026, kanban t_session_resume): do NOT reload
@@ -487,8 +504,8 @@ class ChatViewModel(
                         currentSessionId = sessionId,
                     )
                 }
-                // Mirror the active session id app-wide (issue #532).
+                // Mirror the active runtime session id app-wide (issue #532).
-                ActiveSessionHolder.set(sessionId)
+                ActiveSessionHolder.set(runtimeSessionId ?: sessionId)
                 addSystemMessage("Session resumed")
             }
 
@@ -599,7 +616,8 @@ class ChatViewModel(
      */
     fun sendMessage(text: String) {
         if (text.isBlank() && _uiState.value.pendingAttachments.isEmpty()) return
-        val sessionId = _uiState.value.currentSessionId ?: return
+        val storageSessionId = _uiState.value.currentSessionId ?: return
+        val agentSessionId = runtimeSessionId ?: return
 
         val trimmed = text.trim()
         if (trimmed.startsWith("/", ignoreCase = true)) {
@@ -626,9 +644,9 @@ class ChatViewModel(
             )
         }
 
-        // Persist to Room
+        // Persist under the original Desktop session ID.
         viewModelScope.launch(Dispatchers.IO) {
-            repo.persistMessage(userMessage, sessionId)
+            repo.persistMessage(userMessage, storageSessionId)
         }
 
         // Upload attachments then submit prompt
@@ -689,7 +707,7 @@ class ChatViewModel(
                 }
 
             wsClient.sendMessage(
-                sessionId,
+                agentSessionId,
                 fullText,
                 onSent = { id -> trackRequest(id, WsMethods.PROMPT_SUBMIT) },
             )
@@ -779,7 +797,7 @@ class ChatViewModel(
     }
 
     private fun dispatchViaRpc(command: String) {
-        val sessionId = _uiState.value.currentSessionId
+        val sessionId = runtimeSessionId
         if (sessionId == null) {
             addAssistantMessage("No active session. Use `/new` to create one.")
             return
@@ -803,7 +821,7 @@ class ChatViewModel(
      */
     private fun submitPrompt(text: String) {
         if (text.isBlank()) return
-        val sessionId = _uiState.value.currentSessionId ?: return
+        val sessionId = runtimeSessionId ?: return
         _uiState.update { it.copy(isAgentTyping = true) }
         viewModelScope.launch(Dispatchers.IO) {
             wsClient.sendMessage(
@@ -830,7 +848,7 @@ class ChatViewModel(
     // ── Session management ───────────────────────────────────────────────
 
     fun interruptSession() {
-        val sessionId = _uiState.value.currentSessionId ?: return
+        val sessionId = runtimeSessionId ?: return
         viewModelScope.launch(Dispatchers.IO) {
             wsClient.send(
                 WsMethods.SESSION_INTERRUPT,
@@ -853,6 +871,7 @@ class ChatViewModel(
         viewModelScope.launch(Dispatchers.IO) {
             wsClient.send(
                 WsMethods.SESSION_CREATE,
+                params = mapOf("source" to "desktop"),
                 onSent = { id -> trackRequest(id, WsMethods.SESSION_CREATE) },
             )
         }
@@ -878,15 +897,7 @@ class ChatViewModel(
 
     fun refreshCurrentSession() {
         val sessionId = _uiState.value.currentSessionId ?: return
-        viewModelScope.launch {
+        loadSessionMessages(sessionId)
-            loadCachedMessages(sessionId).join()
-            // Skip the REST call if we already have messages — the WebSocket keeps
-            // the UI current. The REST endpoint can 404 on tab switch-back when the
-            // WS session ID doesn't round-trip through the resolver (issue #366),
-            // showing a misleading error banner while the connection is fine.
-            if (_uiState.value.messages.isNotEmpty()) return@launch
-            loadSessionMessages(sessionId)
-        }
     }
 
     fun refreshSettings() {
@@ -911,12 +922,16 @@ class ChatViewModel(
     fun switchSession(sessionId: String) {
         if (sessionId == _uiState.value.currentSessionId) return
 
