Commit 2026-10-02 13:43 2d1b80eb

ci: restore the DownstreamTest cache check (#44409) #20532 added a CI step that fetches the cache from DownstreamTest/, a minimal project that requires mathlib, and checks that lake build --no-build Mathlib succeeds there. #26590 removed that step, and #44357 removed the last remaining setup for it, so DownstreamTest/ is currently unused. This PR restores the check as a step in the post_steps job, after the existing cache verification. It covers the cache tool's downstream-only toolchain and manifest checks, fetching the dependencies' oleans into a downstream project's .lake/packages/, and Lake accepting the cached oleans in a dependency context. The step is skipped when the verification step finds that a fork PR changed the cache key space, since the downstream check would miss for the same reason.