Merge pull request 'fix(ecash): change proofs no longer ride along inside sent tokens — double-credit bug' (#122) from fix/cashu-double-credit into main

core/archipelago/src/wallet/ecash.rs

@@ -632,11 +632,30 @@ pub async fn send_token_at(data_dir: &Path, mint_url: &str, amount_sats: u64) ->
         // Mark original proofs as spent
         wallet.mark_spent(&indices);
 
-        // Separate send proofs from change proofs
+        // Separate send proofs from change proofs BY COUNT, not membership:
-        let (send, change): (Vec<_>, Vec<_>) = swap_result
+        // partition(contains) put EVERY proof whose denomination appeared in
-            .new_proofs
+        // send_denoms into the token — when change shared a denomination with
-            .into_iter()
+        // the send (worst case: spending from a proof worth exactly 2× the
-            .partition(|p| send_denoms.contains(&p.amount));
+        // amount, send [n] + change [n]), the change proofs rode along and the
+        // receiver was credited double. Consume exactly one proof per needed
+        // send denomination; everything else is change.
+        let mut send_needed = send_denoms.clone();
+        let mut send: Vec<Proof> = Vec::new();
+        let mut change: Vec<Proof> = Vec::new();
+        for p in swap_result.new_proofs {
+            if let Some(pos) = send_needed.iter().position(|&d| d == p.amount) {
+                send_needed.swap_remove(pos);
+                send.push(p);
+            } else {
+                change.push(p);
+            }
+        }
+        if !send_needed.is_empty() {
+            anyhow::bail!(
+                "Mint swap returned incomplete send denominations (missing {:?})",
+                send_needed
+            );
+        }
 
         // Add change proofs back to wallet
         if !change.is_empty() {