Each remote repository proxies and caches one external registry per format, on the shared S13 foundation. Scope: - S13 foundation implementation: upstream HTTP client with SSRF covers, Lookup/Probe/Fetch operations, virtual resolution engine, cache freshness, credential handling, health monitoring (spec merged: [S13](https://gitlab.com/gitlab-org/ops/artifact-registry/-/blob/main/docs/specs/S13-virtual-remote-foundation.md)) - Per-format remote slices, spec and implementation each: S14 Maven, S15 npm, S16 container The virtual slices build on these: &22811. Out of scope: the monolith Virtual Registry program (&15088). Spec numbering per the remote/virtual split ([artifact-registry!900](https://gitlab.com/gitlab-org/ops/artifact-registry/-/merge_requests/900)).