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fix(ecash): change proofs no longer ride along inside sent tokens — double-credit bug

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send_token_at split the mint swap's results with
partition(send_denoms.contains(amount)) — membership, not count. When a
change denomination equaled a send denomination (guaranteed when
spending from a proof worth exactly 2x the amount: send [n], change
[n]), the change proofs were serialized INTO the token, and the
receiver redeemed double. Both the wallet send flow and peer-files
purchases mint through this path.

The split now consumes exactly one proof per required send denomination
(everything else returns to the wallet as change) and hard-fails if the
mint returns an incomplete denomination set, so a token can never again
be silently over- or under-packed.

Note: tokens minted BEFORE this fix already contain the extra proofs
and will still redeem at their inflated value.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Dorian 2026-07-24 13:34:48 +01:00
parent df88d6d00a
commit 98e15b3af0
1 changed files with 24 additions and 5 deletions
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29
core/archipelago/src/wallet/ecash.rs
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@ -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
let (send, change): (Vec<_>, Vec<_>) = swap_result
.new_proofs
.into_iter()
.partition(|p| send_denoms.contains(&p.amount));
// Separate send proofs from change proofs BY COUNT, not membership:
// partition(contains) put EVERY proof whose denomination appeared in
// send_denoms into the token — when change shared a denomination with
// the send (worst case: spending from a proof worth exactly 2× the
// 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() {