feat(chat): Implement session forking functionality

desktop-shared/src/main/kotlin/io/askimo/ui/chat/ChatActions.kt

@@ -26,4 +26,11 @@ interface ChatActions {
     fun retryMessage(messageId: String, enabledServerIds: Set<String> = emptySet())
     fun toggleBookmark(messageId: String)
     fun clearPendingScroll()
+
+    /**
+     * Fork the current session from the given AI message, creating a new independent
+     * session pre-populated with all active messages up to and including [messageId],
+     * then navigate to the new session immediately.
+     */
+    fun forkFromMessage(messageId: String)
 }

desktop-shared/src/main/kotlin/io/askimo/ui/chat/ChatView.kt

@@ -1105,6 +1105,7 @@ fun chatView(
                                         onRetryMessage = { messageId -> actions.retryMessage(messageId, currentEnabledServerIds) },
                                         viewportTopY = viewportBounds?.top,
                                         projectId = project?.id,
+                                        onForkFromMessage = { messageId -> actions.forkFromMessage(messageId) },
                                     )
                                 }
 
@@ -1142,6 +1143,7 @@ fun chatView(
                                         activeToolCalls = activeToolCalls,
                                         bookmarkedMessageIds = bookmarkedMessageIds,
                                         onToggleBookmark = { messageId -> actions.toggleBookmark(messageId) },
+                                        onForkFromMessage = { messageId -> actions.forkFromMessage(messageId) },
                                     )
                                 }
                             }

desktop-shared/src/main/kotlin/io/askimo/ui/chat/ChatViewModel.kt

@@ -1327,4 +1327,32 @@ class ChatViewModel(
     override fun clearPendingScroll() {
         pendingScrollToMessageId = null
     }
+
+    /**
+     * Fork the current session from [messageId], creating a new independent session
+     * pre-populated with all active messages up to and including that message, then
+     * switching to the new session immediately.
+     *
+     * The operation runs on [Dispatchers.IO] and is fire-and-forget from the UI's
+     * perspective — no loading state is shown because forking is fast and non-blocking
+     * to the current conversation.
+     */
+    override fun forkFromMessage(messageId: String) {
+        val sourceSessionId = currentSessionId.value ?: return
+
+        scope.launch {
+            try {
+                val forkedSession = withContext(Dispatchers.IO) {
+                    chatSessionService.forkSession(sourceSessionId, messageId)
+                }
+                // switchToSession updates activeSessionId and resumes the ViewModel
+                // for the new session — runs on the calling (main) dispatcher.
+                sessionManager.switchToSession(forkedSession.id)
+                log.debug("Forked session {} → navigated to {}", sourceSessionId, forkedSession.id)
+            } catch (e: Exception) {
+                log.error("Failed to fork session from message {}", messageId, e)
+                errorMessage = "Failed to fork conversation. Please try again."
+            }
+        }
+    }
 }

