origin_session_id (the api_server wake self-post target) lived only in
the in-memory record: durable dispatch persistence and abandoned-
delegation recovery omitted it, leaving completions recovered after a
process restart unroutable to api_server sessions. Persist it in the
async_delegations table (CREATE TABLE + ALTER TABLE migration for legacy
DBs), restore it on recovery, and expose it via get_durable_delegation.
Also adds the contributors mapping for ianks (PR #64998 author).
Follow-up to #64998 (sweeper review F3).
