♻️ refactor: consolidate Claude Code system message handling and streaming logic

- Unify buildClaudeCodeSystemMessage implementation in shared package
- Refactor MessagesService to provide comprehensive message processing API
- Extract streaming logic, error handling, and header preparation into service methods
- Remove duplicate anthropic config from renderer, use shared implementation
- Update ClaudeCodeService to use append mode for custom instructions
- Improve type safety and request validation in message processing

packages/shared/anthropic/index.ts

@@ -12,8 +12,19 @@ import Anthropic from '@anthropic-ai/sdk'
 import { TextBlockParam } from '@anthropic-ai/sdk/resources'
 import { loggerService } from '@logger'
 import { Provider } from '@types'
+import type { ModelMessage } from 'ai'
+
 const logger = loggerService.withContext('anthropic-sdk')
 
+const defaultClaudeCodeSystemPrompt = `You are Claude Code, Anthropic's official CLI for Claude.`
+
+const defaultClaudeCodeSystem: Array<TextBlockParam> = [
+  {
+    type: 'text',
+    text: defaultClaudeCodeSystemPrompt
+  }
+]
+
 /**
  * Creates and configures an Anthropic SDK client based on the provider configuration.
  *
@@ -44,7 +55,11 @@ const logger = loggerService.withContext('anthropic-sdk')
  * const apiKeyClient = getSdkClient(apiKeyProvider);
  * ```
  */
-export function getSdkClient(provider: Provider, oauthToken?: string | null): Anthropic {
+export function getSdkClient(
+  provider: Provider,
+  oauthToken?: string | null,
+  extraHeaders?: Record<string, string | string[]>
+): Anthropic {
   if (provider.authType === 'oauth') {
     if (!oauthToken) {
       throw new Error('OAuth token is not available')
@@ -68,7 +83,8 @@ export function getSdkClient(provider: Provider, oauthToken?: string | null): An
         'x-stainless-os': 'MacOS',
         'x-stainless-arch': 'arm64',
         'x-stainless-runtime': 'node',
-        'x-stainless-runtime-version': 'v22.18.0'
+        'x-stainless-runtime-version': 'v22.18.0',
+        ...extraHeaders
       }
     })
   }
@@ -87,7 +103,8 @@ export function getSdkClient(provider: Provider, oauthToken?: string | null): An
       defaultHeaders: {
         'anthropic-beta': 'output-128k-2025-02-19',
         'APP-Code': 'MLTG2087',
-        ...provider.extra_headers
+        ...provider.extra_headers,
+        ...extraHeaders
       }
     })
   }
@@ -118,53 +135,36 @@ export function getSdkClient(provider: Provider, oauthToken?: string | null): An
  * @param system - Optional user-provided system message (string or TextBlockParam array)
  * @returns Combined system message with Claude Code prompt prepended
  *
- * @example
- * ```typescript
- * // No system message
- * const result1 = buildClaudeCodeSystemMessage();
- * // Returns: "You are Claude Code, Anthropic's official CLI for Claude."
- *
- * // String system message
- * const result2 = buildClaudeCodeSystemMessage("You are a helpful assistant.");
- * // Returns: [
- * //   { type: 'text', text: "You are Claude Code, Anthropic's official CLI for Claude." },
- * //   { type: 'text', text: "You are a helpful assistant." }
- * // ]
- *
- * // Array system message
- * const systemArray = [{ type: 'text', text: 'Custom instructions' }];
- * const result3 = buildClaudeCodeSystemMessage(systemArray);
- * // Returns: Array with Claude Code message prepended
  * ```
  */
-export function buildClaudeCodeSystemMessage(system?: string | Array<TextBlockParam>): string | Array<TextBlockParam> {
-  const defaultClaudeCodeSystem = `You are Claude Code, Anthropic's official CLI for Claude.`
+export function buildClaudeCodeSystemMessage(system?: string | Array<TextBlockParam>): Array<TextBlockParam> {
   if (!system) {
     return defaultClaudeCodeSystem
   }
 
