Round 2 verification audit for C049

Model: gpt-5

Claim: The 16 error operators are M_{i,j} = exp(-i (pi/2) sigma_{i,down e} tensor sigma_{j,down e}) with i,j in {0,x,y,z} (sigma_0=I), defined local when i=0 or j=0 and global otherwise.

Source alignment: source/supp_content.tex:60-64 (Supp. Mat. S2)

Prior official verdict: verified with failure_reason None.

Executable evidence: run.py. Sandbox rerun logs: run.log.

Independent audit: I audited the false-looking R001/R002 VERDICT_OK=False. The failing check asks every basis state containing |up> to be invariant, but that is not a property of local channels when sigma_0 is the full identity. For example I tensor X should leave the first ion unchanged and flip the second ion if it is in |down>. The code nevertheless verifies the operator definitions, unitarity, down/e block action, and local/global count. I correct the note and keep verified.

Decision: Round 2 verdict is verified with failure_reason None and limitations []. Notes: Round-2 audit corrects an overbroad round-1 note while preserving the verified verdict. The script verifies all 16 M_{i,j}=exp[-i(pi/2) sigma_i tensor sigma_j] are finite and unitary, their {down,e}^{otimes2} block equals -i sigma_i tensor sigma_j, and the local/global count is 7 local (i=0 or j=0, including identity) and 9 global. The old statement that every |up>-containing basis state is invariant is false for local channels such as I tensor X; that property is not part of the claim. The operator definition and classification claimed in the paper are verified.