forge-multisig — add test verifying cancel() by non-proposer only succeeds when threshold is mathematically unreachable

[Austinaminu2]

Summary

cancel() allows non-proposer owners to cancel only when remaining_possible < threshold. There is no test verifying the boundary: exactly at the boundary (cannot cancel) vs one rejection past it (can cancel).

Tasks

• Set up a 3-of-5 multisig
• o1 proposes (1 approval, 0 rejections, 4 remaining possible — threshold reachable)
• o2 rejects (1 approval, 1 rejection, 3 remaining — still reachable)
• o3 rejects (1 approval, 2 rejections, 2 remaining — still reachable, 1+2=3 = threshold)
• o4 attempts cancel() — assert Err(MultisigError::CannotCancel) (2 remaining == threshold)
• o4 rejects (1 approval, 3 rejections, 1 remaining < threshold of 3)
• o5 calls cancel() — assert success
• Verify proposal.cancelled == true

Labels: testing, forge-multisig