pub fn resolve_shared_reactive_dir() -> Option<PathBuf>Expand description
Resolve the GLOBAL <home>/shared/agents/reactive/ directory — the
cross-channel presence registry for live reactive-injection targets
(agent_id -> local_url/block_id/pid/auth_key, one entry per channel),
used by MuxBus Tier 2b same-host cross-channel delivery
(issue #1916 / PR #2350) and by agent admission’s other-instance probe.
Sibling of resolve_shared_registry_dir in location (both live
under shared/agents/), but a different concern: that registry
mirrors durable agent definitions/session-resume state, while this one
tracks live, ephemeral reachability for message forwarding — entries
here are written at reactive-register time and removed at unregister;
any a crashed channel leaves behind are dropped by the startup sweep.
Returns None only if the global shared root can’t be resolved —
caller treats this as “cross-channel delivery disabled,” falling back
to same-channel-only Tier 2 (no behavior regression).