Cas Local Source Cache Dirs

CAS handles local sources that have already been initialized

With CAS enabled, reading a local source that had already been initialized failed and fell back to the slower standard copy. Generating a stack from such a unit logged CAS processing failed ... source escapes repository root.

Provider caching was the cause. Both the Provider Cache Server and the Automatic Provider Cache Dir leave the plugins under .terraform pointing into a shared cache outside the source. CAS read those links as the source reaching outside itself and refused to copy the link for safety.

CAS now leaves .terraform and .terragrunt-cache out of local sources, keeping .terraform.lock.hcl and everything else. OpenTofu, Terraform, and Terragrunt rebuild both directories on demand, so units and stacks no longer receive a stale copy of either. Running tofu init in a source directory no longer changes that source's CAS key.