Owner-validated sell RPC refunds SellRefundPercent of invested gold (Wall refunds 100% while un-upgraded), despawns the tower, and broadcasts a coin-burst VFX + rustle SFX. Refunds do not count as per-wave income. Investment/upgrade tracking added as the seam for the future upgrade system.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>