refactor(hub): 手搓 agent loop 换成 Vercel AI SDK

将 provider/runner/tools 三件手搓轮子替换为 AI SDK v7 的 generateText + tool:
- 删 openrouter-provider.ts(翻译层消失)、provider.ts 自定义消息类型
- runner.ts 循环体改为 generateText({stopWhen: stepCountIs}),保留 RunRequest/RunResult 公共签名
- tools.ts ToolRegistry 改为 ToolFactory + build(ctx, names?) 按 role 白名单构建 tools record
- workspace/cph/feishu 工具改写为 tool() 定义,execute 闭包捕获 per-run ToolContext
- transcript.ts 改为 ModelMessage[] JSONL(0.0.0 cutover,无迁移)
- server.ts/trigger.ts 接 modelFactory + toolWhitelist
- 测试:helpers 写 MockLanguageModel implements LanguageModelV4;5 个测试改写 + 新增 runner.test.ts
- 移除未使用的 openai 依赖
- ADR-0017 Consequences 同步:loop 委托给 AI SDK,provider seam 是 LanguageModel

tsc 干净,54 tests 全过。

hub/src/agent/transcript.ts

@@ -1,7 +1,7 @@
 /**
  * Session transcript — append-only JSONL file in the workspace.
  *
- * Each line is one {@link Message}, JSON-encoded. The transcript lives at
+ * Each line is one AI SDK {@link ModelMessage}, JSON-encoded. The transcript lives at
  * `workspaceDir/.cph/sessions/<sessionId>.jsonl`, following the same "workspace
  * is a directory tree" principle as the engineering file itself (ADR-0007).
  *
@@ -15,9 +15,9 @@
  * distinct; storing session messages does not conflict with "the Hub avoids
  * becoming a full chat history store."
  */
-import { readFile, writeFile, mkdir, appendFile } from "node:fs/promises";
+import { readFile, mkdir, appendFile } from "node:fs/promises";
 import { join, dirname } from "node:path";
-import type { Message } from "./provider.js";
+import type { ModelMessage } from "ai";
 
 /// Subdirectory within a workspace where session transcripts live.
 export const TRANSCRIPT_DIR = ".cph/sessions";
@@ -33,19 +33,19 @@ export function transcriptPath(workspaceDir: string, sessionId: string): string
  * skipped — a partially-written last line (crash mid-append) won't break the
  * next run.
  */
-export async function readTranscript(path: string): Promise<Message[]> {
+export async function readTranscript(path: string): Promise<ModelMessage[]> {
   let content: string;
   try {
     content = await readFile(path, "utf8");
   } catch {
     return [];
   }
-  const messages: Message[] = [];
+  const messages: ModelMessage[] = [];
   for (const line of content.split("\n")) {
     const trimmed = line.trim();
     if (trimmed === "") continue;
     try {
-      messages.push(JSON.parse(trimmed) as Message);
+      messages.push(JSON.parse(trimmed) as ModelMessage);
     } catch {
       // Skip corrupt line — likely a partial write from a crash.
     }
@@ -57,7 +57,7 @@ export async function readTranscript(path: string): Promise<Message[]> {
  * Append messages to a transcript file. Creates the parent directory if needed.
  * Each message is written as one JSON line.
  */
-export async function appendTranscript(path: string, messages: readonly Message[]): Promise<void> {
+export async function appendTranscript(path: string, messages: readonly ModelMessage[]): Promise<void> {
   await mkdir(dirname(path), { recursive: true });
   const lines = messages.map((m) => JSON.stringify(m)).join("\n") + "\n";
   await appendFile(path, lines, "utf8");