Slice 4 spec review caught: router.test.ts's narrow chrome.* shim
triggered 4 TS errors in webpack's ts-loader pass during production
builds (partial mocks don't match the full chrome.* type surface).
Plan's verbatim test body assumes tests aren't part of the build
compile. Add src/**/__tests__/** to tsconfig exclude — tests still
compile under Vitest's independent ts pipeline (42/42 passing).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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