-- Who performed an assignment (terdut-server#35). On an 'assigned' event
-- incident_events.user_id is the assignee, so the actor needs columns of its
-- own. Only populated for 'assigned' events; every other event type keeps
-- using user_id/service_account_id for the actor. Older 'assigned' rows stay
-- NULL (the actor was never recorded). Same shape as migration 015: nullable,
-- mutually exclusive, ON DELETE SET NULL.
--
-- assigned_to_service_account_id is still deliberately not added: making
-- service accounts assignable is a separate change (request body, assignee
-- picker, notifier, filters).
ALTER TABLE incident_events
    ADD COLUMN actor_user_id BIGINT REFERENCES users(id) ON DELETE SET NULL,
    ADD COLUMN actor_service_account_id BIGINT REFERENCES service_accounts(id) ON DELETE SET NULL;

ALTER TABLE incident_events
    ADD CONSTRAINT incident_events_assign_actor_xor_chk CHECK (
        actor_user_id IS NULL OR actor_service_account_id IS NULL
    );

CREATE INDEX incident_events_actor_user_id_idx ON incident_events(actor_user_id);
CREATE INDEX incident_events_actor_service_account_id_idx ON incident_events(actor_service_account_id);