diff --git a/docs/nostr-patterns/replaceable-events.md b/docs/nostr-patterns/replaceable-events.md
index 0cad379..f02158b 100644
--- a/docs/nostr-patterns/replaceable-events.md
+++ b/docs/nostr-patterns/replaceable-events.md
@@ -7,15 +7,19 @@ in this file follows from that single fact.
 
 ## Strictly-monotonic `created_at` per coord
 
-**Canonical:** `src/modules/events/composables/useRSVP.ts` —
-`lastPublishAt` map + the `Math.max(now, previous + 1)` line.
+**Canonical helper:** `src/lib/nostr/timestamp.ts` —
+`monotonicCreatedAt(lastCreatedAt, now?)` returns `max(now, last + 1)`.
+Use it for **every** replaceable-event publish; track the last
+`created_at` per coord (a `Map<coord, number>` when one composable
+publishes many coords like `useRSVP.ts`, or a single field when there's
+one coord per user like `useBookmarks.ts`' kind-10003 list).
 
 ```ts
+import { monotonicCreatedAt } from '@/lib/nostr/timestamp'
+
 const lastPublishAt = new Map<string, number>()
 
-const now = Math.floor(Date.now() / 1000)
-const previous = lastPublishAt.get(coord) ?? 0
-const createdAt = Math.max(now, previous + 1)
+const createdAt = monotonicCreatedAt(lastPublishAt.get(coord))
 …
 lastPublishAt.set(coord, signedEvent.created_at) // only after publish success
 ```