invoices: sell merchant-supplied preimages via a usePreimage queue

Merchants POST /preimages (auth) to pre-load 32-byte hex preimages into a
FIFO queue; creating an invoice with usePreimage: true consumes the next
one so the invoice's payment hash is sha256(preimage). Paying the invoice
reveals the merchant-chosen secret to the buyer — via their own wallet on
external settlements, and via GET /invoice/:id once settled — enabling
backend-less digital download stores (encrypted files on static hosting,
preimage + public string = decryption key).

- GET /preimages lists the queue with payment hashes so the merchant can
  map files to future invoices; POST /preimages/delete clears it
- empty queue fails invoice creation rather than issuing a random
  preimage the buyer would pay for but couldn't decrypt with
- preimages cln rejects as already used are discarded and the next tried
- consumed preimages persist at preimage:${payment_hash} (TTL = invoice
  expiry) and credit() prefers them as the settlement ref, so internal
  coinos-to-coinos payments reveal the real preimage instead of the
  sender's uid

Co-Authored-By: Claude Fable 5 <[email protected]>

0 files changed, 0 insertions, 0 deletions