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

Notes for agents

• The policy is decide and nothing else. Change thresholds and topic handling there, with a test.
• Topic order is part of the question. Jev has a measured order bias; re-measure before reordering Topic::ALL.
• No I/O, and it must build for wasm (the website links it). Do not add a client, a file or a clock here.
• The website's tests (web/site/src/jev.rs) hold its pages to this crate; a change here that the page does not follow fails them.