fix: 严格对齐 ACP 协议实现到 stable v1 规范

对照 /Users/konghayao/code/knowledgebase/origin/acp 规范审计并修复 53 条合规性
发现（critical 5 / major 17 / minor 20 / nit 11），完整审计报告见
docs/acp-compliance-audit.md。

Agent 端 (src/services/acp/agent.ts):
- initialize() 补齐 authMethods，promptCapabilities.image 降级为 false（声明与
  实现脱节，按 initialization.mdx 不声明的 capability 视为不支持）
- sessionCapabilities.fork 移至 _meta.claudeCode.forkSession（fork 在
  meta.unstable.json 中，避免在 stable sessionCapabilities 中暴露 unstable 特性）
- unstable_resumeSession 传 replay:false，不再通过 session/update 重放历史
  （session-setup.mdx:239 明确禁止）
- PromptResponse.usage 移至 _meta.claudeCode.usage
  （extensibility.mdx:39 禁止在 spec 类型根添加自定义字段）
- 空字符串 prompt 改为显式 throw（不再误返 end_turn）

Bridge (src/services/acp/bridge.ts):
- 删除全部 usage_update discriminator（不在 stable v1 schema 中）
- 显式映射 refusal stop_reason（之前误报 end_turn）
- max_tokens / isError 检查互斥
- Read/Write/Edit/Glob 路径全部绝对化（协议规定路径 MUST 绝对）
- 补全 resource_link / resource ContentBlock 渲染

Permissions (src/services/acp/permissions.ts):
- 补齐 reject_always PermissionOption（schema 规定的四个 option 之一）
- checkTerminalOutput 优先检查标准 clientCapabilities.terminal，
  回退到 _meta.terminal_output
- 新增 onPermissionCancelled 回调：cancelled permission outcome →
  StopReason::Cancelled（schema.json:629）
- ExitPlanMode cancelled 分支补上 toolUseID 字段

PromptConversion (src/services/acp/promptConversion.ts):
- resource 分支处理 BlobResource（之前静默丢弃 blob 内容）

acp-link 代理 (packages/acp-link/src/):
- WS 协议从专有 {type, payload} 改造为标准 JSON-RPC 2.0
  （transports.mdx:52 要求自定义 transport MUST 保留 JSON-RPC 消息格式），
  同时向后兼容旧 envelope
- 实现 $/cancel_request 处理
- 使用 JSON-RPC 标准错误码 -32700 / -32600 / -32601 / -32602 / -32603
- capability / agentInfo / protocolVersion 完整透传

验证：bun run precheck 全部通过（tsc 零错误、biome ci 零警告、5841/5841 测试通过）；
ACP 专项测试 221/221 通过。独立 verification agent 抽查全部 PASS。

已知暂缓项（审计文档附录 B/C）：
- §3.5 traceparent/trace-context 传播（QueryEngine 无 header hook）
- §5.2 terminal/create 完整生命周期（P1，非阻断，需新 RPC 流程）
- §4.2 in_progress tool_call status（SHOULD 级）
- §8.8/8.9/8.14 stale types.ts（不在 owner 分配集合，runtime 已修正）

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

packages/acp-link/src/ws-message.ts

@@ -7,12 +7,65 @@ export class WsPayloadTooLargeError extends Error {
   }
 }
 
+/**
+ * Legacy proprietary envelope shape: `{ type, payload? }`.
+ * Retained for backwards compatibility with older clients (e.g. the RCS Web UI)
+ * that have not migrated to JSON-RPC 2.0 yet.
+ */
 export interface JsonWsMessage {
   type: string
   payload?: unknown
   [key: string]: unknown
 }
 
+/**
+ * JSON-RPC 2.0 envelope as defined by the specification.
+ * See transports.mdx: custom transports MUST preserve the JSON-RPC message
+ * format and lifecycle requirements defined by ACP.
+ */
+export interface JsonRpc2Request {
+  jsonrpc: '2.0'
+  id: string | number | null
+  method: string
+  params?: unknown
+}
+
+export interface JsonRpc2Notification {
+  jsonrpc: '2.0'
+  method: string
+  params?: unknown
+}
+
+export interface JsonRpc2Response {
+  jsonrpc: '2.0'
+  id: string | number | null
+  result?: unknown
+  error?: { code: number; message: string; data?: unknown }
+}
+
+export type JsonRpc2Message =
+  | JsonRpc2Request
+  | JsonRpc2Notification
+  | JsonRpc2Response
+
+/**
+ * Messages that carry a `method` field — i.e. requests and notifications that
+ * the proxy can route. Responses (no method) are excluded because clients are
+ * not expected to send them to the agent.
+ */
+export type JsonRpc2ClientMessage = JsonRpc2Request | JsonRpc2Notification
+
+export function isJsonRpc2Message(
+  value: unknown,
+): value is JsonRpc2ClientMessage {
+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    (value as { jsonrpc?: unknown }).jsonrpc === '2.0' &&
+    typeof (value as { method?: unknown }).method === 'string'
+  )
+}
+
 function assertPayloadSize(byteLength: number): void {
   if (byteLength > MAX_CLIENT_WS_PAYLOAD_BYTES) {
     throw new WsPayloadTooLargeError(byteLength)
@@ -49,14 +102,28 @@ function decodeWsText(data: unknown): string {
   throw new Error('Unsupported WebSocket message payload')
 }
 
+/**
+ * Decode a WebSocket text frame into either a JSON-RPC 2.0 message or the
+ * legacy proprietary `{type, payload}` envelope.
+ *
+ * Accepts:
+ * - JSON-RPC 2.0 requests/notifications/responses (`{ jsonrpc: '2.0', method, ... }`)
+ * - Legacy proprietary messages (`{ type: string, payload?: unknown }`)
+ *
+ * Rejects anything else with `Invalid WebSocket message payload`.
+ */
 export function decodeJsonWsMessage(data: unknown): JsonWsMessage {
   const parsed = JSON.parse(decodeWsText(data)) as unknown
-  if (
-    typeof parsed !== 'object' ||
-    parsed === null ||
-    !('type' in parsed) ||
-    typeof parsed.type !== 'string'
-  ) {
+  if (typeof parsed !== 'object' || parsed === null) {
+    throw new Error('Invalid WebSocket message payload')
+  }
+  // JSON-RPC 2.0 envelope — preserve all original fields so the router can
+  // correlate request ids and forward notifications unchanged.
+  if (isJsonRpc2Message(parsed)) {
+    return parsed as unknown as JsonWsMessage
+  }
+  // Legacy proprietary envelope `{ type, payload? }`.
+  if (!('type' in parsed) || typeof parsed.type !== 'string') {
     throw new Error('Invalid WebSocket message payload')
   }
   return parsed as JsonWsMessage