1@README.md
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3- **Tool paths come from `.buckconfig.local` `[nix]`, which the devshell
4  writes.** Use `read_root_config` here: a cell's own `read_config` doesn't
5  see the root's local config.
6- **`-Copt-level` must stay explicit:** the prelude derives build scripts'
7  OPT_LEVEL from it, and cc-rs fails without that.
8- **`rust.rustc_identity` must stay a hard failure when unset.** A fallback
9  placeholder would put every compiler under one cache key again and bring
10  back E0514 from the shared cache (hit 2026-09-30).