diff --git a/PROTOCOL.md b/PROTOCOL.md
index 7ecaa9c..2886d84 100644
--- a/PROTOCOL.md
+++ b/PROTOCOL.md
@@ -59,6 +59,12 @@ A certificate moved that way must be anchored by an `UPD` before it can be relea
 
 ## Resolver rules (indexer-enforced)
 
+**One message per transaction.** A transaction's message is the one output
+that parses as a BNS payload with a known operation. If more than one output
+does, the transaction carries **no** message. *(2026-10-04. Before, the last
+one won — which let whoever assembles a transaction replace a message another
+party had fixed in it. No transaction on chipnet carried more than one.)*
+
 1. Fetch beacon history, sort by `(height, txid)`; unconfirmed last.
 2. **Then reorder causally:** never index a transaction before one it spends
    from. Independent transactions keep the `txid` tiebreak. *(See "Ordering"