   if (typeof system === 'string') {
-    if (system.trim() === defaultClaudeCodeSystem) {
-      return system
+    if (system.trim() === defaultClaudeCodeSystemPrompt || system.trim() === '') {
+      return defaultClaudeCodeSystem
+    } else {
+      return [...defaultClaudeCodeSystem, { type: 'text', text: system }]
+    }
+  }
+  if (Array.isArray(system)) {
+    const firstSystem = system[0]
+    if (firstSystem.type === 'text' && firstSystem.text.trim() === defaultClaudeCodeSystemPrompt) {
+      return system
+    } else {
+      return [...defaultClaudeCodeSystem, ...system]
     }
-    return [
-      {
-        type: 'text',
-        text: defaultClaudeCodeSystem
-      },
-      {
-        type: 'text',
-        text: system
-      }
-    ]
   }
 
-  if (system[0].text.trim() != defaultClaudeCodeSystem) {
-    system.unshift({
-      type: 'text',
-      text: defaultClaudeCodeSystem
-    })
-  }
-
-  return system
+  return defaultClaudeCodeSystem
+}
+
+export function buildClaudeCodeSystemModelMessage(system?: string | Array<TextBlockParam>): Array<ModelMessage> {
+  const textBlocks = buildClaudeCodeSystemMessage(system)
+  return textBlocks.map((block) => ({
+    role: 'system',
+    content: block.text
+  }))
 }

src/main/apiServer/routes/messages.ts

@@ -1,9 +1,9 @@
 import { MessageCreateParams } from '@anthropic-ai/sdk/resources'
 import { loggerService } from '@logger'
+import { Provider } from '@types'
 import express, { Request, Response } from 'express'
 
-import { Provider } from '../../../renderer/src/types/provider'
-import { MessagesService, messagesService } from '../services/messages'
+import { messagesService } from '../services/messages'
 import { getProviderById, validateModelId } from '../utils'
 
 const logger = loggerService.withContext('ApiServerMessagesRoutes')
@@ -11,7 +11,7 @@ const logger = loggerService.withContext('ApiServerMessagesRoutes')
 const router = express.Router()
 const providerRouter = express.Router({ mergeParams: true })
 
-// Helper functions for shared logic
+// Helper function for basic request validation
 async function validateRequestBody(req: Request): Promise<{ valid: boolean; error?: any }> {
   const request: MessageCreateParams = req.body
 
@@ -31,157 +31,53 @@ async function validateRequestBody(req: Request): Promise<{ valid: boolean; erro
   return { valid: true }
 }
 
