Share one bind helper across the runs insert/upsert/update statements,
compute the next event sequence once per append, and decode stored
sequence columns through a single helper. Check the run head before
decoding events, rewrite the first-visit stage listing as a UNION ALL so
each arm uses its partial index, and share the run_events insert SQL
with the test seeder.
Collapse the duplicated in-memory pool fixture, remove two tests that
only asserted Arc sharing, and fold the fabro-db test row helpers.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
ff2aef4564