* perf: move complete session-list reads off the event loop
Read persisted compact subagent metadata through the existing read-only
shared-state worker and cooperatively group complete topology with the
session-list work budget.
Share pending fills and fallback results for current waiters, retain exact
local changes, and fence obsolete owners without changing the 500 ms
freshness policy or the remaining synchronous readers.
* fix(sessions): preserve registry publication during read retirement
Keep completed and best-effort registry publication independent of new read admission while retaining strict write and read refusals. Move shared read shapes into leaf type contracts, migrate their consumers, and update the affected fixtures without changing persisted fields.
* test: use the leaf terminal reply type in announce coverage