#36071 refactor: fuzz: remove cost_of_change from coin-grinder fuzz target

• Clean up dead setup code in wallet coin-grinder fuzz tests
• Avoid setting an unused parameter that has no effect on the algorithm

Removes an unused assignment to `coin_params.m_cost_of_change` from the `coin_grinder` fuzz harness in `src/wallet/test/fuzz/coinselection.cpp`. The coin-grinder selection algorithm does not use that parameter.

Problem: The fuzz test harness sets a variable that is ignored by the coin-grinder algorithm, leaving dead setup code in the test.

P4 · cleanup

• P4 because it is a minor cleanup in test code
• Has no functional impact on wallet logic or fuzzing efficacy

P4 as a minor cleanup in test code. As brunoerg noted, the assignment is a no-op in this target, so removing it has no functional impact on wallet logic or fuzzing efficacy.

Membership: Modifies the wallet coin selection fuzz harness in `src/wallet/test/fuzz/coinselection.cpp`.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 0

• Ready for review now
• Single-line test cleanup with no conflicts or failing checks

The change is a single-line test cleanup with no conflicts or failing checks.

Author status: silent since submission on 2026-08-24

• Approved confirming the assignment is dead code and a no-op in the target (brunoerg)

Approved with rationale confirming the assignment is dead code (brunoerg)

brunoerg confirmed that `m_cost_of_change` is unused by coin-grinder and approved the removal.

• brunoerg ACKed: 'm_cost_of_change isn't used for anything of coin-grinder, it's a no-op in the target and it's fine to remove it.'

Review verdicts (DrahtBot): 1

• ACK: brunoerg

1 lines under test/bench/ci.

• src/wallet/test/fuzz/coinselection.cpp +0/-1

PR 36071 removes an unused assignment of `m_cost_of_change` from the `coin_grinder` fuzz target in wallet tests. The coin-grinder algorithm does not consume that parameter, making the setup dead code. This is a minor test cleanup with no user-facing impact or change to fuzzing coverage. Review is ready and approved by one reviewer with no objections.