Backend extensions

ZADU 0.5.1 introduced the provisional zadu.backends entry-point group. An external package registers one unique lowercase backend name and points it at a factory:

[project.entry-points."zadu.backends"]
my_backend = "my_zadu_backend:create_provider"

The callable receives the normalized ExecutionConfig and returns an exact resource provider implementing the protocol in zadu.backends.base. Its name must equal the entry-point name and exact must be True.

def create_provider(execution):
    return MyExactProvider(
        device=execution.device,
        dtype=execution.resolved_dtype,
    )

An accelerator that needs planner-owned scratch memory may implement:

def working_memory_bytes(self, key, n_samples, available_bytes):
    ...

Return a positive integer for resources handled by the provider and None for resources that need no provider-specific plan. The value participates in the preallocation guard and is passed back to build()/build_batch().

External providers must preserve stable self exclusion and duplicate-distance tie behavior, fall back explicitly for unsupported exact resources, keep score results unchanged, and put execution details only in diagnostics. The entry point API is provisional in 0.5.x; providers should pin the ZADU minor series they test against.