-        // Reset streaming state
+        // Reset streaming and pagination state before resuming the Desktop session.
+        runtimeSessionId = null
+        loadedMessageOffset = 0
         streamingController.resetStreaming()
         _uiState.update {
             val title = it.sessions.find { s -> s.id == sessionId }?.title ?: "Hermes"
             it.copy(
                 isLoading = true,
+                isLoadingOlder = false,
+                hasOlderMessages = false,
                 currentSessionId = sessionId,
                 messages = emptyList(),
                 chatTitle = title,
@@ -928,9 +943,7 @@ class ChatViewModel(
         ActiveSessionHolder.set(sessionId)
         _streamingState.update { StreamingState() }
         viewModelScope.launch {
-            // Step 1: Load cached messages first — instant display
+            // Resume the selected desktop session, then load its complete transcript.
-            loadCachedMessages(sessionId).join()
-            // Step 2: Resume session on server
             launch(Dispatchers.IO) {
                 wsClient.send(
                     WsMethods.SESSION_RESUME,
@@ -938,9 +951,7 @@ class ChatViewModel(
                     onSent = { id -> trackRequest(id, WsMethods.SESSION_RESUME) },
                 )
             }
-            // Step 3: Load fresh messages from REST and merge
             loadSessionMessages(sessionId)
-            // Step 4: Refresh session list to get latest titles
             loadSessions()
         }
     }
@@ -960,62 +971,33 @@ class ChatViewModel(
 
     private fun loadSessionMessages(sessionId: String) {
         viewModelScope.launch {
-            val result =
+            val messageCount = fetchServerMessageCount(sessionId)
-                withContext(Dispatchers.IO) {
+            val offset = (messageCount - MESSAGE_PAGE_SIZE).coerceAtLeast(0)
-                    safeApiCall { ApiClient.hermesApi.getSessionMessages(sessionId) }
+            val result = fetchMessagePage(sessionId, offset, MESSAGE_PAGE_SIZE)
-                }
             when (result) {
                 is NetworkResult.Success -> {
-                    val messagesList = result.data.messages.orEmpty()
+                    val chatMessages = mapServerMessages(sessionId, result.data.messages.orEmpty(), offset)
-                    val chatMessages =
+                    loadedMessageOffset = offset
-                        messagesList.mapIndexed { index, msg ->
-                            val role =
-                                when (msg.role?.lowercase()) {
-                                    "user" -> MessageRole.USER
-                                    "system" -> MessageRole.SYSTEM
-                                    "tool" -> MessageRole.TOOL
-                                    else -> MessageRole.ASSISTANT
-                                }
-                            // Use stable IDs based on session + index to prevent
-                            // Room duplicates when re-loading the same session.
-                            val stableId = "rest-$sessionId-$index"
-                            // Preserve original timestamp from the API when available
-                            val ts = msg.timestampText?.toLongOrNull() ?: System.currentTimeMillis()
-                            ChatMessage(
-                                id = stableId,
-                                role = role,
-                                content = msg.content.orEmpty(),
-                                timestamp = ts,
-                                isStreaming = false,
-                            )
-                        }
-                    // Persist loaded messages to Room for offline access
                     withContext(Dispatchers.IO) {
                         repo.persistMessages(chatMessages, sessionId)
                     }
                     _uiState.update { state ->
-                        // Only update if still on the same session
                         if (state.currentSessionId != sessionId) return@update state
-
-                        // Merge: keep any user messages sent between cache load
-                        // and REST response (they won't be in the REST response
-                        // yet), plus preserve any active streaming message.
-                        val existingIds = chatMessages.mapTo(HashSet(chatMessages.size)) { it.id }
-                        val localOnly = state.messages.filter { it.id !in existingIds }
                         state.copy(
-                            messages = chatMessages + localOnly,
+                            messages = chatMessages,
                             isLoading = false,
+                            hasOlderMessages = offset > 0,
+                            isLoadingOlder = false,
                         )
                     }
                 }
 
                 is NetworkResult.Failure -> {
-                    // Don't overwrite messages on REST failure — cached messages
-                    // are still valid.
                     _uiState.update {
                         if (it.currentSessionId != sessionId) return@update it
                         it.copy(
                             isLoading = false,
+                            isLoadingOlder = false,
                             errorMessage = "Failed to load messages: ${result.error.message}",
                         )
                     }
@@ -1024,6 +1006,170 @@ class ChatViewModel(
         }
     }
 
