corpus(models): AuditReport.timestamp is timezone-naive (inconsistent)

[himanshu231204]

Description

The AuditReport model in models.py uses datetime.now() (timezone-naive) as the default factory for the timestamp field:

timestamp: datetime = Field(default_factory=datetime.now)

Meanwhile, the StalenessDetector in staleness.py consistently uses datetime.now(timezone.utc) (timezone-aware) for all its comparisons and metadata. This creates an inconsistency:

• If any code compares report.timestamp with timezone-aware datetimes, it will get a TypeError.
• The timestamp doesn't carry timezone information, making it ambiguous (is it UTC? local time?).
• This is inconsistent with the rest of the corpus module conventions.

Severity

Medium — Not a crash in normal usage (the timestamp field isn't compared in the current tests), but an inconsistency that creates a latent bug for any future code that compares report timestamps with staleness timestamps.

Affected Code

• openagent_eval/corpus/models.py line 71: datetime.now without timezone

Suggested Fix

timestamp: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))