feat: F5.6c measured and accepted on test-filius; tickets up to 5 s ahead of F's clock

test-filius refused every ticket as from the future: its clock was 886 ms
behind the dashboard's machine, with NTP still 8 ms (one ticket in 125, as a
ticket carries whole seconds). F now takes a ticket signed up to 5 s ahead
(TICKET_AHEAD_SECONDS); itsdangerous refuses one second, and the oracle
keeps that on record.

tools/live measures and accepts on a live F, with fresh projects each run:
m3 (200 rooms of the largest example with pings: probe p95 37 ms), m4 (63 KB
document; dragging makes an update per pointer move, 59/s), m5 (an hour
through the proxy), acceptance (two browsers, 14 checks, passed three times)
and clock (F's clock against ours).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/ticket-oracle/tickets.py

@@ -64,6 +64,8 @@ def main(out):
         ("sixtySecondsOld", plain, SIGNED_AT + 60),
         ("sixtyOneSecondsOld", plain, SIGNED_AT + 61),
         ("fromTheFuture", plain, SIGNED_AT - 1),
+        ("fiveSecondsAhead", plain, SIGNED_AT - 5),
+        ("sixSecondsAhead", plain, SIGNED_AT - 6),
         ("otherSecret", sign(claims(), secret="another-secret"), SIGNED_AT),
         ("scratchSalt", sign(claims(), salt="mdg-scratch-ticket"), SIGNED_AT),
         ("tamperedPayload", tampered(plain), SIGNED_AT),