ver 0.9

echo-memory.plugin.src/skills/echo-memory/references/vault-layout.md

@@ -46,9 +46,13 @@
     ├── health/        ← YYYY-MM-vault-health.md (monthly self-maintenance audit; NOT a journal entry)
     ├── templates/     ← canonical note templates
     ├── skills/        ← active / archived
-    └── heartbeat/     ← single-line pointers (e.g. last-session.md → most-recent session log path)
+    ├── heartbeat/     ← single-line pointers (e.g. last-session.md → most-recent session log path)
+    ├── index/         ← entities.json — machine-maintained slug→{path,kind,title,aliases} registry
+    └── locks/         ← vault.lock — cooperative advisory multi-writer lock
 ```
 
+**Entity index:** `_agent/index/entities.json` is a machine-maintained registry mapping each entity slug to its `{path, kind, title, aliases, last_seen}`. It makes routing/resolve an O(1), alias-aware lookup (no fuzzy search per write) and supplies the name→path map for cross-linking and recall. It is rebuilt automatically by `echo.py capture` and by `sweep.py`; do not hand-edit. The only JSON file in the vault.
+
 **Heartbeat:** `_agent/heartbeat/last-session.md` is a one-line pointer (`<session-log-path> @ <ISO-timestamp>`) the **session-logging procedure writes (PUT, overwrite) at session end** and the **loading procedure reads first (Step 4)** as an O(1) shortcut to the latest session log. It is a hint, not a source of truth — fall back to the `sessions/` directory listing if it's missing or stale. Because it's PUT-overwritten, it never grows or duplicates.
 
 **Slug rules:** kebab-case, ASCII only, truncate to ~40 chars.