OnboardingPlugin previously used PostStartup which fires before the
first Update tick — guaranteeing the onboarding modal and the launch
splash (MOTION_SPLASH_TOTAL_SECS = 1.6 s) overlap for the entire
splash duration. The splash sits at Z_SPLASH (the highest UI z-index),
so the two screens fought visually and the user saw a confusing frozen
composite before the splash faded out.
Fix: move spawn_if_first_run to Update and gate it on
`splashes.is_empty()` (no SplashRoot entity alive). A Local<bool>
ensures the spawn fires at most once per session. Cost: ~one frame of
latency after the splash clears, which is imperceptible.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
funman300
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