Electron app still crashing after nixos-rebuild: old process still running

After a NixOS rebuild that swaps an Electron app's build (e.g. removing a Discord mod like Vencord), the already-running instance keeps the old store path and keeps crashing until it is fully quit. Check the start time of the running process (ps -o lstart) against the rebuild time and its /nix/store path before debugging further. Separately, a bash rebuild script that calls nix eval on the system toplevel prints nothing for ~30s, so users read it as hung; echo a status line before it.