Trait BackendRuntime 

pub trait BackendRuntime: Send + Sync {
    type Error: Error + Send + Sync + 'static;

    // Required methods
    fn atomic_opset(&self) -> AtomicOpsetDecl;
    fn dispatch_atomic(
        &mut self,
        op_type: &str,
        inputs: &[(&str, &dyn SlotValue)],
        ctx: &mut RuntimeResourceRef<'_>,
    ) -> Result<DispatchResult, Self::Error>;
    fn materialize_from_wire(
        &self,
        type_hash: u64,
        bytes: Vec<u8>,
    ) -> Result<Box<dyn SlotValue>, BackendMaterializeError>;

    // Provided method
    fn extension_opsets(&self) -> Vec<AtomicOpsetDecl> { ... }
}

Role trait for backend implementations. Universal contract per docs/ROLES.md §2 with no per-role methods (Backend’s role opset is ai.onnx v1 which IS its atomic opset).

Backends MUST minimally cover ai.onnx v1 via atomic_opset. They MAY declare additional opsets (e.g. ai.onnx v17 extensions or custom-domain ops like mybackend.fused.MatMulAdd) via extension_opsets. Node::ready() consults both at build time to verify every NodeProto in the loaded graphs has a covering dispatch entry.

Required Associated Types

type Error: Error + Send + Sync + 'static

Backend-impl-specific error type.

Required Methods

fn atomic_opset(&self) -> AtomicOpsetDecl

Atomic-op opset this impl owns at minimum - ai.onnx v1.

fn dispatch_atomic( &mut self, op_type: &str, inputs: &[(&str, &dyn SlotValue)], ctx: &mut RuntimeResourceRef<'_>, ) -> Result<DispatchResult, Self::Error>

Dispatch a single op or BackendSubgraph carrier. For primitive ops (Add, Mul, …) each arm builds a one-node GraphProto and calls Backend::execute. For the BackendSubgraph op_type, the embedded GraphProto body rides on the carrier NodeProto’s "body" attribute and the derive arm calls Backend::dispatch so user overrides (caching, async) reach the engine.

fn materialize_from_wire( &self, type_hash: u64, bytes: Vec<u8>, ) -> Result<Box<dyn SlotValue>, BackendMaterializeError>

Engine-side bridge for Backend::materialize_from_wire. The derive forwards (type_hash, bytes) through the user’s Contract method and re-boxes the typed Self::Tensor into a [BackendTensorCarrier] wrapped in Box<dyn SlotValue> so the engine can install it in the slot table without knowing the backend’s concrete tensor type. Returns BackendMaterializeError on backend error; the engine surfaces this as crate::bus::WireReceiveErrorKind::BackendMaterializeFailed.

Library makers do not implement this method — #[derive(bb::Backend)] emits the bridge.

Provided Methods

fn extension_opsets(&self) -> Vec<AtomicOpsetDecl>

Additional opsets this backend supports beyond atomic_opset. Default empty - backends that ship pure ai.onnx v1 need not override.

Examples of valid extensions:

• A newer ai.onnx version ((ai.onnx, 17)) declaring ops absent from v1.
• A custom-domain opset ((mybackend.fused, 1)) the backend recognizes via its dispatch_atomic body.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors