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>

packages/acp-link/src/server/client-send.ts

@@ -0,0 +1,89 @@
+import type { WSContext } from 'hono/ws'
+import { clients, getRcsUpstream } from './runtime-state.js'
+import type { ClientState } from './types.js'
+
+// Maps legacy notification type strings to their JSON-RPC method names so
+// agent→client notifications are also emitted as JSON-RPC notifications for
+// JSON-RPC 2.0 clients (audit §8.1). Notifications have no id.
+export const LEGACY_NOTIFICATION_TO_JSONRPC: Record<string, string> = {
+  session_update: 'session/update',
+  permission_request: 'session/request_permission',
+}
+
+// Send a notification/response to the WebSocket client.
+//
+// For legacy `{type, payload}` clients this emits the proprietary envelope.
+// For JSON-RPC 2.0 clients this additionally emits a JSON-RPC response that
+// echoes the in-flight request id when the message type matches the pending
+// request's expected response type (audit §8.2). Agent→client notifications
+// (`session_update`, `permission_request`) are emitted as JSON-RPC
+// notifications without an id.
+export function send(ws: WSContext, type: string, payload?: unknown): void {
+  if (ws.readyState === 1) {
+    // WebSocket.OPEN
+    ws.send(JSON.stringify({ type, payload }))
+  }
+  // Forward to RCS upstream if connected
+  const rcsUpstream = getRcsUpstream()
+  if (rcsUpstream?.isRegistered()) {
+    rcsUpstream.send({ type, payload })
+  }
+
+  const state = clients.get(ws)
+  if (!state?.jsonRpc) return
+
+  // If this is the response to an in-flight JSON-RPC request, emit the
+  // standard JSON-RPC result with the preserved id.
+  if (state.pendingJsonRpc?.responseType === type) {
+    sendJsonRpcRaw(ws, {
+      jsonrpc: '2.0',
+      id: state.pendingJsonRpc.id,
+      result: payload ?? {},
+    })
+    state.pendingJsonRpc = null
+    return
+  }
+
+  // Agent→client notifications are also emitted as JSON-RPC notifications
+  // (no id) so JSON-RPC clients receive them in their native format.
+  const notificationMethod = LEGACY_NOTIFICATION_TO_JSONRPC[type]
+  if (notificationMethod) {
+    sendJsonRpcRaw(ws, {
+      jsonrpc: '2.0',
+      method: notificationMethod,
+      params: payload ?? {},
+    })
+  }
+}
+
+// Serialize a JSON-RPC 2.0 message and send it to a connected WS client.
+export function sendJsonRpcRaw(ws: WSContext, message: object): void {
+  if (ws.readyState === 1) {
+    ws.send(JSON.stringify(message))
+  }
+}
+
+/**
+ * Send a JSON-RPC 2.0 error response with a reserved -32xxx code (audit §8.3).
+ * Also emits the legacy `{type: 'error', payload: {message}}` envelope for
+ * backwards compatibility.
+ */
+export function sendJsonRpcError(
+  ws: WSContext,
+  state: ClientState | undefined,
+  id: string | number | null,
+  code: number,
+  message: string,
+): void {
+  if (state?.jsonRpc) {
+    sendJsonRpcRaw(ws, {
+      jsonrpc: '2.0',
+      id,
+      error: { code, message },
+    })
+  } else {
+    send(ws, 'error', { message, code: String(code) })
+  }
+  // Error consumed the in-flight request, if any.
+  if (state) state.pendingJsonRpc = null
+}