Canonical instructions live in PROTO.md. Read it before editing — it
owns the stack, the lint+test gate, the per-agent gating design (§4, don't break
it), the tool inventory + error classification (§5), the rules (§6, incl. host-free
imports, plain-string @tool docstrings, and never-raise tools), and the release
recipe (§7). This file is a thin pointer; edit PROTO.md.