desktop-shared/src/main/kotlin/io/askimo/ui/chat/MessageComponents.kt

@@ -30,6 +30,7 @@ import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.text.input.rememberTextFieldState
 import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.CallSplit
 import androidx.compose.material.icons.filled.AttachFile
 import androidx.compose.material.icons.filled.Bookmark
 import androidx.compose.material.icons.filled.BookmarkBorder
@@ -134,6 +135,7 @@ fun messageList(
     activeToolCalls: List<ToolCallInfo> = emptyList(),
     bookmarkedMessageIds: Set<String> = emptySet(),
     onToggleBookmark: ((String) -> Unit)? = null,
+    onForkFromMessage: ((String) -> Unit)? = null,
 ) {
     // Retry confirmation dialog state
     var showRetryConfirmDialog by remember { mutableStateOf(false) }
@@ -227,6 +229,7 @@ fun messageList(
                         toolCalls = if (isLastAiMsg) activeToolCalls else emptyList(),
                         bookmarkedMessageIds = bookmarkedMessageIds,
                         onToggleBookmark = onToggleBookmark,
+                        onForkFromMessage = onForkFromMessage,
                     )
                     isFirstMessage = false
                     messageIndex++
@@ -324,6 +327,7 @@ fun messageBubble(
     toolCalls: List<ToolCallInfo> = emptyList(),
     bookmarkedMessageIds: Set<String> = emptySet(),
     onToggleBookmark: ((String) -> Unit)? = null,
+    onForkFromMessage: ((String) -> Unit)? = null,
 ) {
     Box(
         modifier = Modifier
@@ -362,6 +366,7 @@ fun messageBubble(
                 toolCalls = toolCalls,
                 isBookmarked = message.id != null && message.id in bookmarkedMessageIds,
                 onToggleBookmark = if (message.id != null) onToggleBookmark else null,
+                onForkFromMessage = if (message.id != null) onForkFromMessage else null,
             )
         }
     }
@@ -630,6 +635,7 @@ private fun aiMessageBubble(
     toolCalls: List<ToolCallInfo> = emptyList(),
     isBookmarked: Boolean = false,
     onToggleBookmark: ((String) -> Unit)? = null,
+    onForkFromMessage: ((String) -> Unit)? = null,
 ) {
     val clipboardManager = LocalClipboardManager.current
     var showCopyFeedback by remember { mutableStateOf(false) }
@@ -969,6 +975,24 @@ private fun aiMessageBubble(
                             }
                         }
                     }
+
+                    // Fork session from here
+                    if (onForkFromMessage != null && message.id != null && !isStreaming) {
+                        val msgId = message.id!!
+                        themedTooltip(text = stringResource("message.ai.fork")) {
+                            IconButton(
+                                onClick = { onForkFromMessage.invoke(msgId) },
+                                modifier = Modifier.size(32.dp).pointerHoverIcon(PointerIcon.Hand),
+                            ) {
+                                Icon(
+                                    imageVector = Icons.AutoMirrored.Filled.CallSplit,
+                                    contentDescription = stringResource("message.ai.fork.description"),
+                                    modifier = Modifier.size(16.dp),
+                                    tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                                )
+                            }
+                        }
+                    }
                 }
             }
 

desktop-shared/src/main/kotlin/io/askimo/ui/session/SessionTooltip.kt

@@ -40,7 +40,7 @@ import io.askimo.ui.common.ui.themedRichTooltip
 @Composable
 fun sessionTooltip(
     session: ChatSession,
-    placement: TooltipPlacement = TooltipPlacement.AUTO,
+    placement: TooltipPlacement = TooltipPlacement.RIGHT,
     modifier: Modifier = Modifier,
     content: @Composable () -> Unit,
 ) {

desktop-shared/src/main/kotlin/io/askimo/ui/shell/NavigationSidebar.kt

@@ -117,7 +117,6 @@ interface ProjectsSidebarState {
  *
  * This keeps the sidebar decoupled from module-specific View enums and auth concerns
  */
-@OptIn(ExperimentalFoundationApi::class)
 @Composable
 fun navigationSidebar(
     isExpanded: Boolean,

desktop-shared/src/main/resources/i18n/messages.properties

@@ -840,6 +840,8 @@ message.ai.try.again.confirm.title=Regenerate response?
 message.ai.try.again.confirm.message=This will delete all messages after this point. Do you want to continue?
 message.ai.try.again.confirm.cancel=Cancel
 message.ai.try.again.confirm.confirm=Regenerate
+message.ai.fork=Fork session from here
+message.ai.fork.description=Fork this conversation into a new independent session
 message.ai.export.pdf=Export as PDF
 message.ai.export.pdf.dialog.title=Save AI Response as PDF
 message.bookmark=Bookmark message

