Replit sandbox: what platform you're on

Field-verified platform facts only (2026-09-02/03, 2026-09-12, re-verified 2026-09-17, 2026-09-26). How to actually pull packages out of /nix/store (replit.nix, nix-env, closures) is the replit-nix skill. Hermes-on-Replit recovery (uv --locked trailing-slash failures, libatomic for PM-staged node): references/hermes-on-replit.md.

1. What survives a restart (the #1 gotcha)