wlr_swapchain_acquire() returns a locked buffer and
wlr_output_state_set_buffer() takes its own lock, so every output enabled
through output management (wlr-randr, kanshi) leaked a buffer. Unlock it
once the state holds it, as wlr_output_swapchain_manager does.
When the session goes away, e.g. seatd being stopped at shutdown, wlroots
destroys the backend by itself (wlr_auto_backend_monitor), and
wlr_backend_finish() aborts since dwl's new_output and new_input listeners
are still attached:
Assertion failed: wl_list_empty(&backend->events.new_input.listener_list)
Detach them and quit instead.
dvh