Implements CNT-06, test-first. The finding names one file; there are two.

Why it works, and why that is the problem

A composable resolves its component through getCurrentInstance(), which is only set during setup. Called from inside a computed getter it works by accident: Vue's implementation is currentInstance || currentRenderingInstance, so while the getter runs as part of a render the rendering instance stands in.

That holds exactly as long as nothing evaluates the computed outside a render — a watcher, a pre-flush job, a unit test reading .value. vue-i18n throws MUST_BE_CALL_SETUP_TOP the moment it does.

ProseHeading.vue already has the right shape, with const { t, te } = useI18n() beside defineProps and the computed closing over it. Hoisting also stops the lookup repeating on every re-evaluation.

Verified on the page that renders them

Both components are blog-article prose, so I rendered an article with seven code blocks and an image:

7 × <pre … aria-label="Code in yaml">
<img … src="/images/blog/cluster-topology-social.png">

The interpolated "Code in yaml" is the proof that matters — it is the hoisted t producing a translated, parameterised string, not a fallback.

Then the whole article, before and after, ignoring <script> blocks: byte-identical, 99 961 both ways.

The guard

Flags any useX() call inside a computed(() => { … }) body across components, pages, layouts and composables. The self-test pins both directions — a call inside the getter is caught, the same call hoisted above it is not — so it cannot decay into matching everything or nothing.

Gates

Suite: 121 tests, 41 files. Build green. Ratchet unchanged at 334 / 39 / 21 (this branch is cut from d63bc02; #260 lowers the error count to 320 by a different route).

Refs: CNT-06

🤖 Generated with Claude Code

https://claude.ai/code/session_017uWFJwn6dswmNtR8kKB86s