-async function handleStreamingResponse(
-  res: Response,
-  request: MessageCreateParams,
-  provider: Provider,
-  messagesService: MessagesService
-): Promise<void> {
-  res.setHeader('Content-Type', 'text/event-stream; charset=utf-8')
-  res.setHeader('Cache-Control', 'no-cache, no-transform')
-  res.setHeader('Connection', 'keep-alive')
-  res.setHeader('X-Accel-Buffering', 'no')
-  res.flushHeaders()
-  const flushableResponse = res as Response & { flush?: () => void }
-  const flushStream = () => {
-    if (typeof flushableResponse.flush !== 'function') {
-      return
-    }
-    try {
-      flushableResponse.flush()
-    } catch (flushError: unknown) {
-      logger.warn('Failed to flush streaming response', {
-        error: flushError
-      })
-    }
-  }
-
-  try {
-    for await (const chunk of messagesService.processStreamingMessage(request, provider)) {
-      res.write(`event: ${chunk.type}\n`)
-      res.write(`data: ${JSON.stringify(chunk)}\n\n`)
-      flushStream()
-    }
-    res.write('data: [DONE]\n\n')
-    flushStream()
-  } catch (streamError: any) {
-    logger.error('Stream error', {
-      error: streamError,
-      provider: provider.id,
-      model: request.model,
-      apiHost: provider.apiHost,
-      anthropicApiHost: provider.anthropicApiHost
-    })
-    res.write(
-      `data: ${JSON.stringify({
-        type: 'error',
-        error: {
-          type: 'api_error',
-          message: 'Stream processing error'
-        }
-      })}\n\n`
-    )
-  } finally {
-    res.end()
-  }
-}
-
-function handleErrorResponse(res: Response, error: any): Response {
-  logger.error('Message processing error', { error })
-
-  let statusCode = 500
-  let errorType = 'api_error'
-  let errorMessage = 'Internal server error'
-
-  const anthropicStatus = typeof error?.status === 'number' ? error.status : undefined
-  const anthropicError = error?.error
-
-  if (anthropicStatus) {
-    statusCode = anthropicStatus
-  }
-
-  if (anthropicError?.type) {
-    errorType = anthropicError.type
-  }
-
-  if (anthropicError?.message) {
-    errorMessage = anthropicError.message
-  } else if (error instanceof Error && error.message) {
-    errorMessage = error.message
-  }
-
-  if (!anthropicStatus && error instanceof Error) {
-    if (error.message.includes('API key') || error.message.includes('authentication')) {
-      statusCode = 401
-      errorType = 'authentication_error'
-    } else if (error.message.includes('rate limit') || error.message.includes('quota')) {
-      statusCode = 429
-      errorType = 'rate_limit_error'
-    } else if (error.message.includes('timeout') || error.message.includes('connection')) {
-      statusCode = 502
-      errorType = 'api_error'
-    } else if (error.message.includes('validation') || error.message.includes('invalid')) {
-      statusCode = 400
-      errorType = 'invalid_request_error'
-    }
-  }
-
-  return res.status(statusCode).json({
-    type: 'error',
-    error: {
-      type: errorType,
-      message: errorMessage,
-      requestId: error?.request_id
-    }
-  })
-}
-
-async function processMessageRequest(
-  req: Request,
-  res: Response,
-  provider: Provider,
+interface HandleMessageProcessingOptions {
+  req: Request
+  res: Response
+  provider: Provider
+  request: MessageCreateParams
   modelId?: string
-): Promise<Response | void> {
+}
+
+async function handleMessageProcessing({
+  req,
+  res,
+  provider,
+  request,
+  modelId
+}: HandleMessageProcessingOptions): Promise<void> {
   try {
-    const request: MessageCreateParams = req.body
-
-    // Use provided modelId or keep original model
-    if (modelId) {
-      request.model = modelId
-    }
-
-    // Validate request
     const validation = messagesService.validateRequest(request)
     if (!validation.isValid) {
-      return res.status(400).json({
+      res.status(400).json({
         type: 'error',
         error: {
           type: 'invalid_request_error',
           message: validation.errors.join('; ')
         }
       })
-    }
-
-    logger.info('Processing anthropic messages request', {
-      provider: provider.id,
-      apiHost: provider.apiHost,
-      anthropicApiHost: provider.anthropicApiHost,
-      model: request.model,
-      stream: request.stream,
-      thinking: request.thinking
-    })
-
-    // Handle streaming
-    if (request.stream) {
-      await handleStreamingResponse(res, request, provider, messagesService)
       return
     }
 
-    // Handle non-streaming
-    const response = await messagesService.processMessage(request, provider)
-    return res.json(response)
+    const extraHeaders = messagesService.prepareHeaders(req.headers)
+    const { client, anthropicRequest } = await messagesService.processMessage({
+      provider,
+      request,
+      extraHeaders,
+      modelId
+    })
+
+    if (request.stream) {
+      await messagesService.handleStreaming(client, anthropicRequest, { response: res }, provider)
+      return
+    }
+
+    const response = await client.messages.create(anthropicRequest)
+    res.json(response)
   } catch (error: any) {
-    return handleErrorResponse(res, error)
+    logger.error('Message processing error', { error })
+    const { statusCode, errorResponse } = messagesService.transformError(error)
+    res.status(statusCode).json(errorResponse)
   }
 }
 
@@ -338,10 +234,11 @@ router.post('/', async (req: Request, res: Response) => {
     const provider = modelValidation.provider!
     const modelId = modelValidation.modelId!
 
