draw_save_ui held both an EventReader<RequestSaveOpen> (to know when the View
menu opened it) and an EventWriter<RequestSaveOpen> (so its own "Open savedata…"
button could re-trigger the file dialog). Bevy rejects a system that accesses
one event type both ways, and does so at schedule-validation time -- so the app
panicked on startup, before any window content.
The button now sets `SaveBrowser::request_open` and handle_save_open_request
treats that flag as equivalent to the event, with no path (dialog).
Audited every system in the viewer for the same shape; this was the only one.
Verified by running the binary to steady state rather than by compiling alone,
since a param conflict is invisible to the type checker.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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