Session-based channel discovery resurrected historical origins for
platforms with no connected adapter, exposing stale send_message
targets that can no longer deliver. Gate both the enum loop and the
plugin-registry loop on the live adapter set.
Surgical reapply of the channel-directory portion of PR #25959 (branch
was 6.5k commits stale; the text-batching delay changes bundled there
were dropped - separate concern, defaults have since been retuned on
main).
Co-authored-by: Marco-Olivier Lavoie <marcolivier@gmail.com>
