feat(api): enhance message deletion functionality with activeNodeId management

- Introduced `ActiveNodeStrategy` type to define strategies for updating `activeNodeId` when a message is deleted.
- Updated `DeleteMessageResponse` to include `newActiveNodeId` for tracking changes to the active node after deletion.
- Modified the `DELETE` endpoint to accept `activeNodeStrategy` as a query parameter, allowing for flexible handling of active node updates.
- Enhanced the `delete` method in `MessageService` to implement the new strategies, ensuring consistent behavior during message deletions.

packages/shared/data/api/schemas/messages.ts

@@ -64,6 +64,11 @@ export interface UpdateMessageDto {
   status?: MessageStatus
 }
 
+/**
+ * Strategy for updating activeNodeId when the active message is deleted
+ */
+export type ActiveNodeStrategy = 'parent' | 'clear'
+
 /**
  * Response for delete operation
  */
@@ -72,6 +77,8 @@ export interface DeleteMessageResponse {
   deletedIds: string[]
   /** IDs of reparented children (only when cascade=false) */
   reparentedIds?: string[]
+  /** New activeNodeId for the topic (only if activeNodeId was affected by deletion) */
+  newActiveNodeId?: string | null
 }
 
 // ============================================================================
@@ -168,10 +175,19 @@ export interface MessageSchemas {
       body: UpdateMessageDto
       response: Message
     }
-    /** Delete a message (cascade=true deletes descendants, cascade=false reparents children) */
+    /**
+     * Delete a message
+     * - cascade=true: deletes message and all descendants
+     * - cascade=false: reparents children to grandparent
+     * - activeNodeStrategy='parent' (default): sets activeNodeId to parent if affected
+     * - activeNodeStrategy='clear': sets activeNodeId to null if affected
+     */
     DELETE: {
       params: { id: string }
-      query?: { cascade?: boolean }
+      query?: {
+        cascade?: boolean
+        activeNodeStrategy?: ActiveNodeStrategy
+      }
       response: DeleteMessageResponse
     }
   }

src/main/data/api/handlers/messages.ts

@@ -9,7 +9,12 @@
 
 import { messageService } from '@data/services/MessageService'
 import type { ApiHandler, ApiMethods } from '@shared/data/api/apiTypes'
-import type { BranchMessagesQueryParams, MessageSchemas, TreeQueryParams } from '@shared/data/api/schemas/messages'
+import type {
+  ActiveNodeStrategy,
+  BranchMessagesQueryParams,
+  MessageSchemas,
+  TreeQueryParams
+} from '@shared/data/api/schemas/messages'
 
 /**
  * Handler type for a specific message endpoint
@@ -61,9 +66,10 @@ export const messageHandlers: {
     },
 
     DELETE: async ({ params, query }) => {
-      const q = (query || {}) as { cascade?: boolean }
+      const q = (query || {}) as { cascade?: boolean; activeNodeStrategy?: ActiveNodeStrategy }
       const cascade = q.cascade ?? false
-      return await messageService.delete(params.id, cascade)
+      const activeNodeStrategy = q.activeNodeStrategy ?? 'parent'
+      return await messageService.delete(params.id, cascade, activeNodeStrategy)
     }
   }
 }

src/main/data/db/schemas/topic.ts

@@ -3,7 +3,6 @@ import { index, integer, sqliteTable, text } from 'drizzle-orm/sqlite-core'
 
 import { createUpdateDeleteTimestamps, uuidPrimaryKey } from './columnHelpers'
 import { groupTable } from './group'
-// import { messageTable } from './message'
 
 /**
  * Topic table - stores conversation topics/threads
@@ -25,9 +24,7 @@ export const topicTable = sqliteTable(
     // Topic-specific prompt override
     prompt: text(),
     // Active node ID in the message tree
-    // SET NULL: reset to null when the referenced message is deleted
     activeNodeId: text(),
-    // .references(() => messageTable.id, { onDelete: 'set null' }),
 
     // FK to group table for organization
     // SET NULL: preserve topic when group is deleted

src/main/data/services/MessageService.ts

@@ -13,7 +13,12 @@ import { messageTable } from '@data/db/schemas/message'
 import { topicTable } from '@data/db/schemas/topic'
 import { loggerService } from '@logger'
 import { DataApiErrorFactory } from '@shared/data/api'
-import type { CreateMessageDto, UpdateMessageDto } from '@shared/data/api/schemas/messages'
+import type {
+  ActiveNodeStrategy,
+  CreateMessageDto,
+  DeleteMessageResponse,
+  UpdateMessageDto
+} from '@shared/data/api/schemas/messages'
 import type {
   BranchMessage,
   BranchMessagesResponse,
@@ -431,13 +436,42 @@ export class MessageService {
 
