Tell a running daemon to drop its in-memory read cache (SessionCache).
Returns true if a daemon was reached. Never auto-starts a daemon — if none
is running there is no cache to flush. Force-rebuild CLI commands call this so
ctx_read map/signatures stop serving pre-rebuild output from the daemon’s
long-lived cache, which CLI index rebuilds otherwise can’t reach (#420).
Check the daemon’s cross-agent delivery registry for a content hash.
Returns None if daemon unreachable or no hit. Connect-only — never
auto-starts a daemon (delivery is best-effort).