For agents, on top of README.md, which they read first.

• A new crate with a build.rs needs a folder here when buckify warns that its fixup "does not say what to do". Read the build script, then write buildscript.run = true or false in <crate>/fixups.toml; most only probe rustc features and need true. Re-run buckify (../README.md).
• A build script that emits cargo:rustc-link-lib or rustc-link-search needs them kept explicitly (alsa-sys does), or the final link fails with undefined symbols.
• subsecond/fixups.toml's -Cdebug-assertions=yes is load-bearing. Removing it makes every hot patch a silent no-op (apps/hotdemo/CLAUDE.md has the measurement).
• Name a folder exactly as the crate: reindeer loads fixups/<name> only when a package of that name is in the graph. A folder left behind after a crate leaves the graph is never read and nothing reports it; delete it with the crate.
• Only README.md and CLAUDE.md may sit directly in this folder besides the crate folders; reindeer never looks a crate named either of those up, so they are inert.