-- docs/flight-state.md §5 (ACM2-29 P2-3): 提交后共享信箱回填的持久补偿待办。
-- 业务事务已提交（PROC_STATE=SUCCEEDED）后回填失败 → 落本表重试；
-- 回填失败不得把已成功的业务事务重新标记为失败，也不得重放业务变更。

CREATE TABLE IF NOT EXISTS backfill_todo (
  cminmsgs_id     BIGINT       PRIMARY KEY,
  sndr            VARCHAR(64)  NOT NULL,
  type            VARCHAR(32)  NOT NULL,
  styp            VARCHAR(32),
  seqn            BIGINT,
  attempts        INTEGER      NOT NULL DEFAULT 0,
  next_attempt_at TIMESTAMP(6) WITH TIME ZONE NOT NULL,
  last_error      VARCHAR(512),
  created_at      TIMESTAMP(6) WITH TIME ZONE NOT NULL,
  updated_at      TIMESTAMP(6) WITH TIME ZONE NOT NULL
);

CREATE INDEX IF NOT EXISTS idx_backfill_todo_due ON backfill_todo (next_attempt_at);