Wallet usage history—not just balance—determines Spark's exit workload

What the evidence shows

Technical and product details

1. Fragmentation mechanism

   Blink explains that ordinary payments split and re-split the Spark tree, causing a wallet to accumulate multiple leaves. 1

   Supporting material shown on this page

   Blink wallet-tree mechanicsPinned source code · github.com · checked 2026-07-14

   12A mobile Spark wallet holding **100,000 sats spread across 22 leaves**. Spark
   13wallets accumulate leaves through normal use (payments split and re-split the
   14tree), and each leaf carries its own exit chain: the on-chain transactions
   15that must confirm, level by level, to force the leaf onto Bitcoin without
   16operator cooperation. For this wallet that meant **253 transaction packages**
   17across the 22 chains — for 100k sats.

2. Per-leaf graph

   Every current leaf carries its own chain of ancestor and refund transactions that must be forced onto Bitcoin. 1

   Supporting material shown on this page

   Blink wallet-tree mechanicsPinned source code · github.com · checked 2026-07-14

   12A mobile Spark wallet holding **100,000 sats spread across 22 leaves**. Spark
   13wallets accumulate leaves through normal use (payments split and re-split the
   14tree), and each leaf carries its own exit chain: the on-chain transactions
   15that must confirm, level by level, to force the leaf onto Bitcoin without
   16operator cooperation. For this wallet that meant **253 transaction packages**
   17across the 22 chains — for 100k sats.

3. Sequential depth

   Mempool policy requires each level within a leaf's chain to confirm before the next level can enter the mempool. 2

   Supporting material shown on this page

   Blink TRUC sequencingPinned source code · github.com · checked 2026-07-14

   72one unconfirmed parent plus one child — that is what makes the pre-signed
   73zero-fee exit transactions safely fee-bumpable, and it also means **each level
   74of an exit chain must confirm before the next level can enter the mempool**.
   75A 15-package chain takes at least 15 blocks, no matter how it is submitted.
   76Any tooling that fires packages back-to-back will strand everything after the
   77first package per chain.

4. Mechanical consequence

   Exit work is governed by the number of leaves and the depth of their chains, information that a displayed aggregate balance does not convey. 12

   Supporting material shown on this page

   Blink wallet-tree mechanicsPinned source code · github.com · checked 2026-07-14

   12A mobile Spark wallet holding **100,000 sats spread across 22 leaves**. Spark
   13wallets accumulate leaves through normal use (payments split and re-split the
   14tree), and each leaf carries its own exit chain: the on-chain transactions
   15that must confirm, level by level, to force the leaf onto Bitcoin without
   16operator cooperation. For this wallet that meant **253 transaction packages**
   17across the 22 chains — for 100k sats.

   Blink TRUC sequencingPinned source code · github.com · checked 2026-07-14

   72one unconfirmed parent plus one child — that is what makes the pre-signed
   73zero-fee exit transactions safely fee-bumpable, and it also means **each level
   74of an exit chain must confirm before the next level can enter the mempool**.
   75A 15-package chain takes at least 15 blocks, no matter how it is submitted.
   76Any tooling that fires packages back-to-back will strand everything after the
   77first package per chain.

5. Mitigation

   Blink recommends consolidating leaves while Operators are cooperative, confirming that prior wallet activity affects the later emergency-exit burden. 3

   Supporting material shown on this page

   Blink consolidation takeawayPinned source code · github.com · checked 2026-07-14

   1991. **A unilateral exit is a fire escape, not a door.** 253 packages, one
   200   block per package per chain, two weeks of timelock, and fees that would
   201   have consumed 79% of the balance if applied indiscriminately — for a
   202   100k-sat wallet. With economic triage, ~90% of the balance reached the
   203   destination. Self-custody on Spark is real, but the exit path is expensive
   204   and slow by construction; size expectations accordingly.

Scope control

What this does not establish

• Leaf count and chain depth vary by wallet, and consolidation can reduce future work. This establishes history-dependent workload, not a fixed transaction multiplier or technical impossibility. 123

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.