Multisig contract suite

🧐 Motivation

Institutional use cases need a multisig primitive on Midnight that gates shielded operations on M-of-N ECDSA threshold authorization, so off-chain HSM co-signers can participate using the same signing infrastructure they already use on EVM chains — without running a proof server, holding coin secret material, or leaking shielded balances onto the public ledger. Midnight's native shielded model has no such primitive today.

📝 Details

Umbrella issue tracking the multisig contract suite. The suite composes generic primitives (signer registry, treasuries, presets) into deployment-specific topologies — typically one token contract per issuer, one vault per custodian, and one forwarder per end-recipient.

Primary blocker: ECDSA + Keccak primitives in Compact. Until both land, signature verification is stubbed and stateless presets cannot be deployed to production.