Add _base equipment-class template for universal cross-machine metadata that every machine in the OtOpcUa estate exposes regardless of vendor, protocol, or machine type. References OPC UA Companion Spec OPC 40010 (Machinery) for the Identification component (Manufacturer, Model, ProductInstanceUri, SerialNumber, HardwareRevision, SoftwareRevision, YearOfConstruction, ManufacturerUri, DeviceManual, AssetLocation) plus the MachineryOperationMode enum (Auto, Manual, Maintenance, Service, Setup, Other), OPC UA Part 9 for the alarm summary fields (HasActiveAlarms, ActiveAlarmCount, HighestActiveAlarmSeverity), ISO 22400 for the lifetime counter fields (TotalRunSeconds, TotalCycles) that feed Availability + Performance KPIs at Layer 3, and the 3-year-plan handoff §"Canonical Model Integration" for the canonical state vocabulary (Running / Idle / Faulted / Starved / Blocked) declared in _base.stateModel. Includes the OtOpcUa five-identifier set (EquipmentUuid, MachineCode, ZTag, SAPID, plus DeviceClass = EquipmentClassRef) so every machine surfaces the join keys downstream consumers need; ConnectionState + LastDataTimestamp + DriverType for driver-side observability that does not require any particular equipment-protocol feature; optional production context (CurrentWorkOrder, CurrentPartNumber, CurrentRecipe, CurrentOperator, CurrentShift) marked isRequired: false since not every machine type surfaces these. Plus two universal alarm definitions (communication-loss, data-stale) that apply to every equipment regardless of class.

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>

schemas/format/equipment-class.schema.json

@@ -9,8 +9,13 @@
   "properties": {
     "classId": {
       "type": "string",
-      "pattern": "^[a-z0-9-]{1,64}$",
-      "description": "Stable logical ID for the class. Lowercase, hyphens allowed. Once published, never changes — clients pin to it."
+      "pattern": "^[a-z0-9-_]{1,64}$",
+      "description": "Stable logical ID for the class. Lowercase, hyphens, underscores allowed. Once published, never changes — clients pin to it. Convention: `_` prefix indicates an abstract base class (e.g. `_base`) intended only to be extended, not used directly on equipment."
+    },
+    "extends": {
+      "type": ["string", "null"],
+      "pattern": "^[a-z0-9-_]{1,64}$",
+      "description": "Optional parent class to inherit from. Inherited signals, alarms, and stateModel are merged into this class — the child can add new ones and override individual entries by `name`. The `_base` class (which every equipment template should extend) provides the universal cross-machine metadata (identity, state, alarms, optional production context)."
     },
     "version": {
       "type": "string",