Function merge_embedding_mutation_batch 

pub fn merge_embedding_mutation_batch<C>(
    project_dir: &Path,
    manifest: &EmbeddingGenerationManifest,
    batch: EmbeddingMutationBatch<'_>,
    limits: EmbeddingMutationJournalLimits,
    coordination: SearchCoordinationLimits,
    checkpoint: C,
) -> Result<EmbeddingMutationJournal, SearchArtifactError>
where
    C: FnMut() -> Result<(), SearchArtifactError>,

Merge one relevant committed batch without losing the prior durable journal.