   /**
    * Delete a message (hard delete)
+   *
+   * Supports two modes:
+   * - cascade=true: Delete the message and all its descendants
+   * - cascade=false: Delete only this message, reparent children to grandparent
+   *
+   * When the deleted message(s) include the topic's activeNodeId, it will be
+   * automatically updated based on activeNodeStrategy:
+   * - 'parent' (default): Sets activeNodeId to the deleted message's parent
+   * - 'clear': Sets activeNodeId to null
+   *
+   * All operations are performed within a transaction for consistency.
+   *
+   * @param id - Message ID to delete
+   * @param cascade - If true, delete descendants; if false, reparent children (default: false)
+   * @param activeNodeStrategy - Strategy for updating activeNodeId if affected (default: 'parent')
+   * @returns Deletion result including deletedIds, reparentedIds, and newActiveNodeId
+   * @throws NOT_FOUND if message doesn't exist
+   * @throws INVALID_OPERATION if deleting root without cascade=true
    */
-  async delete(id: string, cascade: boolean = false): Promise<{ deletedIds: string[]; reparentedIds?: string[] }> {
+  async delete(
+    id: string,
+    cascade: boolean = false,
+    activeNodeStrategy: ActiveNodeStrategy = 'parent'
+  ): Promise<DeleteMessageResponse> {
     const db = dbService.getDb()
 
     // Get the message
     const message = await this.getById(id)
 
+    // Get topic to check activeNodeId
+    const [topic] = await db.select().from(topicTable).where(eq(topicTable.id, message.topicId)).limit(1)
+
+    if (!topic) {
+      throw DataApiErrorFactory.notFound('Topic', message.topicId)
+    }
+
     // Check if it's a root message
     const isRoot = message.parentId === null
 
@@ -445,34 +479,76 @@ export class MessageService {
       throw DataApiErrorFactory.invalidOperation('delete root message', 'cascade=true required')
     }
 
+    // Get all descendant IDs before transaction (for cascade delete)
+    let descendantIds: string[] = []
     if (cascade) {
-      // Get all descendants
-      const descendantIds = await this.getDescendantIds(id)
-      const allIds = [id, ...descendantIds]
+      descendantIds = await this.getDescendantIds(id)
+    }
 
-      // Hard delete all
-      await db.delete(messageTable).where(inArray(messageTable.id, allIds))
+    // Use transaction for atomic delete + activeNodeId update
+    return await db.transaction(async (tx) => {
+      let deletedIds: string[]
+      let reparentedIds: string[] | undefined
+      let newActiveNodeId: string | null | undefined
 
-      logger.info('Cascade deleted messages', { rootId: id, count: allIds.length })
+      if (cascade) {
+        deletedIds = [id, ...descendantIds]
 
-      return { deletedIds: allIds }
-    } else {
-      // Reparent children to this message's parent
-      const children = await db.select({ id: messageTable.id }).from(messageTable).where(eq(messageTable.parentId, id))
+        // Check if activeNodeId is affected
+        if (topic.activeNodeId && deletedIds.includes(topic.activeNodeId)) {
+          newActiveNodeId = activeNodeStrategy === 'clear' ? null : message.parentId
+        }
 
-      const childIds = children.map((c) => c.id)
+        // Hard delete all
+        await tx.delete(messageTable).where(inArray(messageTable.id, deletedIds))
 
-      if (childIds.length > 0) {
-        await db.update(messageTable).set({ parentId: message.parentId }).where(inArray(messageTable.id, childIds))
+        logger.info('Cascade deleted messages', { rootId: id, count: deletedIds.length })
+      } else {
+        // Reparent children to this message's parent
+        const children = await tx
+          .select({ id: messageTable.id })
+          .from(messageTable)
+          .where(eq(messageTable.parentId, id))
+
+        reparentedIds = children.map((c) => c.id)
+
+        if (reparentedIds.length > 0) {
+          await tx
+            .update(messageTable)
+            .set({ parentId: message.parentId })
+            .where(inArray(messageTable.id, reparentedIds))
+        }
+
+        deletedIds = [id]
+
+        // Check if activeNodeId is affected
+        if (topic.activeNodeId === id) {
+          newActiveNodeId = activeNodeStrategy === 'clear' ? null : message.parentId
+        }
+
+        // Hard delete this message
+        await tx.delete(messageTable).where(eq(messageTable.id, id))
+
+        logger.info('Deleted message with reparenting', { id, reparentedCount: reparentedIds.length })
       }
 
-      // Hard delete this message
-      await db.delete(messageTable).where(eq(messageTable.id, id))
+      // Update topic.activeNodeId if needed
+      if (newActiveNodeId !== undefined) {
+        await tx.update(topicTable).set({ activeNodeId: newActiveNodeId }).where(eq(topicTable.id, message.topicId))
 
-      logger.info('Deleted message with reparenting', { id, reparentedCount: childIds.length })
+        logger.info('Updated topic activeNodeId after message deletion', {
+          topicId: message.topicId,
+          oldActiveNodeId: topic.activeNodeId,
+          newActiveNodeId
+        })
+      }
 
-      return { deletedIds: [id], reparentedIds: childIds }
-    }
+      return {
+        deletedIds,
+        reparentedIds: reparentedIds?.length ? reparentedIds : undefined,
+        newActiveNodeId
+      }
+    })
   }
 
   /**