-    // Use shared processing function
-    return await processMessageRequest(req, res, provider, modelId)
+    return handleMessageProcessing({ req, res, provider, request, modelId })
   } catch (error: any) {
-    return handleErrorResponse(res, error)
+    logger.error('Message processing error', { error })
+    const { statusCode, errorResponse } = messagesService.transformError(error)
+    return res.status(statusCode).json(errorResponse)
   }
 })
 
@@ -493,10 +390,13 @@ providerRouter.post('/', async (req: Request, res: Response) => {
       })
     }
 
-    // Use shared processing function (no modelId override needed)
-    return await processMessageRequest(req, res, provider)
+    const request: MessageCreateParams = req.body
+
+    return handleMessageProcessing({ req, res, provider, request })
   } catch (error: any) {
-    return handleErrorResponse(res, error)
+    logger.error('Message processing error', { error })
+    const { statusCode, errorResponse } = messagesService.transformError(error)
+    return res.status(statusCode).json(errorResponse)
   }
 })
 

src/main/apiServer/services/messages.ts

@@ -1,33 +1,93 @@
 import Anthropic from '@anthropic-ai/sdk'
-import { Message, MessageCreateParams, RawMessageStreamEvent } from '@anthropic-ai/sdk/resources'
+import { MessageCreateParams, MessageStreamEvent } from '@anthropic-ai/sdk/resources'
 import { loggerService } from '@logger'
 import anthropicService from '@main/services/AnthropicService'
 import { buildClaudeCodeSystemMessage, getSdkClient } from '@shared/anthropic'
 import { Provider } from '@types'
+import { Response } from 'express'
 
 const logger = loggerService.withContext('MessagesService')
+const EXCLUDED_FORWARD_HEADERS: ReadonlySet<string> = new Set([
+  'host',
+  'x-api-key',
+  'authorization',
+  'sentry-trace',
+  'baggage',
+  'content-length',
+  'connection'
+])
 
 export interface ValidationResult {
   isValid: boolean
   errors: string[]
 }
 
+export interface ErrorResponse {
+  type: 'error'
+  error: {
+    type: string
+    message: string
+    requestId?: string
+  }
+}
+
+export interface StreamConfig {
+  response: Response
+  onChunk?: (chunk: MessageStreamEvent) => void
+  onError?: (error: any) => void
+  onComplete?: () => void
+}
+
+export interface ProcessMessageOptions {
+  provider: Provider
+  request: MessageCreateParams
+  extraHeaders?: Record<string, string | string[]>
+  modelId?: string
+}
+
+export interface ProcessMessageResult {
+  client: Anthropic
+  anthropicRequest: MessageCreateParams
+}
+
 export class MessagesService {
-  // oxlint-disable-next-line no-unused-vars
   validateRequest(request: MessageCreateParams): ValidationResult {
     // TODO: Implement comprehensive request validation
     const errors: string[] = []
 
-    if (!request.model) {
+    if (!request.model || typeof request.model !== 'string') {
       errors.push('Model is required')
     }
 
-    if (!request.max_tokens || request.max_tokens < 1) {
-      errors.push('max_tokens is required and must be at least 1')
+    if (typeof request.max_tokens !== 'number' || !Number.isFinite(request.max_tokens) || request.max_tokens < 1) {
+      errors.push('max_tokens is required and must be a positive number')
     }
 
     if (!request.messages || !Array.isArray(request.messages) || request.messages.length === 0) {
       errors.push('messages is required and must be a non-empty array')
+    } else {
+      request.messages.forEach((message, index) => {
+        if (!message || typeof message !== 'object') {
+          errors.push(`messages[${index}] must be an object`)
+          return
+        }
+
+        if (!('role' in message) || typeof message.role !== 'string' || message.role.trim().length === 0) {
+          errors.push(`messages[${index}].role is required`)
+        }
+
+        const content: unknown = message.content
+        if (content === undefined || content === null) {
+          errors.push(`messages[${index}].content is required`)
+          return
+        }
+
+        if (typeof content === 'string' && content.trim().length === 0) {
+          errors.push(`messages[${index}].content cannot be empty`)
+        } else if (Array.isArray(content) && content.length === 0) {
+          errors.push(`messages[${index}].content must include at least one item when using an array`)
+        }
+      })
     }
 
     return {
@@ -36,79 +96,224 @@ export class MessagesService {
     }
   }
 
-  async getClient(provider: Provider): Promise<Anthropic> {
+  async getClient(provider: Provider, extraHeaders?: Record<string, string | string[]>): Promise<Anthropic> {
     // Create Anthropic client for the provider
     if (provider.authType === 'oauth') {
       const oauthToken = await anthropicService.getValidAccessToken()
-      return getSdkClient(provider, oauthToken)
+      return getSdkClient(provider, oauthToken, extraHeaders)
     }
-    return getSdkClient(provider)
+    return getSdkClient(provider, null, extraHeaders)
   }
 
