C4, first wave. Twenty places each stored the same fact — how to translate when
the host never installed vue-i18n — and two of them, usePplrT.js and
useNeighborT.js, were whole-file near-duplicates at Jaccard 0.82. That pair was
the curation audit's evidence that the guard was being COPIED rather than shared.
Both now call library/composables/useOptionalT.js and keep their public names, so
no call site changes.
★ THE SPEC ASKED FOR (namespace, fallbackCatalogue) AND THE CATALOGUE IS
UNNECESSARY. Every copy imported its own English JSON and hand-walked it after
stripping the namespace prefix. But library/i18n builds `messages[locale][area]`
keyed by the JSON's own filename, and tStatic() already walks that tree and
already falls back to English. So `import enPplr from '.../en/pplr.json'` was a
second copy of bytes the bundle already had, and the helper takes one argument.
★ AND IT IS NOT A SIZE REGRESSION, which was the one good reason the narrow
import might have existed. The build NARROWS library/i18n's catalogue glob per
bundle to the areas internal/i18n-areas.mjs finds in that bundle's source graph
(check:i18n-treeshake). A bundle that says 'pplr.' gets the pplr area, not the
other thirty. Verified before writing the helper, because "the obvious dedup
makes every bundle carry every locale" would have killed it.
Resolution order, each step earning its place: the host's own vue-i18n when it
installed one, so a host managing locale keeps control; then tStatic, which
honours the runtime locale and falls back to English; then the key itself, so a
missing string is visible rather than blank. The middle step also covers i18n
being present but empty — i18n.t() returns the key unchanged, which every copy
of this pattern already treated as "not found".
Verified by _qa-cycle/02-builder-cycle/_chk-c4-optional-t-equivalence.mjs: 18
assertions across all three host states, with a branch-for-branch equivalence
check against the old hand-written implementation and two negative controls. It
extracts and executes the module source, because useOptionalT imports vue-i18n
and an i18n index that calls import.meta.glob, which plain Node cannot run.
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