Gate live tests on one sentinel var each, fail on partial config

Skipping now keys solely on NISSE_LLM_BASE_URL and
NISSE_MATRIX_HOMESERVER: if the sentinel is set, the live path is
expected to work and any other missing variable is an assertion
failure naming it, not a silent skip. A misnamed or misplaced CI
secret previously produced a green run with no live coverage.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/integration/test_llm_live.py

@@ -1,8 +1,9 @@
 """Live smoke test against the real LiteLLM proxy.
 
-Skips unless NISSE_LLM_BASE_URL, NISSE_LLM_TOKEN, and NISSE_ROLE_EXECUTOR are
-present (from the environment or the repo-root .env) — CI stays credential-free
-by choice; this runs from the operator's machine.
+NISSE_LLM_BASE_URL alone decides whether this runs: if it is set, the live
+path is expected to work, and anything else missing is a *failure*, not a
+skip. A half-configured environment must not pass quietly as a skip — that is
+how a broken CI credential hides.
 """
 
 import os
@@ -16,18 +17,24 @@ from nisse_dev.llm import LiteLLMClient
 
 load_env_file(Path(__file__).resolve().parents[2] / ".env")
 
-REQUIRED = ("NISSE_LLM_BASE_URL", "NISSE_LLM_TOKEN", "NISSE_ROLE_EXECUTOR")
+SENTINEL = "NISSE_LLM_BASE_URL"
+ALSO_REQUIRED = ("NISSE_LLM_TOKEN", "NISSE_ROLE_EXECUTOR")
 
 pytestmark = [
     pytest.mark.integration,
     pytest.mark.skipif(
-        not all(os.environ.get(var) for var in REQUIRED),
-        reason=f"live LLM config absent; set {', '.join(REQUIRED)}",
+        not os.environ.get(SENTINEL),
+        reason=f"no live LLM configured ({SENTINEL} unset)",
     ),
 ]
 
 
 def test_executor_model_completes_via_litellm() -> None:
+    missing = [var for var in ALSO_REQUIRED if not os.environ.get(var)]
+    assert not missing, (
+        f"{SENTINEL} is set, so the live LLM path is expected to work, "
+        f"but these are missing: {', '.join(missing)}"
+    )
     client = LiteLLMClient.from_env()
     events = [
         StoredEvent(