chore: establish hwlab l0 contract skeleton

protocol/capabilities.md

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+# Capability Model
+
+Box hardware is described with resources and capabilities.
+
+## Resource
+
+A box resource is a physical or simulated component that can be addressed by
+the gateway:
+
+- board
+- power supply
+- serial port
+- network port
+- relay
+- sensor
+- simulator endpoint
+
+Resources carry lifecycle state such as `available`, `reserved`, `running`,
+`maintenance`, or `offline`.
+
+## Capability
+
+A capability describes an action or measurement exposed by a resource. Examples:
+
+- `power.cycle`
+- `power.set_voltage`
+- `serial.console`
+- `network.link`
+- `firmware.flash`
+- `sensor.read`
+
+Capabilities declare:
+
+- direction: `input`, `output`, or `bidirectional`
+- value type: `boolean`, `integer`, `number`, `string`, `object`, or `binary`
+- optional unit
+- constraints for allowed values or ranges
+- whether the operation mutates hardware state
+
+## Operation Binding
+
+Hardware operations reference capabilities by `capabilityId` and resources by
+`resourceId`. Implementations must not infer a capability from a free-form
+operation name when a capability record exists.