The followup runner (used for queued messages, inter-agent sends,
heartbeat followups, etc.) only called typing.markRunComplete() in
its finally block. The typing controller requires BOTH markRunComplete
AND markDispatchIdle to trigger cleanup — but markDispatchIdle was
only wired through the buffered dispatcher path, which followup turns
bypass entirely.
This caused the typing indicator to persist indefinitely on channels
like Telegram when the agent replied with NO_REPLY or produced empty
payloads, because the keepalive loop was never stopped.
Adds markDispatchIdle() alongside markRunComplete() in the followup
runner's finally block, and four test cases covering NO_REPLY, empty
payloads, agent errors, and successful delivery.
Complements #26295 which addressed the channel-level callback layer.
Fixes#26595
Co-authored-by: Samantha <samantha@Samanthas-Mac-mini.local>
6fb082e131