_allow_replay incremented the per-user counter on every
/api/events GET, including no-op connects from a fresh client
with no cursor against an empty backlog. React StrictMode dev
double-mounts plus a few tabs trivially tripped the default
30-per-60s budget on idle reconnects.
XLEN pre-check: when last_event_id is None and the user stream
is empty, the connect can't do snapshot work — return True
without INCR. Cursor-bearing connects still INCR unconditionally
(probing the cursor's relationship to stream contents would
require a redundant XRANGE).
cb3ca8a36b