test(desktop): pin the composer mention catalog's context guard #4892

composer-mentions.tsx:132 derives what the composer shows while a Skill catalog is reloading:

const liveCatalog = catalog.contextKey === contextKey
  ? catalog
  : { contextKey, loading: true, settled: undefined, skills: EMPTY_SKILLS };

The cached catalog is keyed on contextKey — session id, model, collaboration mode, permission mode, new-task target — and when the context has moved on, the provider must publish a loading placeholder rather than the previous context's Skills. Otherwise a session switch briefly offers the Skills of the session you just left, and mentionSkillsUnavailable reports the old verdict.

Nothing currently fails if that ternary is inverted. The only coverage near it is a Storybook story (ContextSwitchStartsWithALoadingCatalog), which drives the whole composer through a real browser to observe an aria-busy attribute — it does not pin this derivation, and it is the more expensive of the two places this could live.

What to do

Write a unit test for it in the seam this file already sits in. No new tooling is needed:

• tsconfig.main.json compiles whatever the main graph imports, so renderer modules reachable from a test are emitted to apps/desktop/dist/renderer/. composer-mentions.js is already there.
• apps/desktop/src/main/__tests__/ holds ~146 tests that import renderer modules this way, and 18 of them render React components with linkedom + createRoot under node --test. agent-graph-panel.test.ts and composer-model-picker-recovery.test.tsx (in packages/ui) are both good models.

Suggested shape: mount ComposerMentionsProvider with a sessionId, let its catalog settle, switch sessionId, and assert that the value published through useComposerMentionsContext reports mentionSkillsLoading: true and empty mentionSkills before the new load resolves — while a same-context refresh keeps the Skills already on screen (that second half is the #2667 regression the surrounding comment describes, and it is worth pinning in the same test file).

Acceptance

Invert the ternary at composer-mentions.tsx:132 and the new test must fail. Restore it and it must pass. Run it with:

npm --workspace @maka/desktop run build:main
cd apps/desktop && node --test --test-concurrency=4 "dist/main/__tests__/<name>.test.js"

Notes

Do not add a test runner. Vitest, jsdom, and a second tsc target were all considered and are unnecessary — this file is already reachable from node --test today.

The directory name is misleading: renderer unit tests live under src/main/__tests__ because that is the tsc project that emits them. Relocating them is a separate change with its own constraints (check-stale-dist maps src/renderer to dist-renderer, and check:architecture enumerates the renderer tree), so please do not do it here.