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>