Function validate_distributed_content_dag 

pub fn validate_distributed_content_dag(
    model: &ModelEnvelope,
    realization: &RealizationEnvelopeV1,
    run: &RunManifestV2,
    system: &LinearSystemEnvelopeV1,
    partition: &PartitionEnvelopeV1,
    layout: &DistributedLayoutEnvelopeV1,
) -> Result<DistributedLinearSystem, Diagnostic>

Validate the external links in one distributed spatial artifact content DAG.

This check proves exact content linkage from the run through its Realization and Model, and from that Realization through the distributed layout to its complete system and unique-owner partition. The returned system is freshly reconstructed from the linked complete algebra and owner map; callers can reuse it for later admission instead of deriving the layout a second time.

This artifact-layer check deliberately does not prove that system was lowered from model under realization. Semantic derivation replay belongs in the public facade integration, where the canonical lowerer is available. In particular, the admitted spatial dimension is not the algebraic degree- of-freedom count and can only be rechecked against the replayed mesh and lowering, while this function proves the system/partition algebraic dimension agreement.

Errors

Returns EQ0901 if any content identity, typed model identity, semantic revision, distributed requirement, algebraic shape/scalar, derived layout, execution partition count, target, worker count, or reduction policy is inconsistent.