A Spark destination amount does not disclose the exit's net economic recovery

What the evidence shows

Technical and product details

1. Fee mechanism

   Spark exit and refund transactions are pre-signed at zero fee; the user must fund their CPFP fee bumps from an independent on-chain UTXO. 1

   Supporting material shown on this page

   Blink fee-funding mechanicsPinned source code · github.com · checked 2026-07-14

   40## Step 2: fee funding from the same seed
   41
   42Exit transactions are pre-signed with zero fee and pay fees through CPFP
   43ephemeral anchors, so the exit needs an independent L1 UTXO to fund fee bumps.
   44The CLI derives a dedicated funding address from the wallet seed itself
   45(path `m/8797556'/<account>/0`, only the purpose hardened so a watch-only

2. Leaf triage

   Blink's recovery tool prices each leaf separately using the CPFP cost of its chain plus the final sweep cost, and skips leaves whose recovery cost exceeds their value by default. 2

   Supporting material shown on this page

   Blink leaf economicsPinned source code · github.com · checked 2026-07-14

   90Four leaves (32,768 + 32,768 + 16,384 + 8,192 sats) held 90% of the balance.
   91The other 18 — dust from routine wallet activity, some as small as 1 sat —
   92would each have cost 2,100–4,600 sats to exit: exiting everything would have
   93spent ~77.5k sats in fees to recover 100k. The tooling now computes this per
   94leaf and skips uneconomical leaves by default (`INCLUDE_UNECONOMICAL=1`
   95overrides; the economics math is regression-tested against this very bundle,
   96adapted to regtest, in

3. Accounting consequence

   Value swept to the destination, Spark value omitted as uneconomical, and separately supplied on-chain fee funding are different components. The destination amount alone therefore cannot establish the user's net economic recovery. 123

   Supporting material shown on this page

   Blink fee-funding mechanicsPinned source code · github.com · checked 2026-07-14

   40## Step 2: fee funding from the same seed
   41
   42Exit transactions are pre-signed with zero fee and pay fees through CPFP
   43ephemeral anchors, so the exit needs an independent L1 UTXO to fund fee bumps.
   44The CLI derives a dedicated funding address from the wallet seed itself
   45(path `m/8797556'/<account>/0`, only the purpose hardened so a watch-only

   Blink leaf economicsPinned source code · github.com · checked 2026-07-14

   90Four leaves (32,768 + 32,768 + 16,384 + 8,192 sats) held 90% of the balance.
   91The other 18 — dust from routine wallet activity, some as small as 1 sat —
   92would each have cost 2,100–4,600 sats to exit: exiting everything would have
   93spent ~77.5k sats in fees to recover 100k. The tooling now computes this per
   94leaf and skips uneconomical leaves by default (`INCLUDE_UNECONOMICAL=1`
   95overrides; the economics math is regression-tested against this very bundle,
   96adapted to regtest, in

   Blink exit accountingPinned source code · github.com · checked 2026-07-14

   111| **arrives at the destination address** | **89,668** |
   112| dust in 18 uneconomical leaves, left behind in Spark | 9,888 |
   113
   114Spark exit and refund transactions are pre-signed with **zero fee** (fees ride
   115the CPFP anchors), so each refund output carries the full leaf value; the only
   116deduction from the wallet balance itself is the final sweep fee.

4. Additional cost

   The transaction that funds the CPFP address is itself outside the displayed Spark balance and outside the destination amount. 13

   Supporting material shown on this page

   Blink fee-funding mechanicsPinned source code · github.com · checked 2026-07-14

   40## Step 2: fee funding from the same seed
   41
   42Exit transactions are pre-signed with zero fee and pay fees through CPFP
   43ephemeral anchors, so the exit needs an independent L1 UTXO to fund fee bumps.
   44The CLI derives a dedicated funding address from the wallet seed itself
   45(path `m/8797556'/<account>/0`, only the purpose hardened so a watch-only

   Blink exit accountingPinned source code · github.com · checked 2026-07-14

   111| **arrives at the destination address** | **89,668** |
   112| dust in 18 uneconomical leaves, left behind in Spark | 9,888 |
   113
   114Spark exit and refund transactions are pre-signed with **zero fee** (fees ride
   115the CPFP anchors), so each refund output carries the full leaf value; the only
   116deduction from the wallet balance itself is the final sweep fee.

Scope control

What this does not establish

• This does not establish that every Spark exit is uneconomical. The result depends on fee rate and each leaf's value and chain depth; large, shallow leaves can remain economical. 23

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.