fix(chain-adapters): prevent UTXO sats/byte rounding to zero

[kaladinlight]

Description

UTXO fee estimation converts satsPerKiloByte (returned by unchained) into the per-byte rate that the coinselect library requires. The conversion used Math.round(satsPerKiloByte / 1000), which collapses any rate below ~500 sats/kB to 0.

This is a real condition during low-fee periods. For example, a recent observation:

slow:    { satsPerKiloByte: 291,  blocksUntilConfirmation: 10 }
average: { satsPerKiloByte: 302,  blocksUntilConfirmation: 5  }
fast:    { satsPerKiloByte: 2227, blocksUntilConfirmation: 2  }

Math.round(291/1000) = 0 and Math.round(302/1000) = 0, so slow/average tiers come back with a 0 per-byte rate. Downstream, buildSendApiTransaction rejects this via if (!satoshiPerByte) throw new Error('satoshiPerByte is required'), breaking the lower-fee tiers entirely.

Fix: use Math.ceil with a 1 sat/byte floor. Math.max(1, Math.ceil(x / 1000)) guarantees a valid positive rate for any non-negative input, and rounding up biases slightly toward inclusion rather than under-paying.

Applied at both UTXO conversion sites:

• packages/chain-adapters/src/utxo/UtxoBaseAdapter.ts (BTC, BCH, LTC, ZEC)
• packages/chain-adapters/src/utxo/dogecoin/DogecoinChainAdapter.ts (DOGE)

The Dogecoin adapter already had a <=0 guard with high default minimums, so it was less likely to trip in practice — but the same math issue applied for any small positive upstream value, and consistency matters.

Issue (if applicable)

closes #

Risk

High Risk PRs Require 2 approvals

What protocols, transaction types, wallets or contract interactions might be affected by this PR?

UTXO chains: BTC, BCH, LTC, ZEC, DOGE. Affects only getFeeData output (slow/average/fast per-byte rates and resulting txFee). No change to signing or broadcasting paths.

The output rate may now be slightly higher than before for the same upstream value (ceil vs round) — by at most ~0.5 sat/byte at the boundary — but this only matters when the upstream rate sits exactly on a half-byte boundary, which is rare.

Testing

Engineering

• Send BTC during a low-fee window (or stub getNetworkFees to return e.g. { slow: 291, average: 302, fast: 2227 }); confirm slow/average/fast tiers all yield positive satoshiPerByte and a valid txFee.
• Send BTC during a normal-fee window; confirm fees are within the same ballpark as before.
• Send DOGE; confirm no regression (per-byte rates remain in expected range).
• Repeat for BCH, LTC, ZEC.

Operations

• 🏁 My feature is behind a flag and doesn't require operations testing (yet)

Screenshots (if applicable)

n/a

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 7bb337fc-e156-4d57-a176-d8f00c9a110f

📥 Commits

Reviewing files that changed from the base of the PR and between 4916056 and d64d0da.

📒 Files selected for processing (6)

• packages/chain-adapters/src/utxo/UtxoBaseAdapter.ts
• packages/chain-adapters/src/utxo/bitcoin/BitcoinChainAdapter.test.ts
• packages/chain-adapters/src/utxo/bitcoincash/BitcoinCashChainAdapter.test.ts
• packages/chain-adapters/src/utxo/dogecoin/DogecoinChainAdapter.test.ts
• packages/chain-adapters/src/utxo/dogecoin/DogecoinChainAdapter.ts
• packages/chain-adapters/src/utxo/litecoin/LitecoinChainAdapter.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/utxo-fee-sats-per-byte-rounding

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