Event keys zero-pad seq to six digits, so an exclusive end bound past
MAX_EVENT_SEQ formatted as a seven-digit prefix that sorts before real
event keys, producing an inverted scan range. This made the newest page
come back empty once a run reached MAX_EVENT_SEQ, and let a client
supplied before_seq beyond MAX_EVENT_SEQ garble the range. Clamp the
bound and treat anything past MAX_EVENT_SEQ as unbounded; no stored
sequence exceeds it, so the results are equivalent.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>