+    fun loadOlderMessages() {
+        val state = _uiState.value
+        val sessionId = state.currentSessionId ?: return
+        if (!state.hasOlderMessages || state.isLoadingOlder || loadedMessageOffset <= 0) return
+        val oldOffset = loadedMessageOffset
+        val newOffset = (oldOffset - MESSAGE_PAGE_SIZE).coerceAtLeast(0)
+        val limit = oldOffset - newOffset
+        _uiState.update { it.copy(isLoadingOlder = true) }
+        viewModelScope.launch {
+            when (val result = fetchMessagePage(sessionId, newOffset, limit)) {
+                is NetworkResult.Success -> {
+                    val older = mapServerMessages(sessionId, result.data.messages.orEmpty(), newOffset)
+                    loadedMessageOffset = newOffset
+                    withContext(Dispatchers.IO) { repo.persistMessages(older, sessionId) }
+                    _uiState.update { current ->
+                        if (current.currentSessionId != sessionId) return@update current
+                        current.copy(
+                            messages = (older + current.messages).distinctBy { it.id },
+                            isLoadingOlder = false,
+                            hasOlderMessages = newOffset > 0,
+                        )
+                    }
+                }
+
+                is NetworkResult.Failure -> {
+                    _uiState.update { it.copy(isLoadingOlder = false) }
+                }
+            }
+        }
+    }
+
+    fun syncCurrentSession() {
+        val state = _uiState.value
+        val sessionId = state.currentSessionId ?: return
+        if (isSyncingMessages || state.isLoading || state.isLoadingOlder || state.isAgentTyping ||
+            _streamingState.value.streamingMessage != null
+        ) {
+            return
+        }
+        val nextOffset =
+            state.messages
+                .mapNotNull { serverMessageIndex(it.id, sessionId) }
+                .maxOrNull()
+                ?.plus(1)
+                ?: loadedMessageOffset
+        isSyncingMessages = true
+        viewModelScope.launch {
+            try {
+                when (val result = fetchMessagePage(sessionId, nextOffset, MESSAGE_PAGE_SIZE)) {
+                    is NetworkResult.Success -> {
+                        val incoming = mapServerMessages(sessionId, result.data.messages.orEmpty(), nextOffset)
+                        if (incoming.isEmpty()) return@launch
+                        withContext(Dispatchers.IO) { repo.persistMessages(incoming, sessionId) }
+                        _uiState.update { current ->
+                            if (current.currentSessionId != sessionId) return@update current
+                            val unmatched = incoming.map { it.role to it.content }.toMutableList()
+                            val retained =
+                                current.messages.filter { existing ->
+                                    if (serverMessageIndex(existing.id, sessionId) != null) {
+                                        true
+                                    } else {
+                                        val duplicate =
+                                            unmatched.indexOfFirst { (role, content) ->
+                                                role == existing.role && content == existing.content
+                                            }
+                                        if (duplicate >= 0) unmatched.removeAt(duplicate)
+                                        duplicate < 0
+                                    }
+                                }
+                            val merged = (retained + incoming).distinctBy { it.id }
+                            if (sameMessages(current.messages, merged)) current else current.copy(messages = merged)
+                        }
+                    }
+
+                    is NetworkResult.Failure -> Unit
+                }
+            } finally {
+                isSyncingMessages = false
+            }
+        }
+    }
+
+    private suspend fun fetchServerMessageCount(sessionId: String): Int {
+        val known = _uiState.value.sessions.find { it.id == sessionId }?.messageCount
+        if (known != null) return known
+        val result =
+            withContext(Dispatchers.IO) {
+                safeApiCall { ApiClient.hermesApi.getSessions(limit = 500, offset = 0, order = "recent") }
+            }
+        if (result is NetworkResult.Success) {
+            val sessions = result.data.sessions.orEmpty()
+            val count = sessions.find { it.id == sessionId }?.message_count
+            if (count != null) {
+                _uiState.update { current ->
+                    current.copy(
+                        sessions =
+                            current.sessions.map {
+                                if (it.id == sessionId) {
+                                    it.copy(
+                                        messageCount = count,
+                                    )
+                                } else {
+                                    it
+                                }
+                            },
+                    )
+                }
+                return count
+            }
+        }
+        return known ?: _uiState.value.messages.size
+    }
+
+    private suspend fun fetchMessagePage(
+        sessionId: String,
+        offset: Int,
+        limit: Int,
+    ) = withContext(Dispatchers.IO) {
+        safeApiCall { ApiClient.hermesApi.getSessionMessages(sessionId, limit = limit, offset = offset) }
+    }
+
+    private fun mapServerMessages(
+        sessionId: String,
+        messages: List<SessionMessage>,
+        offset: Int,
+    ): List<ChatMessage> =
+        messages.mapIndexed { index, msg ->
+            val role =
+                when (msg.role?.lowercase()) {
+                    "user" -> MessageRole.USER
+                    "system" -> MessageRole.SYSTEM
+                    "tool" -> MessageRole.TOOL
+                    else -> MessageRole.ASSISTANT
+                }
+            val globalIndex = offset + index
+            val timestamp =
+                msg.timestampText
+                    ?.toDoubleOrNull()
+                    ?.times(1000)
+                    ?.toLong()
+                    ?: System.currentTimeMillis()
+            ChatMessage(
+                id = "rest-$sessionId-$globalIndex",
+                role = role,
+                content = msg.content.orEmpty(),
+                timestamp = timestamp,
+                isStreaming = false,
+            )
+        }
+
+    private fun serverMessageIndex(
+        id: String,
+        sessionId: String,
+    ): Int? = id.removePrefix("rest-$sessionId-").takeIf { it != id }?.toIntOrNull()
+
+    private fun sameMessages(
+        left: List<ChatMessage>,
+        right: List<ChatMessage>,
+    ): Boolean =
+        left.size == right.size &&
+            left.zip(right).all { (a, b) ->
+                a.id == b.id && a.role == b.role && a.content == b.content
+            }
+
     // ── UI actions ───────────────────────────────────────────────────────
 
