fix(backlog): 修评审 3 HIGH — resume chain_key 真值 / 模板空白校验 / 续写链 resume E2E

1. resume_chain 回报真 chain_key：从 awaiting job.result 读回（run 时 _chain_result
   持久化），不再按 job.kind 推断（kind 恒为通用常量 "chain"，从不在 SUPPORTED_CHAINS
   → 总错回退 draft_volume）。continue_volume 的 resume 回执现报真值。
2. 模板 title/body 拒纯空白：StringConstraints(strip_whitespace, min_length=1)，
   "   " strip 后为空 → 422。
3. 续写链 resume 路径 E2E：continue_volume 第 1 章冲突 → interrupt → awaiting →
   resume 带裁决 → done，断言 resume 回执 / job result chain_key="continue_volume"
   （回归守卫 #1）。

测试：+resume continue_volume 单测（chain_key 真值）+2 模板空白 422 单测 +1 续写链
resume E2E。重生成 TS 客户端（仅 description 文案变化）。

apps/api/tests/test_chain.py

@@ -365,6 +365,31 @@ async def test_resume_chain_awaiting_returns_202(
     assert len(_noop_run_chain_job) == 1
 
 
+async def test_resume_continue_volume_reports_true_chain_key(
+    _noop_run_chain_job: list[dict[str, Any]],
+) -> None:
+    """回归守卫 #1：resume continue_volume run → 回执 chain_key="continue_volume"（读自
+    job.result，run 时由 _chain_result 持久化），而非旧 bug 按 job.kind 推断的 "draft_volume"。
+    且转发给 run_chain_job 的 chain_key 也是真值（续写模式不被错降为 draft_volume）。"""
+    project_repo = FakeProjectRepo()
+    job_repo = FakeJobRepo()
+    pid = await _seed_project(project_repo)
+    job = await job_repo.create(pid, "chain")  # kind 恒为通用常量 "chain"
+    # run 时 interrupt 把真 chain_key 持久进 result（continue_volume）。
+    await job_repo.set_awaiting(job.id, {"awaiting_chapter": 1, "chain_key": "continue_volume"})
+    app = _app(project_repo, job_repo)
+
+    async with _client(app) as client:
+        resp = await client.post(
+            f"/projects/{pid}/chains/runs/{job.id}/resume",
+            json={"decisions": [{"conflict_index": 0, "verdict": "ignore"}]},
+        )
+
+    assert resp.status_code == 202
+    assert resp.json()["chain_key"] == "continue_volume"
+    assert _noop_run_chain_job[0]["kwargs"]["chain_key"] == "continue_volume"
+
+
 async def test_resume_chain_non_awaiting_returns_409(
     _noop_run_chain_job: list[dict[str, Any]],
 ) -> None:

apps/api/tests/test_templates.py

@@ -105,6 +105,23 @@ async def test_create_template_empty_body_returns_422() -> None:
     assert resp.status_code == 422
 
 
+@pytest.mark.asyncio
+async def test_create_template_whitespace_only_title_returns_422() -> None:
+    # strip 后为空 → min_length=1 不满足 → 422（防纯空白标题，审评 #2）。
+    client, _repo, _session = _make_client()
+    async with client:
+        resp = await client.post("/templates", json={"title": "   ", "body": "b"})
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_create_template_whitespace_only_body_returns_422() -> None:
+    client, _repo, _session = _make_client()
+    async with client:
+        resp = await client.post("/templates", json={"title": "a", "body": "   "})
+    assert resp.status_code == 422
+
+
 @pytest.mark.asyncio
 async def test_delete_template_returns_204_and_commits() -> None:
     client, repo, session = _make_client()