fn notify_tracked_blocks_changed()Expand description
Announce a CONTROLLER_REGISTRY membership change to the Process Broker,
if one is running (never set in most unit tests). See
ProcessBroker::emit_tracked_blocks_changed’s doc comment for why this
exists: agent.tracked-blocks reads this registry directly, but nothing
used to tell a subscriber when a write here changed what that read would
return — Swarm’s client-side list depended on two unrelated, independently-
timed events instead, and went stale whenever neither happened to fire for
a given block. See docs/reports/REPORT_SWARM_MOUNT_DEPENDENT_TRACKING_GAP_2026_09_15.md.