useDashboardHealth fetched /api/health once on mount and never again. Right after a project is
created the engine is still starting, so that single fetch reports engine.available=false and the
"AI engine is not running" banner shows — and because health was never refreshed, the banner stayed
up even after the engine came online (the user reported the banner while the engine was in fact
running). Poll every 15s and preserve the last value on transient errors so the banner clears on its
own once the engine reports available.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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