Why: AGENTS.md is preloaded into every session via CLAUDE.md's @AGENTS.md
import, so every word is a tax paid whether or not it is relevant. It had
grown to 3,371 words (~4,550 tokens), 75% of it a single "Setup and testing"
section that was mostly neither: roughly 1,600 words were gate forensics —
why a hook is shaped the way it is, what was tried and rejected, verification
numbers — and only ~390 words were genuine one-time setup.
Implementation notes: split three ways by audience rather than by heading.
One-time setup, prerequisites and test commands move to a new root README.md,
which did not previously exist. The gate forensics move to a new
docs/spec/gates.md, preserving every constant, hook ID, error string and
tried-and-rejected note (policy.fetch_failure_default, the removed fallback
frontmatter reader, extending skill-size-check's files: pattern to agents,
tidying .claude/settings.json out of the pretty-format-json exclude list) —
these exist to stop settled decisions being re-litigated, so none were
dropped. AGENTS.md keeps only what applies every session, at one clause of
rationale per rule. The .apm/-mirror section collapses to a pointer because
docs/spec/architecture.md already covers it in full. The hot ADR-0020 gate
counts stay in AGENTS.md deliberately: they block any skill edit today.
Also corrects docs/spec/architecture.md's stale claim of 19 ADRs; ADR-0020
landed without updating the count.
Impact: per-session preload drops from ~4,550 to ~1,116 tokens, a 75% cut.
agentsmd-audit passes: secrets clean, drift clean, 4 informational findings
for sections deliberately relocated to the README.
