# Retrieval Pipeline Identity

A retrieval pipeline is behaviorally identified by:

- embedding-space identity;
- sparse and fusion configuration digests;
- optional reranker deployment and reranker configuration digest;
- candidate-k and output-k semantics.

The canonical identity digest covers every field. An embedding-only control and the same embedding
plus reranker are distinct pipelines even when dimensions and source collection are equal. A
reranker profile/configuration change also creates a new identity. Reranker addition is classified
`behavioral`; an embedding-space change remains `requires_reindex`.

Pipeline comparisons consume immutable fixed-pool runs. They do not overwrite embedding evaluation
runs and cannot be compared as though they were embedding deployments.