# 다이제스트가 덮던 다섯 성분과 그때 같아지던 쌍
 * <p>It omitted several. {@code transition|operationId|ownerToken|attempt|stateRevision} covers who
 * and when, and nothing about what: a {@code FAIL} recorded with a retryable disposition and one
 * recorded as abandoned produced identical digests, as did two completions carrying different
 * responses or different retention. A replay comparing digests concluded "same transition" for two
 * transitions whose whole difference was the part that mattered.
 *
 * <p>Length-framed, because every component is variable-width text and at least one — the owner
 * token — is not this platform's to constrain. Joining with a delimiter means two different
 * component lists can render to one string.
 */

# 지금 각 호출부가 실제로 넘기는 의미 인자
181:    String startDigest = transitionDigest("START", operationId, owner);
220:        transitionDigest("RENEW", operationId, owner, Long.toString(processingLeaseTtl.toMillis()));
365:    String releaseDigest = transitionDigest("RELEASE", operationId, owner);
            transitionDigest(
                "COMPLETE",
                operationId,
                owner,
                responseDigest,
                Long.toString(replayTtl.toMillis())),
            response.payload(),
    String transitionKind =
        disposition == IdempotencyFailureDisposition.NO_EFFECT_RETRYABLE
            ? "FAIL_RETRYABLE"
            : "FAIL_ABANDONED";
    String failDigest =
        transitionDigest(
            transitionKind,
            operationId,
            owner,
            disposition.name(),
            Long.toString(retention.toMillis()));

# 이어 붙일 때 각 성분 앞에 적는 길이와, 해시가 실제로 먹는 바이트
  private static void write(StringBuilder out, String value) {
    out.append(value.length()).append(':').append(value);
79:              MessageDigest.getInstance("SHA-256").digest(value.getBytes(StandardCharsets.UTF_8)));
30:  static final int VERSION = 2;
59:    write(framed, "v" + VERSION);

# 그런데 완료 재생 분기는 이 다이제스트를 비교하지 않는다
    if (row.state() == IdempotencyState.COMPLETED
        && "COMPLETE".equals(row.lastTransitionKind())
        && operationId.value().equals(row.lastTransitionOperationId())) {
      return responseDigest.equals(row.responseDigest())
          ? IdempotencyCompleteOutcome.ALREADY_COMPLETED_SAME_RESULT
          : IdempotencyCompleteOutcome.RESPONSE_CONFLICT;