A corrupt import is stored as it came, and "2026-13-01" passed the
pattern, then threw in periodOf on every render. "2026-02-30" rolled into
March instead and moved the cycle. The schema now round-trips the date,
so either is kept on disk and left off screen like any unreadable task.
Found by the schema-guardian review.
Co-Authored-By: Claude Opus 5.5 <[email protected]>