Support Low-Fee Relay in Bitcoin Core (0.1 sat/vB) #404
Description
Bitcoin Core v29.1 lowered the default mempoolminfee to 0.00000001 BTC/kvB (0.1 sat/vB = 25 sat/kw), making low-fee transactions relayable by default nodes.
PeerSwap currently enforces a fee floor around 253 to 275 sat/kw in onchain/bitcoin.go and onchain/estimator.go, which prevents offering sub-1 sat/vB fees.
Proposal
- Make fee floors version-dependent by default:
- v29.2+ default floor: 25 sat/kw (0.1 sat/vB).
- Older versions default floor: 253 sat/kw (about 1 sat/vB).
- Apply the same logic for any fallback fee path to keep behavior consistent with the estimator.
Scope
Bitcoin on-chain path only; Liquid and other chains remain unchanged.
Acceptance Criteria
- With Bitcoin Core v29.2+, the fee floor used by PeerSwap is 25 sat/kw.
- With pre-v29.2 and no overrides, the fee floor is 253 sat/kw.
- Estimator and fallback logic consistently respect the same floor.
Risks and Considerations
Nodes with custom mempoolminfee may differ from version-based defaults; we prefer version-aware defaults over live mempoolminfee to keep behavior predictable. Document this clearly.