The previous fix (cancel_all_write_response_handlers in do_drain)
was too aggressive — it killed all handlers including ones used by
group0 for raft commits. Since group0 is still running at that point
(before wait_for_group0_stop), this caused group0 operations to fail
(SCYLLADB-2168).
The actual problem is only with handlers that have pending remote
targets: after stop_transport() their MUTATION_DONE responses can
never arrive via messaging. Handlers whose only pending targets are
local can still complete via apply_locally and should be left alone.
Add cancel_nonlocal_write_response_handlers() which checks each
handler's remaining targets against the local host ID. Only handlers
with at least one remote pending target are cancelled. Use it in
do_drain instead of cancel_all_write_response_handlers. The latter
remains unchanged for drain_on_shutdown (final proxy shutdown where
all handlers must be killed).
Fixes: SCYLLADB-2168
Closesscylladb/scylladb#30020
954426407e