The 'failing source degrades to perSource error' test hardcoded
DTSTART:20261007T100000Z. The /events route defaults to a
now-7d..now+30d window, so the fixture silently expired on 2026-10-14
and this was the single failing test in every full-suite run since.
Fixture now builds DTSTART for tomorrow UTC at runtime.
Verified: file suite 15/15; full suite 3704/3705 (this was the only
failure). Judge A — urn:ump:3n5xljspojvc57x7isxi4busps2dxlpwuzivhntg44i3jkpiqfaa