The six cases the issue names, plus the boundary (the grace is inclusive), a
verdict inside the window against an old head, both unreadable timestamps, and
the configured-grace override.
Two proofs run rather than asserted in prose: a copy of the script with the
gate removed must flag the PENDING fixture, and a copy with the grace removed
must flag the inside-the-window one. The harness checks itself against the
unmutated copy first, or a flip would prove nothing.
The pre-#236 stall fixtures gain real timestamps. Their symbolic stamps are
not unreadable — GNU date reads `t1` as 01:00 in military timezone T, a time on
whatever day the suite runs — so a grace measured against a fixed NOW would
flip with the calendar. Every assertion is byte-identical.
Refs #236