-  async processMessage(request: MessageCreateParams, provider: Provider): Promise<Message> {
-    logger.debug('Preparing Anthropic message request', {
-      model: request.model,
-      messageCount: request.messages.length,
-      stream: request.stream,
-      maxTokens: request.max_tokens,
-      provider: provider.id
-    })
+  prepareHeaders(headers: Record<string, string | string[] | undefined>): Record<string, string | string[]> {
+    const extraHeaders: Record<string, string | string[]> = {}
 
-    // Create Anthropic client for the provider
-    const client = await this.getClient(provider)
+    for (const [key, value] of Object.entries(headers)) {
+      if (value === undefined) {
+        continue
+      }
 
-    // Prepare request with the actual model ID
+      const normalizedKey = key.toLowerCase()
+      if (EXCLUDED_FORWARD_HEADERS.has(normalizedKey)) {
+        continue
+      }
+
+      extraHeaders[normalizedKey] = value
+    }
+
+    return extraHeaders
+  }
+
+  createAnthropicRequest(request: MessageCreateParams, provider: Provider, modelId?: string): MessageCreateParams {
     const anthropicRequest: MessageCreateParams = {
       ...request,
-      stream: false
+      stream: !!request.stream
     }
 
-    if (provider.authType === 'oauth') {
-      anthropicRequest.system = buildClaudeCodeSystemMessage(request.system || '')
+    // Override model if provided
+    if (modelId) {
+      anthropicRequest.model = modelId
     }
 
-    const response = await client.messages.create(anthropicRequest)
+    // Add Claude Code system message for OAuth providers
+    if (provider.type === 'anthropic' && provider.authType === 'oauth') {
+      anthropicRequest.system = buildClaudeCodeSystemMessage(request.system)
+    }
 
-    logger.info('Anthropic message completed', {
-      model: request.model,
-      provider: provider.id
-    })
-    return response
+    return anthropicRequest
   }
 
