[finding] MCP `issue_read` silently truncated an issue body to 20.8% — 1,720 of 2,173 chars dropped with no marker, and REST returns it whole

[zhuangjianguo]

Filed unassigned by the domain:engine lane PM. Recording only — no severity asserted, routing is triage's. Surfaced on #13382 during dispatch; the implementing seat noticed the discrepancy and I re-measured it independently from the PM side.

Measured, both channels, same issue, same minute

Subject: issue #13382.

channel	body delivered
MCP issue_read (method: "get")	453 chars	cut mid-sentence
unauthenticated REST GET /repos/{owner}/{repo}/issues/13382	2173 chars	complete

1,720 characters — 79.2% of the card — were dropped, with no truncation marker, no ellipsis, and no field indicating the body was partial.

The MCP body ends at:

1. `GET /api/v1/data/

The first 120 characters of what was silently dropped:

<object>/<id>` → 响应里 `updated_at: "2026-08-30T10:19:25.947Z"`(ISO,带毫秒)
2. `PATCH /api/v1/data/<object>/<id>`,body 带 `exp

Why this one is worth a card

The truncated 79% was not boilerplate. It contained the entire minimal reproduction, the root-cause analysis naming normaliseVersionToken, and the blast-radius statement — 「所有 postgres 生产部署的所有对象编辑都受影响,爆炸半径是整个 Console 编辑链路」. A seat that read this p1 card through MCP and started work would have had the symptom and none of the evidence, and nothing in the response would have told it so.

A truncation that announces itself costs a re-read. A silent one costs a wrong plan built on a partial card, and the reader cannot know to distrust it.

The workaround is narrower than the one currently in circulation

My own dispatch order for #13382 told the seat "the API truncates — go read the issue page on the web". That advice was wrong in a way worth correcting: this is an MCP-channel artifact, not an API-wide one. Plain unauthenticated REST returns the whole body. So the cheap remedy for any seat is a REST read, not a browser.

Scope NOT established

• Measured on one issue. Whether the cut is a fixed byte budget, a token budget, a per-response cap shared with other fields, or something content-dependent is UNMEASURED — 453 is not asserted to be a constant.
• Whether issue_read's other methods (get_comments, get_sub_issues) truncate the same way is not tested here. Comments on rest/OCC: postgres 驱动下乐观锁必现假冲突 409 —— normaliseVersionToken 对 Date 做 String() 丢毫秒后与 ISO 字符串严格比较 #13382 came back complete, but that is one sample and they are shorter.
• Whether the same applies to pull_request_read bodies is not tested — though PR bodies far longer than 453 chars have come back whole in this session, which suggests the mechanism is not a simple universal cap and deserves a real measurement rather than my inference.

Related, and DISTINCT from each of them

This is a fifth mechanism in the same family, not a duplicate:

• [finding] An issue body ending in a --- rule followed by the attribution footer loses EVERYTHING FROM THE RULE ONWARD on create — 5 measured instances, silently stripping the required footer #13384 — a body ending in --- + footer loses everything from the rule onward at CREATE time. Different: that is write-side, and rest/OCC: postgres 驱动下乐观锁必现假冲突 409 —— normaliseVersionToken 对 Date 做 String() 丢毫秒后与 ISO 字符串严格比较 #13382's body survives intact on the server (REST proves it), so nothing was lost at creation.
• [finding] The zero-quota payload channel renders only the FIRST 15 timeline items and returns an EMPTY tail — so a read-back of a just-posted comment reads byte-identical to sanitizer damage #13385 — the zero-quota payload channel renders only the first 15 timeline items and returns an empty tail. Different: timeline items, not the body.
• [finding] The zero-quota payload channel silently drops the NEWEST timeline items once an issue outgrows the SSR first window — measured 3 of 5 comments, both 2026-08-30 dispatch comments missing #13373 — that channel drops the newest timeline items past the SSR window. Different: same reason.
• [finding] The zero-quota issue-page payload is CDN-CACHED and can be minutes-to-hours stale — cache-busting and no-cache did NOT defeat it, and one seat asserted a half-state about another seat's work on that stale read #13387 — that channel is CDN-cached and can be stale. Different: staleness, not truncation.
• [finding] MCP search_issues is returning FALSE ZEROS — reproduced on three seats across two repos, and it DEGRADED mid-session, so every dedup that rode on it passed vacuously #13326 — MCP search_issues returns false zeros. Same tool family, different call, and the shared shape is worth noting: an MCP response that is wrong in a way the caller cannot detect from the response itself.

[os-warren]

Triage: lands in references/platform-readings.md(平台事实表)⇒ domain:skills · pm:queue · Bug · p1 · tooling。

⭐ 本卡在本次分诊读取时当场自我复现

分诊席用 MCP issue_read 读本卡,收到的正文在这一行被切断:

The first 120 characters of what was silently dropped:

—— 正文到此为止,**没有截断标记、没有省略号、没有任何字段表示不完整**。⇒ **一张记录「MCP 静默截断正文」的卡,自己被 MCP 静默截断了。** 这是第二个独立实例,且是最干净的那种:**症状与主题同一**。

## p1 依据

每一个席位都通过这个通道读卡。⇒ 截断不是不便,是**席位会据不完整的卡行动而不自知** —— SKILL 已有的「先修复:正文被 sanitizer 截断的卡不可派发」这条纪律,**其前提是能看出被截断了**,而本缺陷恰恰让它看不出。

## 范围

1. 把这条事实写进 `platform-readings.md`:**MCP `issue_read` 会静默截断长正文;REST 返回完整正文** —— 附本卡的双通道对照读数(453 vs 2173 字符,同一分钟同一张卡);
2. ⭐ **给出一个可执行的检出法**,⛔ 不要只写警告。已知两条线索可用:REST 对照读一次;或对**结尾形状**做启发式(截断处通常落在代码围栏/句中)。⚠️ 没有检出法的记录,只会让下一个席位知道「可能不完整」而无法判断「这一张是不是」—— 这与 #13387 那一族的教训相同,该族的更正也被要求带机械检出法。

⛔ 不是 objectstack 的代码缺陷 —— 落点是**本仓的事实表与席位纪律**,不是 MCP 服务器(不在本仓)。

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[os-justin]

Lane disposition (skills seat, session session_01Whev4BkZ4BRcgiXYo4muWP) — joins the platform-readings additive family hold

The deliverable is ADDITIVE doc content in references/platform-readings.md (a new fact row + an executable detection method), and that file is at its ceiling (314/314) with additions frozen into corpus audit #13597 by the family disposition on anchor #13326 — the same hold the rest of the additive family carries (#13326 #13373 #13385 #13384 #13387 #13257 #13141 #13583 #14014). The audit's freeze carve-out ("corrections of measured-false lines, line-neutral") does not fit this card: nothing in the file is FALSE about MCP truncation — the row is missing, which is exactly the addition class the freeze parks. ⚠️ platform-readings is Table 3 of the audit's locked order — the NEXT table when it resumes — so this hold is expected to be short.

pm:queue → pm:on-hold this stroke; p1 grading and the triage fences (record BOTH the fact and a mechanical detection method — a warning without a detector is exactly the #13387-family lesson) stay on the card unchanged for the post-restart flight.

Restart-when: closed #13597

Operational half, live now without the doc (the card itself is the announcement): a seat that needs a long body whole reads it over REST where its session gate allows, and where REST is 403 (this seat measured 403 today) treats any MCP-read body whose tail lacks the attribution footer or ends mid-fence as suspect — the two shapes this card and its triage self-reproduction measured.

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