test: keep gateway-dependent e2e out of the commit gate

The pre-commit hook runs the whole suite, and tests/e2e/ talks to a real
LLM gateway, so whether a commit is allowed depended on how fast that
gateway happened to be. During the issue 14 work it blocked two commits
on two different cases; both passed when rerun alone, and the suite went
from 165s to 336s that hour.

The wasted minutes are not the real cost. Retrying on red teaches you to
read "test failed" as "gateway was slow", and a genuinely flaky bug then
gets retried away too. An alarm that cries wolf stops being an alarm.

test_thinking_live.py already carried the slow marker; the other three
files now match it, and the release checklist gains an explicit
`pytest -m slow` step so they still run where a human is watching --
without that step this change would just delete the coverage.

Also raises test_flat_legacy_keys_assemble's LLM_TIMEOUT from 120 to
300, matching .env. At 120 the case allowed half of what production
allows, on a gateway that needs the full 300 -- it measured 116s in a
solo run. The assertion is that the flat key name parses into
SourceConfig.timeout_s; the value itself was never under test.

tests/e2e/test_compat_projects.py

@@ -18,9 +18,16 @@ _REPO = Path(__file__).resolve().parents[2]
 _ENV = {k: v for k, v in {**dotenv_values(".env"), **os.environ}.items() if v is not None}
 _HAS_SOURCE = any(k.split("__")[0] == "LLM" and k.endswith("__API_KEY") for k in _ENV)
 
-pytestmark = pytest.mark.skipif(
-    not _HAS_SOURCE, reason="需真实网关凭据: 在 .env 配置 LLM__{PROVIDER}__1__*"
-)
+# 真实网关调用: 与 test_thinking_live.py 同待遇标 slow(pytest addopts 默认排除,
+# 显式 `pytest -m slow` 运行)。理由是这些用例的成败取决于网关此刻快不快,而
+# pre-commit 关卡跑全套件——网关一抖就挡住与之无关的提交,久了会把"测试红了
+# 先怀疑网关"变成惯性,真 bug 也会被当成抖动重试掉。发版清单负责让它们真跑。
+pytestmark = [
+    pytest.mark.slow,
+    pytest.mark.skipif(
+        not _HAS_SOURCE, reason="需真实网关凭据: 在 .env 配置 LLM__{PROVIDER}__1__*"
+    ),
+]
 
 
 @pytest.fixture
@@ -69,7 +76,10 @@ class TestVideoTreeOnboarding:
         source_keys = {k: v for k, v in _ENV.items() if k.split("__")[0] == "LLM" and "__" in k}
         flat_env = {
             **source_keys,
-            "LLM_TIMEOUT": "120",
+            # 与 .env 的 LLM__MINIMAX__1__TIMEOUT_S 同值。取 120(VT 旧值)会让本用例的
+            # 超时比生产配置还紧一半,在慢网关上必然间歇红——而本用例断言的是平铺
+            # 键名能否解析成 SourceConfig.timeout_s,超时取值本身不是被测对象
+            "LLM_TIMEOUT": "300",
             "LLM_MAX_RETRIES": "3",
             "LLM_RETRY_BASE_DELAY": "2.0",
             "LLM_RETRY_MAX_DELAY": "30.0",