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

• A new first-party buck package must be added to PACKAGES in BUCK, or it gets no manifest and :committed never looks for one. Buck cannot enumerate packages from inside a build, so that list is the one hand-kept input.
• The pgrx pin and panic = "unwind" profiles are written here, not copied by hand. Cancellation unwinds through the extension; a manifest that lost panic = "unwind" would abort the backend on Ctrl-C under cargo.
• The tools' invariants are one folder up, in tools/CLAUDE.md.