split machine-specific stores into mask hooks

user/CLAUDE.md

@@ -89,11 +89,16 @@ chat histories, and that is the copy that matters to him.
 
     printf '%s' '<secret>' | ~/projects/claude-mds/tools/mask-secret.py
 
-The script covers both readable stores — Claude Code's `~/.claude/projects/**`
-transcripts and Postgres `chat_session_events` — and replaces the value with
-asterisks of the same length, overwriting in place so the live session's
-appends are not lost. Read the header before changing it; the same-length,
-same-inode detail is load-bearing.
+It masks Claude Code's own transcripts (`~/.claude/projects/**/*.jsonl`) with
+asterisks of the same length, overwriting in place so the live session's appends
+are not lost. Read the header before changing it; the same-length, same-inode
+detail is load-bearing.
+
+That is all this rule owns. **A machine that keeps its own second copy of the
+chat — a database, a mirror, a log shipper — declares it as a hook** in
+`tools/mask-hooks.d/`, and the script runs whatever it finds there. Do not add
+machine-specific stores to this file; add a hook, and describe it in that
+project's own `CLAUDE.md`.
 
 **Do not mask a throwaway.** He sometimes sets a real password aside, hands you
 a temporary one so you can drive an API — Nginx Proxy Manager, a router, a