Lifecycle

constructor      bb_bus_open → bb_register_instance → bb_add_output / bb_add_input
restore state    bb_set_instance_uid(saved uid) → bb_load_connections(saved text)
audio callback   bb_begin_block → bb_read_input … bb_write_output → bb_end_block
save state       bb_endpoint_uid → bb_save_connections
UI / timer       bb_list_outputs (source menus), bb_connect / bb_disconnect,
                 bb_endpoint_patch_version (mark the set dirty)
destructor       bb_unregister_instance → bb_bus_close

Rules:

1. Register in the constructor with UID 0 (a fresh UID), so the instance is on the bus before the host restores its state.
2. When the host restores state, call bb_set_instance_uid with the saved UID. If it returns BB_ERR_UID_IN_USE, the user duplicated the device: keep the fresh UID, and still load the saved cables.
3. Add all inputs before bb_load_connections.
4. Save bb_endpoint_uid (not the UID you asked for) and the bb_save_connections text in your plugin state.
5. Poll bb_endpoint_patch_version on the message thread a few times per second. When it changes, tell the host your state changed. In JUCE: updateHostDisplay(ChangeDetails().withNonParameterStateChanged(true)).
6. Unregister before closing the bus.