Subagent list/tail/steer/interrupt authorized against a per-record copy of
the owning session's transport (`owner_transport`). That copy had to be
re-synced at every reattach site; `_rebind_live_transport` did it for
session.resume/activate but prompt.submit and the queued-prompt drain still
attached bare, so a client that reconnected through a prompt (the common
path on a remote gateway / Bot Mode switch) streamed fine while
`subagent.list` returned [] and controls rejected.
Read `owner_session_record["transport"]` at check time instead: the slot is
already mutated by every attach/detach/viewer-failover path, so no site can
forget the sync. `owner_transport` stays as the capture-time "commissioned
by a gateway session" marker (None = no RPC authority ever); non-dict owners
keep the exact-object rule. Drops the registration-time re-read and the
attach-time registry loop.
Diagnosis credit: nftpoetrist (#106663) — their prompt.submit / drain
regression tests pass against this change with no call-site edits.
Teknium