     fun toggleSessionPicker() {
@@ -1363,9 +1509,6 @@ class ChatViewModel(
 
     // ── Pending request tracking ─────────────────────────────────────────
 
-    /** Maps an in-flight RPC id → its method, purely for UI error labeling. The deferred/timeout lives in [HermesWsClient.request] (issue #526). */
-    private val idToMethod = ConcurrentHashMap<String, String>()
-
     private fun trackRequest(
         id: String,
         method: String,

app/src/main/java/com/m57/hermescontrol/ui/sessions/SessionsScreen.kt

@@ -76,6 +76,8 @@ import androidx.lifecycle.viewmodel.compose.viewModel
 import com.m57.hermescontrol.ChatScreen
 import com.m57.hermescontrol.NavigationController
 import com.m57.hermescontrol.R
+import com.m57.hermescontrol.data.model.SessionInfo
+import com.m57.hermescontrol.data.model.flattenSessionTree
 import com.m57.hermescontrol.theme.LocalHermesStatusColors
 import com.m57.hermescontrol.theme.LocalSpacing
 import com.m57.hermescontrol.ui.common.EmptyState
@@ -170,11 +172,17 @@ fun SessionsScreen(
     var query by remember { mutableStateOf("") }
     var pruneDays by remember { mutableStateOf("7") }
 
+    val sessionTree = remember(state.sessions) { flattenSessionTree(state.sessions) }
     val filteredSessions =
-        remember(query, state.sessions) {
+        remember(query, sessionTree) {
-            state.sessions.filter { session ->
+            if (query.isBlank()) {
-                session.title?.contains(query, ignoreCase = true) == true ||
+                sessionTree
-                    session.status?.contains(query, ignoreCase = true) == true
+            } else {
+                sessionTree.filter { item ->
+                    item.displayTitle.contains(query, ignoreCase = true) ||
+                        item.session.preview?.contains(query, ignoreCase = true) == true ||
+                        item.session.status?.contains(query, ignoreCase = true) == true
+                }
             }
         }
 
@@ -430,9 +438,13 @@ fun SessionsScreen(
                         contentPadding = listContentPadding,
                         verticalArrangement = listItemSpacing,
                     ) {
-                        items(filteredSessions, key = { it.id }) { session ->
+                        items(filteredSessions, key = { it.session.id }) { item ->
+                            val session = item.session
                             SessionCard(
                                 session = session,
+                                displayTitle = item.displayTitle,
+                                depth = item.depth,
+                                branchStem = item.branchStem,
                                 query = query,
                                 isSelecting = state.isSelecting,
                                 isSelected = session.id in state.selectedIds,
@@ -589,7 +601,10 @@ fun SessionsScreen(
 @OptIn(ExperimentalFoundationApi::class)
 @Composable
 private fun SessionCard(
-    session: com.m57.hermescontrol.data.model.SessionInfo,
+    session: SessionInfo,
+    displayTitle: String,
+    depth: Int,
+    branchStem: String?,
     query: String,
     isSelecting: Boolean,
     isSelected: Boolean,
@@ -603,7 +618,6 @@ private fun SessionCard(
 ) {
     val spacing = LocalSpacing.current
     val statusColors = LocalHermesStatusColors.current
-    val displayTitle = session.title?.takeIf { it.isNotBlank() } ?: stringResource(R.string.history_untitled)
     val isActive = session.status?.lowercase() == "active" || session.status?.lowercase() == "streaming"
     val srcIcon = sourceIcon(session.source)
 