desktop-shared/src/main/resources/i18n/messages_de.properties

@@ -816,6 +816,8 @@ message.ai.try.again.confirm.title=Antwort neu generieren?
 message.ai.try.again.confirm.message=Alle Nachrichten nach diesem Punkt werden gelöscht. Möchten Sie fortfahren?
 message.ai.try.again.confirm.cancel=Abbrechen
 message.ai.try.again.confirm.confirm=Neu generieren
+message.ai.fork=Session von hier aus forken
+message.ai.fork.description=Diese Unterhaltung in eine neue, unabhängige Session forken
 message.ai.export.pdf=Als PDF exportieren
 message.ai.export.pdf.dialog.title=KI-Antwort als PDF speichern
 message.edited.indicator=(bearbeitet)

desktop-shared/src/main/resources/i18n/messages_es.properties

@@ -815,6 +815,8 @@ message.ai.try.again.confirm.title=¿Regenerar respuesta?
 message.ai.try.again.confirm.message=Esto eliminará todos los mensajes posteriores a este punto. ¿Desea continuar?
 message.ai.try.again.confirm.cancel=Cancelar
 message.ai.try.again.confirm.confirm=Regenerar
+message.ai.fork=Fork session from here
+message.ai.fork.description=Fork this conversation into a new independent session
 message.ai.export.pdf=Exportar como PDF
 message.ai.export.pdf.dialog.title=Guardar respuesta de IA como PDF
 message.edited.indicator=(editado)

desktop-shared/src/main/resources/i18n/messages_fr.properties

@@ -815,6 +815,8 @@ message.ai.try.again.confirm.title=Régénérer la réponse ?
 message.ai.try.again.confirm.message=Tous les messages après ce point seront supprimés. Voulez-vous continuer ?
 message.ai.try.again.confirm.cancel=Annuler
 message.ai.try.again.confirm.confirm=Régénérer
+message.ai.fork=Hacer fork de la sesión desde aquí
+message.ai.fork.description=Dividir esta conversación en una nueva sesión independiente
 message.ai.export.pdf=Exporter en PDF
 message.ai.export.pdf.dialog.title=Enregistrer la reponse IA en PDF
 message.edited.indicator=(modifié)

desktop-shared/src/main/resources/i18n/messages_ja_JP.properties

@@ -814,6 +814,8 @@ message.ai.try.again.confirm.title=回答を再生成しますか？
 message.ai.try.again.confirm.message=この時点以降のすべてのメッセージが削除されます。続行しますか？
 message.ai.try.again.confirm.cancel=キャンセル
 message.ai.try.again.confirm.confirm=再生成
+message.ai.fork=ここからセッションをフォーク
+message.ai.fork.description=この会話を新しい独立したセッションにフォークする
 message.ai.export.pdf=PDFとしてエクスポート
 message.ai.export.pdf.dialog.title=AIの回答をPDFとして保存
 message.edited.indicator=(編集済み)

desktop-shared/src/main/resources/i18n/messages_ko_KR.properties

@@ -815,6 +815,8 @@ message.ai.try.again.confirm.title=응답을 다시 생성하시겠습니까?
 message.ai.try.again.confirm.message=이 시점 이후의 모든 메시지가 삭제됩니다. 계속하시겠습니까?
 message.ai.try.again.confirm.cancel=취소
 message.ai.try.again.confirm.confirm=다시 생성
+message.ai.fork=여기서 세션 포크(Fork)
+message.ai.fork.description=이 대화를 새로운 독립 세션으로 포크(Fork)합니다
 message.ai.export.pdf=PDF로 내보내기
 message.ai.export.pdf.dialog.title=AI 응답을 PDF로 저장
 message.edited.indicator=(편집됨)

desktop-shared/src/main/resources/i18n/messages_pt_BR.properties

@@ -817,6 +817,8 @@ message.ai.try.again.confirm.title=Regenerar resposta?
 message.ai.try.again.confirm.message=Isso excluirá todas as mensagens após este ponto. Deseja continuar?
 message.ai.try.again.confirm.cancel=Cancelar
 message.ai.try.again.confirm.confirm=Regenerar
+message.ai.fork=Fazer fork da sessão a partir daqui
+message.ai.fork.description=Dividir esta conversa em uma nova sessão independente
 message.ai.export.pdf=Exportar como PDF
 message.ai.export.pdf.dialog.title=Salvar resposta da IA como PDF
 message.edited.indicator=(editado)