-  async *processStreamingMessage(
+  async handleStreaming(
+    client: Anthropic,
     request: MessageCreateParams,
+    config: StreamConfig,
     provider: Provider
-  ): AsyncIterable<RawMessageStreamEvent> {
-    logger.debug('Preparing streaming Anthropic message request', {
-      model: request.model,
-      messageCount: request.messages.length,
-      provider: provider.id
+  ): Promise<void> {
+    const { response, onChunk, onError, onComplete } = config
+
+    // Set streaming headers
+    response.setHeader('Content-Type', 'text/event-stream; charset=utf-8')
+    response.setHeader('Cache-Control', 'no-cache, no-transform')
+    response.setHeader('Connection', 'keep-alive')
+    response.setHeader('X-Accel-Buffering', 'no')
+    response.flushHeaders()
+
+    const flushableResponse = response as Response & { flush?: () => void }
+    const flushStream = () => {
+      if (typeof flushableResponse.flush !== 'function') {
+        return
+      }
+      try {
+        flushableResponse.flush()
+      } catch (flushError: unknown) {
+        logger.warn('Failed to flush streaming response', { error: flushError })
+      }
+    }
+
+    const writeSse = (eventType: string | undefined, payload: unknown) => {
+      if (response.writableEnded || response.destroyed) {
+        return
+      }
+
+      if (eventType) {
+        response.write(`event: ${eventType}\n`)
+      }
+
+      const data = typeof payload === 'string' ? payload : JSON.stringify(payload)
+      response.write(`data: ${data}\n\n`)
+      flushStream()
+    }
+
+    try {
+      const stream = client.messages.stream(request)
+      for await (const chunk of stream) {
+        if (response.writableEnded || response.destroyed) {
+          logger.warn('Streaming response ended before stream completion', {
+            provider: provider.id,
+            model: request.model
+          })
+          break
+        }
+
+        writeSse(chunk.type, chunk)
+
+        if (onChunk) {
+          onChunk(chunk)
+        }
+      }
+      writeSse(undefined, '[DONE]')
+
+      if (onComplete) {
+        onComplete()
+      }
+    } catch (streamError: any) {
+      logger.error('Stream error', {
+        error: streamError,
+        provider: provider.id,
+        model: request.model,
+        apiHost: provider.apiHost,
+        anthropicApiHost: provider.anthropicApiHost
+      })
+      writeSse(undefined, {
+        type: 'error',
+        error: {
+          type: 'api_error',
+          message: 'Stream processing error'
+        }
+      })
+
+      if (onError) {
+        onError(streamError)
+      }
+    } finally {
+      if (!response.writableEnded) {
+        response.end()
+      }
+    }
+  }
+
+  transformError(error: any): { statusCode: number; errorResponse: ErrorResponse } {
+    let statusCode = 500
+    let errorType = 'api_error'
+    let errorMessage = 'Internal server error'
+
+    const anthropicStatus = typeof error?.status === 'number' ? error.status : undefined
+    const anthropicError = error?.error
+
+    if (anthropicStatus) {
+      statusCode = anthropicStatus
+    }
+
+    if (anthropicError?.type) {
+      errorType = anthropicError.type
+    }
+
+    if (anthropicError?.message) {
+      errorMessage = anthropicError.message
+    } else if (error instanceof Error && error.message) {
+      errorMessage = error.message
+    }
+
+    // Infer error type from message if not from Anthropic API
+    if (!anthropicStatus && error instanceof Error) {
+      const errorMessageText = error.message ?? ''
+
+      if (errorMessageText.includes('API key') || errorMessageText.includes('authentication')) {
+        statusCode = 401
+        errorType = 'authentication_error'
+      } else if (errorMessageText.includes('rate limit') || errorMessageText.includes('quota')) {
+        statusCode = 429
+        errorType = 'rate_limit_error'
+      } else if (errorMessageText.includes('timeout') || errorMessageText.includes('connection')) {
+        statusCode = 502
+        errorType = 'api_error'
+      } else if (errorMessageText.includes('validation') || errorMessageText.includes('invalid')) {
+        statusCode = 400
+        errorType = 'invalid_request_error'
+      }
+    }
+
+    const safeErrorMessage =
+      typeof errorMessage === 'string' && errorMessage.length > 0 ? errorMessage : 'Internal server error'
+
+    return {
+      statusCode,
+      errorResponse: {
+        type: 'error',
+        error: {
+          type: errorType,
+          message: safeErrorMessage,
+          requestId: error?.request_id
+        }
+      }
+    }
+  }
+
+  async processMessage(options: ProcessMessageOptions): Promise<ProcessMessageResult> {
+    const { provider, request, extraHeaders, modelId } = options
+
+    const client = await this.getClient(provider, extraHeaders)
+    const anthropicRequest = this.createAnthropicRequest(request, provider, modelId)
+
+    const messageCount = Array.isArray(request.messages) ? request.messages.length : 0
+
+    logger.info('Processing anthropic messages request', {
+      provider: provider.id,
+      apiHost: provider.apiHost,
+      anthropicApiHost: provider.anthropicApiHost,
+      model: anthropicRequest.model,
+      stream: !!anthropicRequest.stream,
+      // systemPrompt: JSON.stringify(!!request.system),
+      // messages: JSON.stringify(request.messages),
+      messageCount,
+      toolCount: Array.isArray(request.tools) ? request.tools.length : 0
     })
 
