Give retained stream policies consistent concrete identity

Parent

Different bounds and refetch policies cannot satisfy each other from incompatible cached histories.

Include normalized maxChunks and refetchMode in concrete accumulated-stream identity; omitted values normalize to unlimited/reset.
Key/options builders agree; default key calls remain usable and explicit defaults equal omitted defaults.
Verify wide-to-narrow and narrow-to-wide fetches, concurrent views, refetch behavior, and invalid policy handling including skipped queries.
Preserve concrete DataTags and root/branch/leaf/streamed-operation invalidation prefixes.
Publish matching compile-time fixtures and document the current cache-identity contract without exposing an internal tuple layout.