desktop-shared/src/main/resources/i18n/messages_vi_VN.properties

@@ -813,6 +813,8 @@ message.ai.try.again.confirm.title=Tạo lại phản hồi?
 message.ai.try.again.confirm.message=Tất cả các tin nhắn sau thời điểm này sẽ bị xóa. Bạn có muốn tiếp tục không?
 message.ai.try.again.confirm.cancel=Hủy
 message.ai.try.again.confirm.confirm=Tạo lại
+message.ai.fork=Fork phiên từ đây
+message.ai.fork.description=Fork cuộc trò chuyện này thành một phiên mới độc lập
 message.ai.export.pdf=Xuất ra PDF
 message.ai.export.pdf.dialog.title=Lưu phản hồi AI dưới dạng PDF
 message.edited.indicator=(đã chỉnh sửa)

desktop-shared/src/main/resources/i18n/messages_zh_CN.properties

@@ -814,6 +814,8 @@ message.ai.try.again.confirm.title=重新生成回复？
 message.ai.try.again.confirm.message=此操作将删除此位置之后的所有消息。是否继续？
 message.ai.try.again.confirm.cancel=取消
 message.ai.try.again.confirm.confirm=重新生成
+message.ai.fork=从此处 Fork 会话
+message.ai.fork.description=将此对话 Fork 为一个新的独立会话
 message.ai.export.pdf=导出为 PDF
 message.ai.export.pdf.dialog.title=将 AI 回复保存为 PDF
 message.edited.indicator=(已编辑)

desktop-shared/src/main/resources/i18n/messages_zh_TW.properties

@@ -814,6 +814,8 @@ message.ai.try.again.confirm.title=重新產生回應？
 message.ai.try.again.confirm.message=此操作將刪除此位置之後的所有訊息。是否要繼續？
 message.ai.try.again.confirm.cancel=取消
 message.ai.try.again.confirm.confirm=重新產生
+message.ai.fork=從此處 Fork 會話
+message.ai.fork.description=將此對話 Fork 為一個新的獨立會話
 message.ai.export.pdf=匯出為 PDF
 message.ai.export.pdf.dialog.title=將 AI 回覆儲存為 PDF
 message.edited.indicator=(已編輯)

shared/src/main/kotlin/io/askimo/core/chat/repository/ChatMessageRepository.kt

@@ -132,6 +132,56 @@ class ChatMessageRepository internal constructor(
         return messageWithInjectedFields
     }
 
+    /**
+     * Bulk-insert a list of messages in a single transaction.
+     * Intended for operations like session forking where all messages must be
+     * written atomically.
+     *
+     * @param messages The messages to insert. Empty IDs are replaced with new UUIDs.
+     * @return The inserted messages with their generated IDs.
+     */
+    fun addMessages(messages: List<ChatMessage>): List<ChatMessage> {
+        if (messages.isEmpty()) return emptyList()
+
+        val messagesWithIds = messages.map { message ->
+            message.copy(id = message.id.ifBlank { UUID.randomUUID().toString() })
+        }
+
+        transaction(database) {
+            messagesWithIds.forEach { msg ->
+                ChatMessagesTable.insert {
+                    it[id] = msg.id
+                    it[ChatMessagesTable.sessionId] = msg.sessionId
+                    it[ChatMessagesTable.role] = msg.role.value
+                    it[ChatMessagesTable.content] = msg.content
+                    it[createdAt] = msg.createdAt
+                    it[ChatMessagesTable.isOutdated] = if (msg.isOutdated) 1 else 0
+                    it[ChatMessagesTable.editParentId] = msg.editParentId
+                    it[ChatMessagesTable.isEdited] = if (msg.isEdited) 1 else 0
+                    it[ChatMessagesTable.isFailed] = if (msg.isFailed) 1 else 0
+                    it[ChatMessagesTable.inputTokens] = msg.inputTokens
+                    it[ChatMessagesTable.outputTokens] = msg.outputTokens
+                    it[ChatMessagesTable.totalTokens] = msg.totalTokens
+                    it[ChatMessagesTable.durationMs] = msg.durationMs
+                }
+
+                if (msg.attachments.isNotEmpty()) {
+                    attachmentRepository.addAttachments(
+                        msg.attachments.map { attachment ->
+                            attachment.copy(
+                                id = attachment.id.ifEmpty { UUID.randomUUID().toString() },
+                                messageId = msg.id,
+                                sessionId = msg.sessionId,
+                            )
+                        },
+                    )
+                }
+            }
+        }
+
+        return messagesWithIds
+    }
+
     fun getMessages(sessionId: String): List<ChatMessage> = transaction(database) {
         val messages = ChatMessagesTable
             .selectAll()

