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Phase 5 — Bitcoin (reduced custody)

Status: Planned.

Every new BTC payment link becomes a 2-of-2 P2WSH multisig (merchant + platform). Pre-signed refund PSBTs. Platform key moves to HSM/MPC. BTC subscriptions remain out of scope until Lightning BOLT12 recurrence matures.

See Bitcoin considerations for the full reasoning.

Scope​

  • P2WSH descriptor template finalized (wsh(multi(2, ...)) v1, MuSig2/Taproot future).
  • HSM or MPC provider selected for the platform signer.
  • Merchant xpub onboarding in the dashboard.
  • Pre-signed refund PSBT generation + encrypted storage.
  • Co-sign UI for settlement.

Code touched​

Runtime / UX impact​

  • BTC addresses are multisig; Bech32 format for P2WSH.
  • Merchants must onboard a BTC signer to use the non-custodial path. A platform-only fallback exists for 30 days during migration.
  • Payers see a standard BTC address; no change in their flow.
  • Refund can be broadcast any time by the merchant with one click.

Current limitations​

  • No BTC subscriptions (existing limitation; stays true).
  • MuSig2 deferred to v2 once tooling is widely audited.
  • Settlement fee volatility during congestion; CPFP hook available.

Linked blog post​

Phase 5: Bitcoin — Taproot 2-of-2 and Honest Scope

Status checklist​

  • Taproot descriptor template finalized
  • HSM / MPC provider selected
  • Merchant xpub onboarding shipped
  • Per-link descriptor derivation + storage
  • Refund PSBT generation + encrypted storage
  • Settlement co-sign UI shipped
  • Runbook for HSM failover and merchant key loss
  • Canary cohort of merchants on BTC 2-of-2