Function stream_progress_cache_key 

pub(super) fn stream_progress_cache_key(cache_key: &str) -> String

Cache key for the checkpoint sidecar, keyed alongside the geometry and metadata entries for the same request.

v1 is { total_jobs, after_batch }. Bump on any change to what those numbers mean; an entry that fails to deserialize is treated as absent, so a bump degrades to the mesh-unit fallback rather than to garbage.