fix(harbor): reject invalid aggregate_attempts values at construction

Only the exact string 'mean' switches collation to mean-of-k; any other
value silently fell through to best-of-k, so a config typo ('Mean',
'avg') would run an experiment with inflated pass@k scores while looking
de-noised. HarborConfig now raises at construction, which surfaces the
mistake at sidecar startup instead of after the trial's budget is spent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: shehabyasser-scale

vero/src/vero/harbor/config.py

@@ -32,6 +32,15 @@ class HarborConfig:
     aggregate_attempts: str = "best"
     extra_args: list[str] = field(default_factory=list)  # passthrough harbor run flags
 
+    def __post_init__(self) -> None:
+        # Only the exact string "mean" activates de-noising; without this check a
+        # typo ("Mean", "avg") would silently run best-of-k with inflated scores.
+        if self.aggregate_attempts not in ("best", "mean"):
+            raise ValueError(
+                f"aggregate_attempts must be 'best' or 'mean', got "
+                f"{self.aggregate_attempts!r}"
+            )
+
     @property
     def is_registry(self) -> bool:
         """Local if the source resolves to an existing path; otherwise a registry ref."""

vero/tests/test_harbor_runner.py

@@ -362,3 +362,24 @@ def test_default_best_unchanged(self, tmp_path):
             0, "t0", _params(),
         )
         assert r.score == 1.0
+
+
+class TestAggregateAttemptsValidation:
+    """A mistyped aggregate_attempts value must fail loudly at construction:
+    only the exact string 'mean' activates de-noising, so 'Mean'/'avg' would
+    otherwise silently run inflated best-of-k."""
+
+    def test_invalid_value_raises(self):
+        with pytest.raises(ValueError, match="aggregate_attempts"):
+            HarborConfig(
+                task_source="org/ds", agent_import_path="p:m",
+                aggregate_attempts="Mean",
+            )
+
+    def test_valid_values_accepted(self):
+        for value in ("best", "mean"):
+            cfg = HarborConfig(
+                task_source="org/ds", agent_import_path="p:m",
+                aggregate_attempts=value,
+            )
+            assert cfg.aggregate_attempts == value