The recovered bottom apron had been represented as one solid collision segment,
which prevented the ball from reaching the drain threshold. Split that apron
around the visible center drain so a lost ball decrements the ball count and
allows player and game-over progression to continue.
Add a conservative ball-search impulse after three seconds below the movement
threshold. This protects long-running games from other low-energy rests without
changing active trajectories, and reuses the original nudge sound as feedback.
Test Plan:
- `cargo fmt -- --check` -- passed
- `cargo test --all-targets` -- passed, including drain and ball-search regressions
- `cargo clippy --all-targets -- -D warnings` -- passed
- `git diff --check` -- passed
ddidderr
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