diff --git a/CLAUDE.md b/CLAUDE.md
index d6ce8df..b9364af 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -68,3 +68,8 @@ you change observable behaviour, update the doc in `docs/` that describes it in
 Ask in the PR rather than guessing at the interface. A day of clarification is cheaper than
 an M2 integration rewrite. And record real decisions as an ADR in `docs/adr/` — the next
 agent to touch this will have none of your context.
+
+**ADR numbers:** there is no allocator. Take the next free number in `main`'s
+`docs/adr/` (gaps from reserved-but-unwritten entries are fine to fill). Lanes draft in
+parallel, so collisions happen: whoever merges **second** renumbers, updates any
+cross-references, and keeps going — it is not worth a round trip.