Buy Bitcoin short-changed the customer: a $5 buy at 1564 sats/USD with a
12% commission paid out 6056 sats instead of 6882 — an effective ~22.6%.
The commission was applied twice.
`calculateSats` already subtracts the fee (7820 gross → 6882 net) into
`context.satsAmount`. But `generateLnurlWithdraw` then passed that
already-net value as `principal_sats` to the server's create_withdraw,
which derives fee + net from the principal and subtracted 12% AGAIN:
[ATM Service] create_withdraw: principal=6882 fee=826 net=6056
This contradicted the function's own contract ("the ATM sends only the
hardware-attested gross principal; the operator side derives fee + NET").
The quote, the recorded transaction (sats=6882, fee_fraction=0.12), and
the on-screen commission (12%) all read a single fee — only the delivered
LNURL-withdraw amount was double-charged.
Fix: send the GROSS principal (fiat × rate, before commission), so the
server applies the fee exactly once. Now 7820 → server 12% → net 6882,
matching the quote/receipt. Exchange rate itself was always correct.
Verified: vue-tsc typechecks; math checks (gross=7820 fee=938 net=6882).
Hardware retest (one $5 buy → 6882) recommended before relying in prod.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
