The tool surface is self-describing — most of what's below, an agent discovers on its own. These pages exist for the human reviewing its work.
Every error is {error, code} from an append-only registry. Validation failures carry ConstraintIssue[] with field, constraint, limit and a fix hint.
Strong ETags on every delivery read, 304 on revalidate. Image derivatives serve 1-yr-immutable redirects.
Composition rules: hooks gate synchronously, events run async, computed fields derive, CAS writes back. test_hook dry-runs without writing.