Multi-sig Vault (Hard)

Model a vault with M-of-N approvers. Support create proposal, approve, execute, and cancel flows.

API sketch

POST /api/vaults — Create vault with signer pubkeys and threshold M

POST /api/vaults/:id/proposals — Create transfer proposal

POST /api/vaults/:id/proposals/:pid/approve — Record approval from a signer

POST /api/vaults/:id/proposals/:pid/execute — Execute when threshold met and timelock elapsed

Return 403 for unauthorized signers and 409 for invalid state transitions.