# Control Event Q&A Completeness

<!-- auto-oncall-optimization-record
{
  "schemaVersion": "auto-oncall-optimization-record-v1",
  "optimizationId": "control-event-qa-completeness-2026-07-23",
  "problems": [
    {
      "problemId": "control-event-answer-omits-control-boundaries",
      "summary": "A product-behavior answer can explain a recurring control event correctly while omitting whether it can be disabled independently, whether its frequency is configurable, the side effects of disabling the parent feature, and the least disruptive handling path.",
      "status": "optimized_verified",
      "issueKeys": ["ST-2835"],
      "sourceRefs": ["https://tidb.atlassian.net/browse/ST-2835#problem:qa-control-boundaries-incomplete"],
      "signalTextIncludesAny": ["不支持单独关掉watermarkTs", "没有能降低频率的选项", "下游消费端按 type==TIDB_WATERMARK 直接跳过"],
      "observedThrough": "2026-07-23",
      "effectiveAt": "2026-07-23T05:58:58Z",
      "verifiedAt": "2026-07-23T06:07:57Z",
      "attemptedAction": "Require recurring control-event Q&A to cover event meaning, independent control and frequency boundaries, parent-feature side effects, and the least disruptive handling path; add the established TiCDC Canal-JSON WATERMARK boundary.",
      "evidenceUrl": "https://tidb.atlassian.net/rest/servicedeskapi/request/7911726/comment/23259827"
    }
  ]
}
-->

- Optimization ID: `control-event-qa-completeness-2026-07-23`
- Owner: Codex implementation requested on 2026-07-23
- Source reference: ST-2835 historical AI-versus-human comparison
- Implementation status: merged and deployed to staging
- Effective status: `optimized_verified`

## Bounded problem

The ST-2835 AI draft correctly explained that `TIDB_WATERMARK` is a TiCDC
progress event rather than business data. The later human answer was more
complete because it also established that WATERMARK cannot be disabled alone,
its frequency cannot be reduced, disabling `enable-tidb-extension` removes all
TiDB extension fields, and consumer-side filtering is the least disruptive
default.

## Intended change

Make control-event answers complete across four reusable dimensions: why the
event exists, whether event-only or frequency controls exist, what disabling
the parent feature removes, and which handling path has the least impact. Keep
claims evidence-bound and add the established TiCDC Canal-JSON WATERMARK
boundary to the support reply skill.

## Verification

- Focused contract tests and the complete repository test suite passed
  (406/406).
- The change was merged in `tidbcloud/aisupport#466` at revision
  `80581d6c930a3c16aa3353ba4ebd3fe4551d22bc` and deployed through
  `tidbcloud/app-delivery#75242`.
- The staging Deployment reached 1/1 Ready on the merged image. The live pod
  started at 2026-07-23T05:58:58Z and `/readyz` returned HTTP 200.
- Historical-cutoff read replay
  `6b679786-e832-493d-a03a-f18ea62100f4` and write replay
  `e8d5479c-8e58-4680-a87e-31e6ffcad601` both produced a complete answer:
  WATERMARK is a progress/control event, there is no supported WATERMARK-only
  disable switch, its frequency is not configurable, disabling
  `enable-tidb-extension` removes all TiDB extension fields, and consumer-side
  filtering is the least disruptive default.
- Write replay DB run `60100` updated the existing Jira internal comment
  `23259827` through idempotency key `auto-live:v1:ST-2835:initial`. Jira API
  readback confirmed the same comment ID and `public=false`; no duplicate
  comment was created.

## Unresolved gaps

- This record verifies answer completeness only. It does not authorize a
  customer-visible reply or broader customer-reply rollout.
- The customer-reply validator was not stable enough for opening: it allowed
  one post-change candidate at confidence 0.97 and denied the write-replay
  candidate at confidence 0.98. The latest result therefore remains
  fail-closed even though the answer-completeness criterion passed.

## Next validation action

Use the Q&A opening baseline to collect a larger fixed corpus and make the
publication validator reproducible before any label-based customer-visible
pilot. Keep customer reply disabled until those separate opening criteria pass
and an explicit cutover is approved.