shared/src/main/kotlin/io/askimo/core/chat/service/ChatSessionService.kt

@@ -379,6 +379,82 @@ class ChatSessionService(
         return createdSession
     }
 
+    /**
+     * Fork a session from a specific AI message.
+     *
+     * Creates a new independent session pre-populated with all active (non-outdated)
+     * messages from [sourceSessionId] up to and including [upToMessageId].
+     * The forked session inherits the source session's [ChatSession.directiveId] and
+     * [ChatSession.projectId]. All messages are given fresh IDs; the source session is
+     * left completely untouched.
+     *
+     * @param sourceSessionId The ID of the session to fork from.
+     * @param upToMessageId   The ID of the AI message to fork from (inclusive).
+     * @return The newly created (forked) [ChatSession].
+     * @throws IllegalArgumentException if [sourceSessionId] does not exist or
+     *   [upToMessageId] is not found among its active messages.
+     */
+    fun forkSession(sourceSessionId: String, upToMessageId: String): ChatSession {
+        val sourceSession = sessionRepository.getSession(sourceSessionId)
+            ?: throw IllegalArgumentException("Source session $sourceSessionId not found")
+
+        // Collect active messages up to and including the target message (chronological order).
+        val allMessages = messageRepository.getMessages(sourceSessionId)
+        val activeMessages = allMessages.filter { !it.isOutdated }
+        val targetIndex = activeMessages.indexOfFirst { it.id == upToMessageId }
+        require(targetIndex >= 0) {
+            "Message $upToMessageId not found in active messages of session $sourceSessionId"
+        }
+        val messagesToCopy = activeMessages.subList(0, targetIndex + 1)
+
+        // Create the forked session (no AI title generation — title is already descriptive).
+        val forkedSession = sessionRepository.createSession(
+            ChatSession(
+                id = "",
+                title = "Fork of: ${sourceSession.title}",
+                directiveId = sourceSession.directiveId,
+                projectId = sourceSession.projectId,
+            ),
+        )
+
+        // Bulk-insert all copied messages under the new session ID with fresh UUIDs.
+        val copiedMessages = messagesToCopy.map { msg ->
+            msg.copy(
+                id = "", // auto-UUID in addMessages()
+                sessionId = forkedSession.id,
+                isOutdated = false,
+                isBookmarked = false,
+                editParentId = null,
+            )
+        }
+        messageRepository.addMessages(copiedMessages)
+
+        // Update the session's updatedAt timestamp to reflect the bulk write.
+        sessionRepository.touchSession(forkedSession.id)
+
+        // Warm up a chat client for the new session so it is ready immediately.
+        getOrCreateClientForSession(forkedSession.id)
+
+        eventScope.launch {
+            EventBus.emit(
+                SessionCreatedEvent(
+                    sessionId = forkedSession.id,
+                    projectId = forkedSession.projectId,
+                ),
+            )
+        }
+
+        log.info(
+            "Forked session {} from session {} up to message {} ({} messages copied)",
+            forkedSession.id,
+            sourceSessionId,
+            upToMessageId,
+            copiedMessages.size,
+        )
+
+        return forkedSession
+    }
+
     /**
      * Delete a session and all its related data (messages and summaries).
      * This method coordinates the deletion across multiple repositories.