fix(hooks): keep hooks.json within Claude Code's schema

Move stable hook metadata to a validated sidecar while preserving hook commands and installer identity. Reject moved fingerprints and duplicate IDs, and validate before updating metadata. Independent local review passed at c315271624a1fd055b992f2bff889ad2a0ff8a6b; CI run 34678210149 passed. Rollback: revert this squash commit.

hooks/README.md

@@ -19,6 +19,10 @@ User request → Claude picks a tool → PreToolUse hook runs → Tool executes
 Memory persistence lifecycle definitions live in `hooks/memory-persistence/`.
 The executable hook graph remains `hooks/hooks.json`; the memory persistence directory is the stable contract for SessionStart, PreCompact, observation, activity tracking, and SessionEnd behavior.
 
+Stable hook IDs and descriptions live in `hooks/hooks.metadata.json`, aligned by event and index with `hooks/hooks.json`. Claude Code validates a plugin's `hooks.json` against its own schema and reports any other key (`$schema`, `id`, `description`) as unknown at load time, so `hooks.json` carries only what the harness accepts. ECC's installer, validator, and dashboard merge the sidecar back in through `scripts/lib/hooks-config.js`; `node scripts/ci/validate-hooks.js` fails if the two files drift apart.
+
+Each sidecar entry also carries a `fingerprint` of the matcher entry it describes (matcher plus hook commands), so reordering `hooks.json` without reordering the sidecar, or editing a command without updating the sidecar, is caught rather than silently swapping IDs. When reordering hooks, move the matching sidecar entries first. Then run `node scripts/ci/validate-hooks.js --update-fingerprints` to refresh changed commands and commit both files. The updater rejects known fingerprints at different positions and writes only after validation succeeds.
+
 ## Installing These Hooks Manually
 
 For Claude Code manual installs, do not paste the raw repo `hooks.json` into `~/.claude/settings.json` or copy it directly into `~/.claude/hooks/hooks.json`. The checked-in file is plugin/repo-oriented and is meant to be installed through the ECC installer or loaded as a plugin.