Provider Cache Archive Dir Race

Fixed a race condition that left cached provider archives in the working directory

With the provider cache server enabled via --provider-cache, a race let the server start responding to requests before it had finished preparing the directories it caches into. A provider requested in that window had its archive and lock file written relative to the working directory instead of into the cache, leaving zip files behind in your project.

That race condition has been fixed. Providers now always download into the cache directory.