Create comprehensive negative test suite for sig reqs (all operations)

**Summary**
Although `INVALID_SIGNATURE` tests are sprinkled liberally throughout the codebase, it would be valuable to have a single suite that performs negative tests of ops with invalid sigs, followed by extensive state validation.

Start by inventorying the existing INVALID_SIGNATURE tests throughout the codebase and identifying every operation that needs negative coverage. Define the state validations expected after each invalid-signature attempt; done means a single comprehensive suite covers all operations and verifies the resulting state.

Written by the indexing model from the issue text.