HRF Roadmap: wallet operation endpoints

[Bortlesboat]

Why this matters

Private Bitcoin usage should not require sending wallet construction details through centralized services. Wallet operation endpoints make Satoshi API more useful for self-hosted, local-first Bitcoin workflows.

Scope

Add API support for wallet operations that can be used by local applications and agent tooling.

Acceptance criteria

• Add PSBT construction endpoint or service layer
• Add coin selection support with documented strategy and constraints
• Add multisig-aware request/response shapes where practical
• Keep signing out of scope unless a secure local signing model is explicitly designed
• Document privacy boundaries and what the API does not protect
• Add tests for request validation and representative wallet flows

HRF proposal alignment

This maps to the submitted deliverable: wallet tooling covering PSBT construction, coin selection, and multisig support.