M06-L04 exercise — One discriminating change

Starting checkpoint: CP06. Suggested time: 30–40 minutes.

Capture the original invalid-fixture command, output, and exit. Write two plausible failure locations and a predicted observation that would distinguish them. Inspect the documented grammar and relevant adapter code before changing a file.

Create a separate copied fixture and correct only 28C to 28. Run it, then rerun the unchanged original. Record what both observations establish. Explain why changing the parser to ignore suffixes or replacing the value with zero would answer a different question.

Submit a short fault report containing starting state, reproducer, expectations, hypotheses, chosen test, actual results, correction, and limits. If an assistant drafts the report, review every claim against the preserved evidence. A successful parse does not establish sensor operation, calibration, or physical timing.