f - Limit is_outpoint_spent lookback to avoid fuzz hash collisions

Author: jkczyz

fuzz/src/chanmon_consistency.rs

@@ -207,7 +207,11 @@ impl ChainState {
 	}
 
 	fn is_outpoint_spent(&self, outpoint: &bitcoin::OutPoint) -> bool {
-		self.blocks.iter().any(|(_, txs)| {
+		// Only check the last 6 blocks (1 confirmation block + 5 post-confirmation) to avoid
+		// false positives from hash collisions in older blocks. Under fuzz hashing, txids have
+		// only 8 effective bits, so unrelated outpoints in old blocks frequently collide.
+		let start = self.blocks.len().saturating_sub(6);
+		self.blocks[start..].iter().any(|(_, txs)| {
 			txs.iter().any(|tx| {
 				tx.input.iter().any(|input| input.previous_output == *outpoint)
 			})