fix(drift): probe-failure also flags a missing baseline fingerprint (#188 review)

Copilot (PR #188) noted that the probe-first ordering introduced in #186
means a probe_failed early-return no longer mentions a missing expected
fingerprint: if the probe raises AND no baseline is committed, only the probe
error surfaced, masking the missing-baseline config error.

Route both probe-failure paths through a _probe_failed() helper that appends
"expected fingerprint is missing at <path>" when the baseline file is absent,
while preserving the underlying probe error. No change when a baseline exists.

+ regression test (probe raises + no baseline -> error mentions both).

Author: enriquea

hvantk/core/plugin/drift_runner.py

@@ -37,6 +37,25 @@ def run_drift_check(dataset_name: str, *, timeout: int = 60) -> DriftResult:
     return _run_drift_check_with_spec(spec, timeout=timeout)
 
 
+def _probe_failed(spec: DatasetSpec, exc: DriftProbeError) -> DriftResult:
+    """Build a probe_failed result, also flagging a missing baseline fingerprint.
+
+    The probe runs before the baseline is read (so intentional stubs classify
+    correctly). Without this, a plugin whose probe fails AND ships no committed
+    baseline would surface only the probe error and silently hide the
+    missing-fingerprint configuration issue. The underlying probe error is
+    preserved either way.
+    """
+    fp_path = Path(spec.test_paths.drift_fingerprint)
+    if not fp_path.exists():
+        exc = DriftProbeError(
+            f"{exc}; additionally, expected fingerprint is missing at {fp_path}"
+        )
+    return DriftResult(
+        dataset_name=spec.name, status="probe_failed", probe_error=exc
+    )
+
+
 def _run_drift_check_with_spec(
     spec: DatasetSpec, *, timeout: int = 60
 ) -> DriftResult:
@@ -47,16 +66,10 @@ def _run_drift_check_with_spec(
     try:
         observed = _invoke_with_timeout(spec.drift_probe, timeout=timeout)
     except DriftProbeError as exc:
-        return DriftResult(
-            dataset_name=spec.name,
-            status="probe_failed",
-            probe_error=exc,
-        )
+        return _probe_failed(spec, exc)
     except Exception as exc:  # noqa: BLE001
-        return DriftResult(
-            dataset_name=spec.name,
-            status="probe_failed",
-            probe_error=DriftProbeError(f"probe raised {type(exc).__name__}: {exc}"),
+        return _probe_failed(
+            spec, DriftProbeError(f"probe raised {type(exc).__name__}: {exc}")
         )
 
     if observed.get("probe_status") == PROBE_STATUS_STUB:

hvantk/tests/test_drift_runner.py

@@ -91,6 +91,24 @@ def boom():
     assert "network down" in str(result.probe_error)
 
 
+def test_probe_failure_with_missing_baseline_reports_both(tmp_path: Path):
+    """When the probe fails AND no baseline fingerprint is committed, the error
+    must surface both the probe failure and the missing-fingerprint path — the
+    probe-first ordering must not mask the missing-baseline config error
+    (PR #188 review: Copilot)."""
+    fp_path = tmp_path / "does-not-exist.json"  # no baseline written
+
+    def boom():
+        raise DriftProbeError("network down")
+
+    spec = _make_spec(probe_return=boom, fingerprint_path=fp_path)
+    result = _run_with_spec(spec)
+    assert result.status == "probe_failed"
+    msg = str(result.probe_error)
+    assert "network down" in msg  # underlying probe error preserved
+    assert "missing" in msg.lower() and str(fp_path) in msg  # baseline flagged
+
+
 def test_fetched_at_is_excluded_from_comparison(tmp_path: Path):
     fp_path = tmp_path / "fp.json"
     _write_fingerprint(