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

Notes for agents

• The script (src/script.rs) is fixed text. Changing a step changes every host's transcript, which is the point; the crate's tests check the reference in-process service answers each step with the status the script says.
• A law that cannot be driven from outside (chat_a_copy_that_cannot_be_kept... needs a storage that refuses writes) is listed as N/A, never skipped silently.