CREATE TABLE audit_log (
  id          bigserial PRIMARY KEY,
  actor_kind  text NOT NULL CHECK (actor_kind IN ('user','agent','cron','worker','system')),
  actor_id    uuid,
  entity_type text NOT NULL,
  entity_id   uuid,
  action      text NOT NULL CHECK (action IN ('create','update','delete','suggest','approve','reject')),
  diff        jsonb,
  occurred_at timestamptz NOT NULL DEFAULT now()
);

CREATE TABLE pending_changes (
  id          uuid PRIMARY KEY DEFAULT gen_random_uuid(),
  agent_id    uuid NOT NULL REFERENCES agents(id) ON DELETE CASCADE,
  entity_type text NOT NULL,
  entity_id   uuid,
  action      text NOT NULL CHECK (action IN ('create','update','delete')),
  payload     jsonb NOT NULL,
  reason      text,
  status      text NOT NULL DEFAULT 'pending'
              CHECK (status IN ('pending','approved','rejected')),
  resolved_at timestamptz,
  resolved_by text,
  created_at  timestamptz NOT NULL DEFAULT now()
);

CREATE INDEX idx_audit_entity ON audit_log(entity_type, entity_id, occurred_at);
CREATE INDEX idx_audit_actor ON audit_log(actor_kind, actor_id, occurred_at);
CREATE INDEX idx_pending_status ON pending_changes(status, created_at)
  WHERE status='pending';