fix(scorer): admit None in list-valued Score so NaN survives event logging (#4491)

[Anai-Guo]

Summary

Fixes #4491. A scorer that returns a list-valued Score containing NaN (e.g. Score(value=[float("nan"), 1.0])) crashes the run at end-of-eval sample logging, finishing with status="error" and no results — an opaque wall of pydantic union errors. The identical value as a dict ({"a": float("nan"), "b": 1.0}) works fine.

Root cause

The two container branches of Value in scorer/_metric.py are asymmetric:

Value = Union[
    str | int | float | bool,
    Sequence[str | int | float | bool],          # <- no None
    Mapping[str, str | int | float | bool | None],  # <- has None
]

Pydantic serializes NaN to JSON null for root, dict, and list placements. On its way into the streaming sample buffer a ScoreEvent is serialized, so [nan, 1.0] becomes [null, 1.0]. When the completed sample is materialized for logging, validate_events re-validates the buffered dicts; the Sequence branch rejects the null, and since the failing event is tried against all event types in the union it surfaces as ~75 unrelated-looking errors. The Mapping branch already admits None, which is why the dict shape survives the same round-trip.

Fix

Align the Sequence branch with the Mapping branch so the NaN → null round-trip is lossy-but-stable, matching what the dict shape already does and the sanctioned NaN-at-root sentinel from #3796:

    Sequence[str | int | float | bool | None],

One-line, symmetric, no behavior change for non-NaN values.

Test

Added test_list_score_with_nan_logs_without_error in tests/scorer/test_metric.py, mirroring the issue's reproduction: a list-valued scorer returning [nan, 1.0] now completes with status="success" and non-None results.

🤖 Generated with Claude Code

[Anai-Guo]

Pushed the regenerated inspect-openapi.json (added null to the Score.value/EvalSampleScore.value/ScoreEdit.value sequence branch), so the check_openapi_drift.py step is now in sync with the Python Value type.

The remaining check-schema-and-types diff is the generated TypeScript (packages/inspect-common/src/types/generated.ts), which lives in the pinned meridianlabs-ai/ts-mono submodule — I can't push there from a fork. It just needs a pnpm --filter @tsmono/inspect-common types:generate + submodule bump on your side to pick up the nullable list item. Happy to adjust if you'd prefer a different approach.