Equipment-class.schema.json gains an `extends` field for class inheritance — child classes inherit signals, alarms, and stateModel from the parent and can add new ones or override individual entries by name. Convention: `_` prefix on classId marks an abstract base class (e.g. `_base`) intended only to be extended, not assigned directly to equipment via Equipment.EquipmentClassRef.
FANUC CNC class updated to extends: "_base"; redundant identity signals (Version, ActiveAlarmCount) removed since they're now in the base; remaining FANUC-specific signals updated with cross-references showing how they feed into the base signals at Layer 3 (RunState → canonical Running/Idle/Faulted derivation; AlarmActive → HasActiveAlarms / HighestActiveAlarmSeverity; PartsCount → TotalCycles; MainProgramNumber → CurrentRecipe).
Format-decisions.md adds D9 (rationale for `_base` + `extends` inheritance, with references to OPC 40010 / Part 9 / ISO 22400 / handoff) and D10 (signal `category` drives OPC UA folder placement, per OPC 40010 Identification + Status pattern, with a category-to-folder mapping table).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>