sessions and session_defaults are new and append-only. thread_claims, message_threads and
thread_opens are rebuilt in place with a session column, and thread_claims gains a generation
counted from claim rows. Each existing thread gets a default session with the thread's id; new
threads get a random one. Holder, per-run, release and delivery triggers key on the session,
and two id triggers keep session and thread ids apart (Duckworth checks 1-7, duckworth-0106).
The broker binds a thread run to a session (the default when the record names none), and
thread.open, thread.send and thread.messages take an optional session. New verbs session.list
and session.create (idempotent on op). Tests: sessions.test.mjs for T1 bus half, T2 and T7 with
a pinned 3k fixture; count, version and verb pins; hand-made test threads write the legacy
default session.
Built on row 236 (8f51900b5), which takes 3j-3k, so this step is 3k-3l by landing order
(row264 Q2, sage-2412). The op values are legacy-3l and migration-3l. gitea-migration.test reads
its store after both steps. Not run yet: every run waits for Sage's CLEAR.
jason.woltje
d6301dffce