refactor: extract @uncaged/workflow-util-agent + smart prompt

- New package: spawn-cli + build-agent-prompt shared utils
- Smart prompt: start + meta summaries for middle steps + last step full
- Cursor/Hermes adapters now import from util-agent (no duplicate code)
- 109 tests pass, biome clean

Closes #14
小橘 <xiaoju@shazhou.work>

packages/workflow-util-agent/__tests__/spawn-cli.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, test } from "bun:test";
+
+import { spawnCli } from "../src/index.js";
+
+const noTimeout = { cwd: null, timeoutMs: null } as const;
+
+describe("spawnCli", () => {
+  test("resolves ok stdout on zero exit", async () => {
+    const run = await spawnCli("echo", ["spawn-cli-ok"], { ...noTimeout });
+    expect(run.ok).toBe(true);
+    if (run.ok) {
+      expect(run.value.trim()).toBe("spawn-cli-ok");
+    }
+  });
+
+  test("resolves err on non-zero exit", async () => {
+    const run = await spawnCli("false", [], { ...noTimeout });
+    expect(run.ok).toBe(false);
+    if (!run.ok) {
+      expect(run.error.kind).toBe("non_zero_exit");
+    }
+  });
+
+  test("resolves err on timeout", async () => {
+    const run = await spawnCli("sleep", ["10"], { cwd: null, timeoutMs: 80 });
+    expect(run.ok).toBe(false);
+    if (!run.ok) {
+      expect(run.error.kind).toBe("timeout");
+    }
+  });
+
+  test("resolves err when spawn fails", async () => {
+    const run = await spawnCli("definitely-missing-executable-7f2a9c1b", [], { ...noTimeout });
+    expect(run.ok).toBe(false);
+    if (!run.ok) {
+      expect(run.error.kind).toBe("spawn_failed");
+    }
+  });
+});