pytyche.bcf.hurdle.orchestration

Hurdle BCF chunk machinery and PPC summary.

These are internal helpers used by the joint hurdle MCMC orchestrator.

The module-level _chunk_fn_cache dict holds JIT-compiled chunk functions keyed by (n, hyperparams, freeze_gamma, sev_weight) tuples. Keyed lookups avoid re-tracing the JAX scan across chunks with identical config.

The cache key includes retain_topology_history so a fit with retention on compiles to a separate XLA variant; default-off code paths inherit the same key shape with byte-identical XLA codegen.

_single_chain_step lives at pytyche.bcf.hurdle.model; it is imported lazily inside _make_chunk_fn to avoid a circular import (model.py imports orchestration.py for _run_chunk / _run_sampling_chunk).