docs(i18n): state the requiredSince grandfather semantics explicitly

Files dated before the cutoff are the grandfathered backlog by
definition (including cutoff-eve creations); backdating is a
review-visible RFC-convention violation, not a loophole.

docs/i18n/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-README.md: ba3431c72d9f2a86220df4ed682620514401291f
-README.zh.md: 02957c97937525a1da27242620a8327b863de040
+README.md: bbf292893fc1ca634f3437a8ea0bae855c5712cb
+README.zh.md: 29f7408d1e0511ebf5a708507e0ea93aeb7e9ff3

docs/i18n/README.md

@@ -43,7 +43,7 @@ The gate's limit, stated plainly: **a green gate means the pair was confirmed co
 - `docs/AGENTS.md` — agent instructions, maintained in English only like the root `AGENTS.md`.
 - `docs/i18n/terminology.md` — the terminology table is itself bilingual by construction.
 
-**Rollout**: new documents don't wait for a batch — a date-named document (`yyyy-mm-dd-*.md`, i.e. an RFC) dated on or after the manifest's `requiredSince` cutoff must merge with its pair, so everything new is bilingual from birth. For the back-catalog, the `required` list in the manifest is the enforcement frontier, not the goal. The goal is full bilingual coverage of the scope. Pairs land in reviewable batches (core entry docs, cookbook, RFCs, postmortems, …); each merged batch adds its files to `required`, so the gate ratchets forward and never regresses. Documents not yet in `required` are backlog — visible in `--list` — but any pair that already exists is held to the full contract regardless of the list. Pairing a document is a commitment: every later edit to either side must carry the counterpart along, so grow the frontier at the pace translation review is actually resourced, not ahead of it.
+**Rollout**: new documents don't wait for a batch — a date-named document (`yyyy-mm-dd-*.md`, i.e. an RFC) dated on or after the manifest's `requiredSince` cutoff must merge with its pair, so everything new is bilingual from birth. Files dated before the cutoff are the grandfathered backlog by definition — including files created on the cutoff's eve — and a document's filename date is its first-proposed date per the RFC convention, so backdating past the cutoff is a review-visible violation, not a loophole. For the back-catalog, the `required` list in the manifest is the enforcement frontier, not the goal. The goal is full bilingual coverage of the scope. Pairs land in reviewable batches (core entry docs, cookbook, RFCs, postmortems, …); each merged batch adds its files to `required`, so the gate ratchets forward and never regresses. Documents not yet in `required` are backlog — visible in `--list` — but any pair that already exists is held to the full contract regardless of the list. Pairing a document is a commitment: every later edit to either side must carry the counterpart along, so grow the frontier at the pace translation review is actually resourced, not ahead of it.
 
 ## Division of labor
 

docs/i18n/README.zh.md

@@ -43,7 +43,7 @@
 - `docs/AGENTS.md`——agent 指令，与根 `AGENTS.md` 一样只以英文维护。
 - `docs/i18n/terminology.md`——术语表本身即是双语构造。
 
-**推进**：新文档不等批次——文件名带日期的文档（`yyyy-mm-dd-*.md`，即 RFC）日期在 manifest 的 `requiredSince` 当天或之后，就必须连同配对一起合入，新增的一切生来即是双语。对于存量文档，manifest 中的 `required` 列表是强制边界，不是目标。目标是范围内的全量双语覆盖。配对按可评审的批次落地（核心入口文档、cookbook、RFC、postmortem……）；每个批次合入后把其文件加进 `required`，门禁只进不退。尚未进入 `required` 的文档是 backlog——在 `--list` 中可见——但任何已存在的配对无论在不在清单里都按完整契约检查。给一篇文档配对是一份承诺：此后对任一侧的每次修改都必须带上另一侧，所以边界的扩张要跟上翻译评审的实际投入节奏，不要抢在前面。
+**推进**：新文档不等批次——文件名带日期的文档（`yyyy-mm-dd-*.md`，即 RFC）日期在 manifest 的 `requiredSince` 当天或之后，就必须连同配对一起合入，新增的一切生来即是双语。日期早于 cutoff 的文件按定义属于被豁免的存量——包括 cutoff 前夜创建的文件——而文件名日期按 RFC 惯例即首次提出日期，倒填日期绕过 cutoff 是评审可见的违规，不是漏洞。对于存量文档，manifest 中的 `required` 列表是强制边界，不是目标。目标是范围内的全量双语覆盖。配对按可评审的批次落地（核心入口文档、cookbook、RFC、postmortem……）；每个批次合入后把其文件加进 `required`，门禁只进不退。尚未进入 `required` 的文档是 backlog——在 `--list` 中可见——但任何已存在的配对无论在不在清单里都按完整契约检查。给一篇文档配对是一份承诺：此后对任一侧的每次修改都必须带上另一侧，所以边界的扩张要跟上翻译评审的实际投入节奏，不要抢在前面。
 
 ## 分工