docs: REUSE.md introduced — cross-repo reuse map (exec/format-safety guards, durable-id seams, traps; docs-only, no version bump)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

CHANGELOG.md

@@ -1,3 +1,13 @@
+## docs — REUSE.md introduced (2026-07-03)
+
+Cross-repo reuse-map rollout (docs-only, no code change, no version bump). New `REUSE.md` at the
+repo root: curated map of canonical helpers (48 rows — exec/sudoers surface, format-safety guards,
+durable-id seams, stores, local-API plumbing), patterns, dangerous lookalikes (req.Device TOCTOU,
+raw mkfs, uuid:-vs-byid: scheme confusion, MemoryNonceStore, pool-blind stale-lock scan…), test
+seams, extension points, and observed duplication (7 clusters, NOT fixed). Every entry code-verified
+at file+symbol; cited paths machine-checked by `felhom.eu/scripts/reuse_refs_check.py` (green).
+CLAUDE.md gains the "See REUSE.md before writing new code" pointer + the same-commit maintenance rule.
+
 ## v0.61.0 — blast-radius audit fixes B1 + D1 + D2 + D3 (2026-07-03)
 
 Four LOW/INFO fixes from `AUDIT-blast-radius-hostroot-localapi-2026-07-02.md` — the "second gate must