docs(i18n): consumer sweeps, destructuring defaults, and unowned shared copy (#2204)

Co-authored-by: Kandev Agent <agent@kandev.dev>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/i18n.md

@@ -296,6 +296,23 @@ trusting the count. Install/update flows and any maintenance action are the
 toast-heavy cases. A count from `pnpm run lint:i18n` is a floor on the visible
 half, never a work-list.
 
+**Default values in a destructuring pattern are a third invisible shape, and the
+fix is not the obvious one.** `ActionButtonContent` carried three:
+
+```tsx
+export function ActionButtonContent({
+  pendingLabel = "Running...",   // NOT flagged — not a literal in JSX
+  successLabel = "Done",
+  errorLabel = "Failed",
+}: Props) {
+```
+
+These are evaluated in the parameter list, which runs *before* the component
+body, so a `const { t } = useTranslation()` in the body is not in scope for them —
+you cannot fix this in place. Resolve the fallback inside the body instead
+(`const pending = pendingLabel ?? t("system:jobRunning")`). Prop defaults on a
+shared presentational component are a common home for this.
+
 `externalize-strings.mjs`
 covers those shapes — it walks `.ts` as well as `.tsx` and handles template
 literals and dialog/toast arguments — but **a zero from `pnpm lint` does not by
@@ -490,6 +507,50 @@ While the migration is in flight, an unmigrated screen is expected to be full of
 plain English — pseudo only proves anything about screens whose components are on
 the `i18nGuardFiles` allowlist.
 
+### Walk it by consumer, not by route
+
+Which screens you walk matters as much as what you look for. A component's copy
+is verified by walking **every route that mounts it** — not the routes your
+migration owns.
+
+The natural method fails here. Walking the import closure *from your own pages*
+traverses the graph in the wrong direction: it finds what your routes render, and
+by construction never finds a route that renders *you*. One migration hit it in
+both directions — the cards it converted mount only on a sibling migration's
+route, and a card that sibling owned mounts on its own. Neither could have been
+verified from its own pages alone.
+
+`job-progress-indicator.tsx` is the worked example. It reported **0** findings,
+because its `Queued` / `Running` / `Done` / `Failed` come out of a plain `switch`
+in a non-JSX function, and it has four consumers spanning two directories
+(`database-stats-card`, `disk-usage-card`, `backups-table`, and Storage's
+`storage-quarantine-card`). Three separate migrations rendered it, and each left
+it — a component every one of them touched, and none of them owned. The System
+migration finally took it and walked Storage's already-merged route to confirm.
+
+Per component you touch:
+
+```bash
+grep -rn '<JobProgressIndicator' apps/web/app apps/web/components
+```
+
+then walk each of those routes under pseudo, whoever owns them. If a consumer
+belongs to an unmigrated directory, note it in the guard comment rather than
+silently leaving it — the next migration inherits the answer instead of
+rediscovering the question.
+
+### Copy that belongs to no directory
+
+A file shared by *every* area has no natural owner and so gets skipped by all of
+them. `src/settings-routes.tsx` holds the live title and description for every
+settings route in one `SETTINGS_ROUTES` map — a SCREAMING_CASE identifier the
+guard skips entirely, in a 650-line file no single migration's closure claims.
+
+The rule: a migration converts the entries it owns but must **not** add such a
+file to `i18nGuardFiles`, because allowlisting it claims a completeness nobody
+has. The last area to migrate adds it. Say so in your guard comment, naming which
+entries are still English and who owns them.
+
 ## Adding a real language
 
 1. Add the locale to `SUPPORTED_LOCALES` + `LOCALE_LABELS` in