refactor: 拆分 3 个过大 ACP 文件为模块化子文件（每个 <500 行）

通过 4 阶段 workflow（分析 → 计划 → 重构 → 验证）将 3 个超大的 ACP
源文件拆分为 28 个模块化子文件，每个均严格小于 500 行，且完整保留
所有公共 API（barrel 模式重导出）。

变更概要：
- packages/acp-link/src/server.ts: 1800 → 20 行（barrel），新增 11 个子模块
  （server/types、payload-decode、permission-mode、runtime-state、dispatch、
  handlers-agent、handlers-session、acp-client、client-send、start-server、
  testing-internals）
- src/services/acp/agent.ts: 1297 → 33 行（barrel），新增 9 个子模块
  （agent/AcpAgent、sessionTypes、permissionMode、configOptions、promptQueue、
  internalAccessors、createSessionMethod、sessionLifecycle、promptFlow）
- src/services/acp/bridge.ts: 1516 → 29 行（barrel），新增 8 个子模块
  （bridge/types、paths、contentBlocks、toolInfo、toolResults、modelUsage、
  notifications、forwarding）

验证：
- bun run precheck 全通过（typecheck + lint + 5851 tests）
- ACP service tests: 176 pass / 0 fail
- ACP link tests: 47 pass / 0 fail
- 所有外部消费者（entry.ts、permissions.ts、__tests__/）的 import 路径不变
- 测试文件零修改

迁移计划详见 docs/acp-refactor-plan.md。

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

src/services/acp/bridge/contentBlocks.ts

@@ -0,0 +1,146 @@
+// Low-level conversion of Claude content block shapes into ACP ContentBlock values.
+import type { ContentBlock, ToolCallContent } from './types.js'
+
+/**
+ * Wraps a string or array of content blocks into a `{ content: ToolCallContent[] }`
+ * update object. Used by `toolUpdateFromToolResult` for the default / error paths.
+ */
+export function toAcpContentUpdate(
+  content: unknown,
+  isError: boolean,
+): { content?: ToolCallContent[] } {
+  if (Array.isArray(content) && content.length > 0) {
+    return {
+      content: content.map((c: Record<string, unknown>) => ({
+        type: 'content' as const,
+        content: toAcpContentBlock(c, isError),
+      })),
+    }
+  }
+  if (typeof content === 'string' && content.length > 0) {
+    return {
+      content: [
+        {
+          type: 'content' as const,
+          content: {
+            type: 'text' as const,
+            text: isError ? `\`\`\`\n${content}\n\`\`\`` : content,
+          },
+        },
+      ],
+    }
+  }
+  return {}
+}
+
+export function toAcpContentBlock(
+  content: Record<string, unknown>,
+  isError: boolean,
+): ContentBlock {
+  const wrapText = (text: string): ContentBlock => ({
+    type: 'text',
+    text: isError ? `\`\`\`\n${text}\n\`\`\`` : text,
+  })
+
+  const type = content.type as string
+  switch (type) {
+    case 'text': {
+      const text = content.text as string
+      return { type: 'text', text: isError ? `\`\`\`\n${text}\n\`\`\`` : text }
+    }
+    case 'image': {
+      const source = content.source as Record<string, unknown> | undefined
+      if (source?.type === 'base64') {
+        return {
+          type: 'image',
+          data: source.data as string,
+          mimeType: source.media_type as string,
+        }
+      }
+      return wrapText(
+        source?.type === 'url'
+          ? `[image: ${source.url as string}]`
+          : '[image: file reference]',
+      )
+    }
+    case 'resource_link': {
+      // ACP v1 ResourceLink requires name + uri. Name falls back to uri when
+      // absent so the client always has a display label. mimeType is optional.
+      const uri = content.uri as string | undefined
+      const name =
+        (content.name as string | undefined) ?? (uri as string | undefined)
+      return {
+        type: 'resource_link',
+        uri: uri as string,
+        name: name as string,
+        mimeType: content.mimeType as string | undefined,
+      }
+    }
+    case 'resource': {
+      // ACP v1 EmbeddedResource wraps an optional TextResource / BlobResource
+      // shape. Forward the standard fields the client knows how to render.
+      const r = content.resource as Record<string, unknown> | undefined
+      // Construct a TextResource or BlobResource payload depending on what is
+      // present. Cast through unknown because not every source shape satisfies
+      // the full union contract.
+      const resourcePayload = {
+        uri: (r?.uri as string | undefined) ?? '',
+        mimeType: r?.mimeType as string | null | undefined,
+        ...(typeof r?.text === 'string' ? { text: r.text as string } : {}),
+        ...(typeof r?.blob === 'string' ? { blob: r.blob as string } : {}),
+      }
+      return {
+        type: 'resource',
+        resource: resourcePayload,
+      } as unknown as ContentBlock
+    }
+    case 'tool_reference':
+      return wrapText(`Tool: ${content.tool_name as string}`)
+    case 'tool_search_tool_search_result': {
+      const refs = content.tool_references as
+        | Array<{ tool_name: string }>
+        | undefined
+      return wrapText(
+        `Tools found: ${refs?.map(r => r.tool_name).join(', ') || 'none'}`,
+      )
+    }
+    case 'tool_search_tool_result_error':
+      return wrapText(
+        `Error: ${content.error_code as string}${content.error_message ? ` - ${content.error_message as string}` : ''}`,
+      )
+    case 'web_search_result':
+      return wrapText(`${content.title as string} (${content.url as string})`)
+    case 'web_search_tool_result_error':
+      return wrapText(`Error: ${content.error_code as string}`)
+    case 'web_fetch_result':
+      return wrapText(`Fetched: ${content.url as string}`)
+    case 'web_fetch_tool_result_error':
+      return wrapText(`Error: ${content.error_code as string}`)
+    case 'code_execution_result':
+    case 'bash_code_execution_result':
+      return wrapText(
+        `Output: ${(content.stdout as string) || (content.stderr as string) || ''}`,
+      )
+    case 'code_execution_tool_result_error':
+    case 'bash_code_execution_tool_result_error':
+      return wrapText(`Error: ${content.error_code as string}`)
+    case 'text_editor_code_execution_view_result':
+      return wrapText(content.content as string)
+    case 'text_editor_code_execution_create_result':
+      return wrapText(content.is_file_update ? 'File updated' : 'File created')
+    case 'text_editor_code_execution_str_replace_result': {
+      const lines = content.lines as string[] | undefined
+      return wrapText(lines?.join('\n') || '')
+    }
+    case 'text_editor_code_execution_tool_result_error':
+      return wrapText(
+        `Error: ${content.error_code as string}${content.error_message ? ` - ${content.error_message as string}` : ''}`,
+      )
+    default:
+      try {
+        return { type: 'text', text: JSON.stringify(content) }
+      } catch {
+        return { type: 'text', text: '[content]' }
+      }
+  }
+}