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Against focas-mock: - H15: a local TCP relay in front of the shared mock takes "the CNC" away and brings it back without stopping the fixture. A FIXED-only driver goes Degraded with LastSuccessfulRead frozen and its value Bad, then returns to Healthy with Good values (the positive control). - H20: the mock answers cnc_rdalmmsg2 in the 80-byte legacy layout. Nineteen alarms (1,520 B = 20 x 76) now decode as the 19 seeded alarms; the old length test gives 20, verified red. A 3-alarm reply is the control. Refs #740 Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT