fix(tests): anchor VCR redis cassette key to repo root

`os.path.relpath` with no `start` arg uses the current working
directory, so running pytest from a subdirectory produced a
different Redis key than running from the repo root. CI-recorded
cassettes and locally-replayed runs would silently miss each
other's cache.

Anchor the path to the repo root (derived from `__file__`) so the
key is stable regardless of CWD.

https://claude.ai/code/session_018uCx7pcrkdUJZrCVMaTdPx

tests/_vcr_redis_persister.py

@@ -13,6 +13,8 @@ CASSETTE_REDIS_URL_ENV = "CASSETTE_REDIS_URL"
 VCR_VERBOSE_ENV = "LITELLM_VCR_VERBOSE"
 MAX_EPISODES_PER_CASSETTE = 50
 
+_REPO_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
 _log = logging.getLogger(__name__)
 _passed_by_cassette_key: dict[str, bool] = {}
 
@@ -22,7 +24,11 @@ def mark_test_outcome_for_cassette(cassette_path: str, passed: bool) -> None:
 
 
 def redis_key_for(cassette_path: str) -> str:
-    rel = os.path.relpath(str(cassette_path))
+    abs_path = os.path.abspath(str(cassette_path))
+    try:
+        rel = os.path.relpath(abs_path, start=_REPO_ROOT)
+    except ValueError:
+        rel = os.path.basename(abs_path)
     if rel.endswith(".yaml"):
         rel = rel[: -len(".yaml")]
     rel = rel.replace("/cassettes/", "/").lstrip("./")

tests/llm_translation/test_vcr_redis_persister.py

@@ -81,6 +81,31 @@ def test_redis_key_normalizes_path_passed_by_pytest_recording():
     )
 
 
+def test_redis_key_is_stable_across_working_directories(tmp_path, monkeypatch):
+    repo_root = os.path.dirname(
+        os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+    )
+    abs_cassette = os.path.join(
+        repo_root,
+        "tests/llm_translation/cassettes/test_anthropic/test_streaming.yaml",
+    )
+
+    monkeypatch.chdir(repo_root)
+    key_from_root = redis_key_for(abs_cassette)
+
+    monkeypatch.chdir(os.path.join(repo_root, "tests", "llm_translation"))
+    key_from_subdir = redis_key_for(abs_cassette)
+
+    monkeypatch.chdir(tmp_path)
+    key_from_tmp = redis_key_for(abs_cassette)
+
+    assert key_from_root == key_from_subdir == key_from_tmp
+    assert (
+        key_from_root
+        == "litellm:vcr:cassette:tests/llm_translation/test_anthropic/test_streaming"
+    )
+
+
 class _FlakyRedis:
     def __init__(self, inner, fail_on: str):
         self._inner = inner