-    // Create Anthropic client for the provider
-    const client = await this.getClient(provider)
-
-    // Prepare streaming request
-    const streamingRequest: MessageCreateParams = {
-      ...request,
-      stream: true
+    // Return client and request for route layer to handle streaming/non-streaming
+    return {
+      client,
+      anthropicRequest
     }
-
-    if (provider.authType === 'oauth') {
-      streamingRequest.system = buildClaudeCodeSystemMessage(request.system || '')
-    }
-
-    const stream = client.messages.stream(streamingRequest)
-
-    for await (const chunk of stream) {
-      yield chunk
-    }
-
-    logger.info('Completed streaming Anthropic message', {
-      model: request.model,
-      provider: provider.id
-    })
   }
 }
 

src/main/services/agents/services/claudecode/index.ts

@@ -106,7 +106,13 @@ class ClaudeCodeService implements AgentServiceInterface {
         logger.warn('claude stderr', { chunk })
         errorChunks.push(chunk)
       },
-      systemPrompt: session.instructions ? session.instructions : { type: 'preset', preset: 'claude_code' },
+      systemPrompt: session.instructions
+        ? {
+            type: 'preset',
+            preset: 'claude_code',
+            append: session.instructions
+          }
+        : { type: 'preset', preset: 'claude_code' },
       settingSources: ['project'],
       includePartialMessages: true,
       permissionMode: session.configuration?.permission_mode,
@@ -136,6 +142,8 @@ class ClaudeCodeService implements AgentServiceInterface {
 
     if (lastAgentSessionId) {
       options.resume = lastAgentSessionId
+      // TODO: use fork session when we support branching sessions
+      // options.forkSession = true
     }
 
     logger.info('Starting Claude Code SDK query', {

src/renderer/src/aiCore/index_new.ts

@@ -14,6 +14,7 @@ import { addSpan, endSpan } from '@renderer/services/SpanManagerService'
 import { StartSpanParams } from '@renderer/trace/types/ModelSpanEntity'
 import type { Assistant, GenerateImageParams, Model, Provider } from '@renderer/types'
 import type { AiSdkModel, StreamTextParams } from '@renderer/types/aiCoreTypes'
+import { buildClaudeCodeSystemModelMessage } from '@shared/anthropic'
 import { type ImageModel, type LanguageModel, type Provider as AiSdkProvider, wrapLanguageModel } from 'ai'
 
 import AiSdkToChunkAdapter from './chunk/AiSdkToChunkAdapter'
@@ -21,7 +22,6 @@ import LegacyAiProvider from './legacy/index'
 import { CompletionsParams, CompletionsResult } from './legacy/middleware/schemas'
 import { AiSdkMiddlewareConfig, buildAiSdkMiddlewares } from './middleware/AiSdkMiddlewareBuilder'
 import { buildPlugins } from './plugins/PluginBuilder'
-import { buildClaudeCodeSystemMessage } from './provider/config/anthropic'
 import { createAiSdkProvider } from './provider/factory'
 import {
   getActualProvider,
@@ -122,13 +122,9 @@ export default class ModernAiProvider {
     }
 
     if (this.actualProvider.id === 'anthropic' && this.actualProvider.authType === 'oauth') {
-      const claudeCodeSystemMessage = buildClaudeCodeSystemMessage(params.system)
+      const claudeCodeSystemMessage = buildClaudeCodeSystemModelMessage(params.system)
       params.system = undefined // 清除原有system，避免重复
-      if (Array.isArray(params.messages)) {
-        params.messages = [...claudeCodeSystemMessage, ...params.messages]
-      } else {
-        params.messages = claudeCodeSystemMessage
-      }
+      params.messages = [...claudeCodeSystemMessage, ...(params.messages || [])]
     }
 
     if (config.topicId && getEnableDeveloperMode()) {

src/renderer/src/aiCore/provider/config/anthropic.ts

@@ -1,24 +0,0 @@
-import { SystemModelMessage } from 'ai'
-
-export function buildClaudeCodeSystemMessage(system?: string): Array<SystemModelMessage> {
-  const defaultClaudeCodeSystem = `You are Claude Code, Anthropic's official CLI for Claude.`
-  if (!system || system.trim() === defaultClaudeCodeSystem) {
-    return [
-      {
-        role: 'system',
-        content: defaultClaudeCodeSystem
-      }
-    ]
-  }
-
-  return [
-    {
-      role: 'system',
-      content: defaultClaudeCodeSystem
-    },
-    {
-      role: 'system',
-      content: system
-    }
-  ]
-}