The reviewed CPFP recovery route needs external on-chain fee funding

What the evidence shows

Technical and product details

1. Documented mechanism

   In the current procedure, pre-signed Spark exit and refund transactions pay zero fee and are relayed with fee-paying CPFP children. 12

   Supporting material shown on this page

   Spark unilateral-exit manualOfficial documentation · docs.spark.money · checked 2026-07-14

   Spark package constructorPinned source code · github.com · checked 2026-07-14

   1// unilateral-exit.ts

2. Manual requirement

   Spark tells mainnet users to bring sufficient L1 UTXOs and use Bitcoin Core v29 submitpackage. 1

   Supporting material shown on this page

   Spark unilateral-exit manualOfficial documentation · docs.spark.money · checked 2026-07-14
3. Timing consequence

   The Spark value is not yet available as an ordinary spendable L1 output when those fee children must be funded. 12

   Supporting material shown on this page

   Spark unilateral-exit manualOfficial documentation · docs.spark.money · checked 2026-07-14

   Spark package constructorPinned source code · github.com · checked 2026-07-14

   1// unilateral-exit.ts

4. Independent-user consequence

   A user relying only on the documented independent path cannot begin with a Spark balance alone; an external fee source must first supply a suitable UTXO. 13

   Supporting material shown on this page

   Spark unilateral-exit manualOfficial documentation · docs.spark.money · checked 2026-07-14

   Blink funding transactionWeb source · blockstream.info · checked 2026-07-14

Scope control

What this does not establish

• The external UTXO need not always be personally supplied by the user. A wallet or sponsor could provide fee funding, but that replaces the user-funding requirement with dependency on that sponsor. It does not remove the documented standard-relay path's requirement for a fee-paying input outside the Spark balance. The external-fee-input requirement is specific to this CPFP route. Already-presigned direct/refund variants may work under their own ancestry, maturity and fee conditions; they are not a guaranteed alternative for every leaf. 4

Sources and excerpts

Primary sources

The relevant details and available source-code excerpts appear alongside the claims above. This list preserves the complete original-source trail for independent verification.