@@ -611,6 +625,7 @@ private fun SessionCard(
         modifier =
             Modifier
                 .fillMaxWidth()
+                .padding(start = (depth * 16).dp)
                 .testTag("session_card_${session.id}")
                 .combinedClickable(
                     onClick = onCardClick,
@@ -643,6 +658,16 @@ private fun SessionCard(
                 Spacer(modifier = Modifier.width(spacing.sm))
             }
 
+            // Branch tree stem
+            if (branchStem != null && !isSelecting) {
+                Text(
+                    text = branchStem,
+                    style = MaterialTheme.typography.labelLarge,
+                    color = MaterialTheme.colorScheme.outline,
+                )
+                Spacer(modifier = Modifier.width(spacing.sm))
+            }
+
             // Source icon
             if (srcIcon != null && !isSelecting) {
                 Icon(

app/src/test/java/com/m57/hermescontrol/data/model/SessionTreeTest.kt

@@ -0,0 +1,45 @@
+package com.m57.hermescontrol.data.model
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class SessionTreeTest {
+    @Test
+    fun nestsBranchesAndUsesDesktopFallbackNames() {
+        val sessions =
+            listOf(
+                SessionInfo(id = "unrelated", title = "Recent root"),
+                SessionInfo(id = "branch-b", parent_session_id = "parent"),
+                SessionInfo(id = "parent", title = "Original"),
+                SessionInfo(id = "branch-a", parent_session_id = "parent", preview = "copied prompt"),
+                SessionInfo(id = "nested", parent_session_id = "branch-a", title = "Named nested branch"),
+            )
+
+        val tree = flattenSessionTree(sessions)
+
+        assertEquals(listOf("unrelated", "parent", "branch-b", "branch-a", "nested"), tree.map { it.session.id })
+        assertEquals(listOf(0, 0, 1, 1, 2), tree.map { it.depth })
+        assertEquals(
+            listOf("Recent root", "Original", "branch 1", "branch 2", "Named nested branch"),
+            tree.map {
+                it.displayTitle
+            },
+        )
+        assertEquals(listOf(null, null, "├─", "└─", "└─"), tree.map { it.branchStem })
+    }
+
+    @Test
+    fun keepsMissingParentsAndCyclesVisible() {
+        val sessions =
+            listOf(
+                SessionInfo(id = "orphan", parent_session_id = "missing", preview = "orphan preview"),
+                SessionInfo(id = "a", parent_session_id = "b"),
+                SessionInfo(id = "b", parent_session_id = "a"),
+            )
+
+        val tree = flattenSessionTree(sessions)
+
+        assertEquals(setOf("orphan", "a", "b"), tree.map { it.session.id }.toSet())
+        assertEquals("orphan preview", tree.first { it.session.id == "orphan" }.displayTitle)
+    }
+}

app/src/test/java/com/m57/hermescontrol/data/remote/HermesApiServiceMockWebServerTest.kt

@@ -141,7 +141,8 @@ class HermesApiServiceMockWebServerTest {
                                     "created_at": "2026-06-20T14:30:00Z",
                                     "message_count": 7,
                                     "status": "idle",
-                                    "source": "web"
+                                    "source": "web",
+                                    "parent_session_id": "abc-123"
                                 }
                             ],
                             "total": 2,
@@ -173,6 +174,7 @@ class HermesApiServiceMockWebServerTest {
             assertEquals(7, second.message_count)
             assertEquals("idle", second.status)
             assertEquals("web", second.source)
+            assertEquals("abc-123", second.parent_session_id)
         }
 
     @Test
@@ -254,6 +256,24 @@ class HermesApiServiceMockWebServerTest {
             assertEquals("tool_execution", messages[2].type)
         }
 
+    @Test
+    fun getSessionMessages_sendsPaginationQuery() =
+        runBlocking {
+            mockServer.enqueue(
+                MockResponse()
+                    .setResponseCode(200)
+                    .setBody("{\"messages\": []}"),
+            )
+
+            val response = api.getSessionMessages("desktop/session", limit = 150, offset = 300)
+
+            assertTrue(response.isSuccessful)
+            assertEquals(
+                "/api/sessions/desktop/session/messages?limit=150&offset=300",
+                mockServer.takeRequest().path,
+            )
+        }
+
     @Test
     fun getSessionMessages_withNullRole_doesNotCrash() =
         runBlocking {