fix(wallet): include fees when selecting inactive proofs

[mmalmi]

Description

When inactive-keyset proofs cover the requested amount before fees, selection returns early without honoring include_fees. An 8-sat proof at 500 ppk leaves only 7 sats after redemption. Apply the existing fee-coverage helper while retaining keyset and coin-age preferences.

Notes to the reviewers

Four regressions fail before the fix; all 51 proof-selection tests pass afterward, including fee opt-out and age ordering. Targeted Clippy, formatting and whitespace checks pass. Independent of #2499; no public API or database changes.

Full just quick-check passes on the current PR head (88469ae6) with Rust 1.98.0, nixpkgs-fmt 1.3.0 and typos 1.46.3. Changed Rust files also pass the repository’s nightly rustfmt import rules.

Suggested CHANGELOG Updates

FIXED

• Include redemption fees when selecting inactive-keyset proofs.

Checklist

• Followed the code style guidelines.
• Ran just quick-check on the current PR head.
• Wallet API unchanged; no FFI update needed.

[j-kon]

Findings

• No critical, warning, or nit-level issues found.
  • Corrects an early return in select_proofs where inactive proofs bypassed include_fees: true, leading to insufficient fund calculations when keysets were rotated.
  • Appropriately routes selected inactive proofs through Self::include_fees.
  • Added comprehensive test coverage in inactive_fee_tests.rs verifying fee coverage, shortfall handling with active proofs, and derivation index age preference.

Summary

Reviewed proof selection logic in crates/cdk/src/wallet/proofs.rs and the new test suite in crates/cdk/src/wallet/proofs/inactive_fee_tests.rs. The fix correctly ensures fee requirements are fulfilled when spending inactive keyset proofs.

Verdict

APPROVE

[thesimplekid]

@cdk-bot review

[cdk-bot]

Verified findings approved for disclosure:

• Fee top-up on inactive-proofs branch never reconsiders equal-nominal lower-fee subsets, causing avoidable over-selection (low) - see inline comment
  Unanchored locations included in summary:
  • crates/cdk/src/wallet/proofs.rs:318

[thesimplekid]

Thanks