Vault Construction and Coordination Transport

Bitcoin custody discussion routinely treats two independent questions as one: which spending paths exist and under which conditions the chain enforces them, and how the humans and devices holding shares of those paths exchange the bytes that build a valid transaction. This paper separates the two layers, examines a serious example of each, B-SSL as a covenant-free Taproot vault construction and PSBT coordination over Nostr relays as a transport, and argues that the security claims of a custody system are the composition of both. It closes with the open problems that stand between the transport sketch and a deployable specification.

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• Version 1.031 August 2026First publication. Co-published by Custody Agents and BitVault.

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