The header rendered both a "Missions" desktop span AND a mobile span
containing the selected mission title simultaneously, relying on CSS to
hide the inactive variant. jsdom doesn't apply media queries, so
testing-library's getByText found the mission title in both the body
cards and the otherwise-hidden mobile header — failing 49 tests with
"Found multiple elements with the text: <title>". Render only the
active variant based on isMobile.
Also clear localStorage in beforeEach so the SWR mission cache from
prior tests doesn't pre-hydrate into the next render and surface its
own fixtures as duplicates.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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