docs(i18n): state who owns the metadata-form baseline where the gate is taught

`content/docs/ui/translations.mdx` recommends `os i18n check --strict
--threshold` as the CI gate; that advice is now reachable for an app package,
and the page has to say what is and is not in the number it produces —
including why shipping your own `metadataForms` bundle to move it is the wrong
repair.

The published i18n skill listed metadata forms among the surfaces `check`
always reports on. That sentence is false as of this change, so it is
corrected in place rather than left to read as a scope statement.

`content/docs/protocol/kernel/i18n-standard.mdx` names `metadataForms` only in
its ORPHAN-key paragraph (the reverse direction, which `os validate` / `os
lint` / `os compile` answer) — untouched by this change and left alone.

Claude-Session: https://claude.ai/code/session_015QE8qk46e5CHJxyQEUjbf8
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/i18n-check-platform-bucket-and-app-gating.md

@@ -0,0 +1,63 @@
+---
+"@objectstack/cli": minor
+---
+
+fix(cli): `os i18n check` counts the coverage an app actually owns, so `--strict` / `--threshold` can gate an app package (#16681)
+
+## What was wrong
+
+`collectExpectedEntries` walks the Studio metadata-form registries
+unconditionally — identically for every config, an empty one included — so
+every stack's expected set carries ~773 `metadataForms.*` keys that
+`@objectstack/platform-objects` translates and the runtime already serves.
+
+Two of the three commands that see that family already knew it is not the
+author's. `os lint` hides it and says so ("platform built-ins: 773 i18n
+issue(s) hidden — rerun with `--include-platform`"); `os i18n extract` has
+`--no-metadata-forms`. `os i18n check` is the one command that publishes a
+**percentage**, and it carried the baseline in its denominator:
+
+```
+Coverage by locale
+  en       ████████████████████████ 100.0%  (1265/1265, missing 0)
+  zh-CN    █████████░░░░░░░░░░░░░░░  38.9%  (492/1265, missing 773)
+```
+
+That is an application with every key it owns translated. `--strict` and
+`--threshold` — the two flags whose entire purpose is CI gating — therefore
+could not gate an app package at all, and the only way to move the number was
+to ship a copy of the platform's bundle, which would *override* the platform's
+own and go stale at the next upgrade. The workaround was worse than the defect.
+
+## What it does now
+
+**Ownership is observed, not assumed.** The baseline counts toward coverage
+when the stack under examination ships those translations itself, and does not
+when it does not — read from the config's own `translations` bundles, requiring
+a non-empty string leaf so an `--fill=empty` scaffold is not mistaken for a
+claim of ownership. An app gets a number about its own surface with no flag;
+`platform-objects`, which does ship the family, stays gated on it with no flag
+either. An unconditional exclusion would have turned the app side green by
+deleting the platform's own gate, and is what the negative-control tests forbid.
+
+**The flag is `os lint`'s, spelling and all.** `--include-platform` forces the
+baseline in; `--no-include-platform` forces it out, for a package that ships a
+partial baseline and does not intend to own the rest. Absent, the decision is
+the observed one — three states, not two.
+
+**Both output faces carry the decision.** `--json` gains
+`platformMetadataForms: { mode, excludedKeys }`, and the console prints
+`platform built-ins: N key(s) not counted — rerun with --include-platform to
+gate them here` under the coverage table, rendered from those same two numbers.
+
+`os lint` is unchanged. The shared `computeI18nCoverage` seam still counts the
+baseline by default, because lint folds it away one seam later and counts what
+it folded for its own hint line.
+
+## Compatibility
+
+Additive on the command surface; an invocation that was refused is now
+accepted, and no flag is removed or renamed. The behaviour that changes is the
+**default coverage number for a stack that ships no `metadataForms` bundle** —
+it stops reporting a debt that stack must not pay. A run that wants the old
+numbers back asks for them with `--include-platform`, on the same argv.

content/docs/ui/translations.mdx

@@ -244,6 +244,23 @@ A missing string in the **default** locale is an error; missing strings in
 other locales are warnings until you set `--strict` / `--threshold`. The Todo
 example ships a completeness test alongside its bundles — worth copying.
 
+### What counts as *your* coverage
+
+The Studio's own metadata forms (`metadataForms.*` — several hundred keys
+across every metadata type) are translated by `@objectstack/platform-objects`
+and served from there, so they are **not** in your coverage number: an app that
+translated everything it declares reads 100%, not 39%. ⛔ Do not "fix" a low
+number by shipping your own `metadataForms` bundle — yours would override the
+platform's and go stale at the next upgrade.
+
+The rule is **ownership**, read from your own bundles rather than assumed: ship
+translations for that family and you are asked to complete them, which is how
+the platform packages stay gated on the strings they do own. Pass
+`--include-platform` to audit the baseline anyway (`os lint`'s flag, same
+meaning), or `--no-include-platform` to keep it out even though you ship part
+of it. The command prints how many keys it left out, and `--json` carries the
+same two numbers as `platformMetadataForms`.
+
 ### Which locales get checked
 
 Your project decides, and the tooling never assumes. `os lint`, `os i18n check`

skills/objectstack-i18n/SKILL.md

@@ -277,9 +277,10 @@ os i18n check --strict --threshold=95  # CI gate: locale parity + minimum covera
 
 It compares registered bundles against source metadata and reports missing keys
 per locale for every surface the extractor walks — objects and their sub-keys,
-global actions, apps, dashboards, pages, flow screens, metadata forms. Gaps in
-the default locale are errors, `--strict` promotes the rest, `--show-keys` lists
-them all; `os lint --i18n-strict` folds the same gate into lint.
+global actions, apps, dashboards, pages, flow screens. The platform's metadata
+forms count only for a stack that ships their translations (`--include-platform`
+audits them anyway). Gaps in the default locale are errors, `--strict` promotes
+the rest, `--show-keys` lists them all; `os lint --i18n-strict` folds it in.
 
 ### `os i18n extract --check` — freshness, not coverage