[HARD][MULTISIG] Bind approvals to signer epochs and preserve reachable quorum

[Obiajulu-gif]

Problem

Pending approvals can survive signer-set changes, allowing stale signers to count or leaving thresholds unreachable.

Scope

• Add a monotonically increasing signer epoch and signer-set hash.
• Bind proposals and approvals to an epoch with an explicit snapshot/invalidation rule.
• Prevent removed signers and stale approvals from later epochs.
• Validate every signer/threshold change for reachable quorum.
• Add expiry, cancellation, idempotent execution, and replay-resistant IDs.
• Govern signer changes after bootstrap.
• Emit events sufficient for external reconstruction.

Acceptance criteria

• Approval validity is unambiguous across rotations.
• Threshold never exceeds eligible signers.
• Duplicate approvals never increase quorum.
• Terminal proposals cannot revive.
• Bootstrap authority is permanently constrained.
• UI explains epoch and counted approvals.

Required tests

Add/remove/rotate around partial approval, threshold changes, removed/re-added signer, concurrent final approval/rotation, and random governance sequences.

Non-goals

Harden native governance; no external DAO required.

[fhayvy]

Hi maintainer, please assign this issue to me. I would love to contribute.

[grantfox-oss]

🦊 GrantFox — @fhayvy has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #31)
2. Your PR will be reviewed by the Vaultquest maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@fhayvy's PR #80 was approved and merged by @BigDella.

🏆 @fhayvy: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (642 total points). Track your full progress on GrantFox.

👏 Great work, @fhayvy! Keep contributing to Vaultquest.