If start_server_for_group0() successfully registers a server in
_raft_gr._servers but a subsequent step (e.g. enable_in_memory_state_machine())
throws, the server is never destroyed because abort_and_drain()/destroy()
check std::get_if<raft::group_id>(&_group0) which was only set after the
entire with_scheduling_group block completed.
Move _group0.emplace<raft::group_id>() inside the lambda, immediately after
start_server_for_group() succeeds, so that cleanup paths can always find
and destroy the registered server.
This fixes the assertion:
"raft_group_registry - stop(): server for group ... is not destroyed"
which manifests during shutdown after an upgrade where topology_state_load()
fails due to netw::unknown_address.
Backport: Yes, to 2026.1, 2026.2, as it causes a crash on upgrades
Refs: SCYLLADB-1217
Refs: CUSTOMER-340
Refs: CUSTOMER-335
Fixes: SCYLLADB-1801
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
AI-assisted: Yes, Opencode/Opus 4.6
Closesscylladb/scylladb#29702
6179406467