ALTER TABLE generation_tasks
  ADD COLUMN IF NOT EXISTS task_snapshot JSONB NOT NULL DEFAULT '{}'::jsonb;

CREATE TABLE IF NOT EXISTS task_dispatch_outbox (
  task_id UUID PRIMARY KEY REFERENCES generation_tasks(id) ON DELETE CASCADE,
  status TEXT NOT NULL DEFAULT 'pending'
    CHECK (status IN ('pending', 'leased', 'sent', 'failed')),
  available_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  attempts INTEGER NOT NULL DEFAULT 0,
  lease_owner TEXT,
  lease_expires_at TIMESTAMPTZ,
  last_error TEXT,
  dispatched_at TIMESTAMPTZ,
  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
);

CREATE INDEX IF NOT EXISTS task_dispatch_outbox_poll_idx
  ON task_dispatch_outbox(status, available_at);