feat(hub): 结构化运行历史(A-3) + lock 心跳(A-5)

A-3 结构化历史:
- 新增 AgentMessage 表(每条消息的 queryable 投影,transcript 文件仍是 agent 读回记忆)
- 新增 AgentFileChange 表(run 期间文件变更 before/after hash + operation)
- runner.ts: generateText 后 persistAgentMessages 落库 result.responseMessages
- workspace.ts writeFileTool: 写前算 beforeHash(SHA-256),写后算 afterHash,通过 ctx.onFileChange sink 记录
- runner.ts flushFileChanges: 收集 sink 的变更批量写入 AgentFileChange
- ToolContext 加 onFileChange sink 字段
- trigger.ts 接线 runId/sessionId/prisma 到 RunRequest

A-5 lock 心跳:
- ProjectAgentLock 加 heartbeatAt 列
- runner.ts onStepFinish 回调:每步 model step 后更新 heartbeatAt(吞错,lock 可能被 force-release)

60 tests 全过(tsc 干净)。

hub/src/agent/workspace.ts

@@ -8,6 +8,7 @@
  * surface; the Hub agent is narrower than a general coding agent.
  */
 import { readFile, writeFile, readdir, mkdir } from "node:fs/promises";
+import { createHash } from "node:crypto";
 import { join, resolve, relative, isAbsolute } from "node:path";
 import { tool } from "ai";
 import { z } from "zod";
@@ -67,8 +68,39 @@ export function writeFileTool(ctx: ToolContext): ToolDefinition {
     execute: async (args): Promise<string> => {
       try {
         const full = confine(args.path, ctx.workspaceDir);
+        // A-3 file-change capture: compute before/after hashes around the write.
+        // A hashing failure must not block the write — skip the sink in that case.
+        let beforeHash: string | null = null;
+        let afterHash: string | null = null;
+        let operation: "CREATE" | "UPDATE" | null = null;
+        try {
+          let oldContent: string | null;
+          try {
+            oldContent = await readFile(full, "utf8");
+          } catch (e) {
+            if (e !== null && typeof e === "object" && "code" in e && e.code === "ENOENT") {
+              oldContent = null;
+            } else {
+              throw e;
+            }
+          }
+          afterHash = createHash("sha256").update(args.content).digest("hex");
+          beforeHash = oldContent === null ? null : createHash("sha256").update(oldContent).digest("hex");
+          if (beforeHash === null) {
+            operation = "CREATE";
+          } else if (beforeHash === afterHash) {
+            operation = null;
+          } else {
+            operation = "UPDATE";
+          }
+        } catch {
+          operation = null;
+        }
         await mkdir(join(full, ".."), { recursive: true });
         await writeFile(full, args.content, "utf8");
+        if (operation !== null && ctx.onFileChange !== undefined) {
+          ctx.onFileChange({ path: args.path, operation, beforeHash, afterHash, diff: null });
+        }
         return JSON.stringify({ ok: true, path: args.path, bytes: args.content.length });
       } catch (e) {
         return JSON.stringify({ error: e instanceof Error ? e.message : String(e) });