This is the fifth field test in my Scarab Diagnostic Suite series, and it is the most significant one so far.
The target was a long-running issue in Terraform core:
hashicorp/terraform #32901
The issue has been open since 2023 and centers around shared provider cache behavior. On the surface, it looks like a permissions problem: Terraform attempts to use a shared provider cache, but under certain conditions it tries to write into that cache and fails with errors like:
permission denied
or:
operation not permitted
But the field test suggested something deeper.
This was not only about file permissions.
It was about provider cache authority.
The broad shape
Terraform provider installation involves several sources of truth:
the provider cache,
the dependency lock file,
the selected provider version,
the provider checksum,
the local working directory,
and the filesystem’s ownership rules.
The failure appears when those authorities do not line up cleanly.
In other words, the cache may be readable and the provider may already exist, but Terraform may still decide it needs to install or reconcile the provider in a way that attempts to mutate the shared cache.
That is where the permission failure becomes visible.
The field test
Using Scarab Diagnostic Suite, I treated this as a source-of-truth boundary problem rather than a simple chmod problem.
The first proof reproduced the behavior across Terraform versions and showed that the compatibility escape hatch changed the outcome.
The stronger proof used a Linux two-user/group shared-cache setup:
one user populated the shared provider cache,
another user in the same group consumed it,
the cached provider was visible and executable,
but Terraform 1.4+ could still enter a path that tried to write into the shared cache and failed.
The important discovery was that Terraform succeeds when the cached provider is sufficiently confirmed by lock/checksum authority.
It fails when Terraform decides it must install or reconcile the provider into the global cache, even though that cache is shared and not safely writable by the current user.
That makes the visible permissions error a symptom of a deeper authority boundary.
Candidate repair
A narrow candidate repair was tested locally.
The repair does not blindly trust the cache.
It does not bypass checksum safety.
It does not make a shared cache magically writable.
Instead, the candidate behavior is:
When a warm global cache package exists but Terraform cannot treat it as fully confirmed provider truth, do not overwrite the global cache entry. Install into the local working cache instead.
That keeps the global cache as a readable source while keeping mutation local.
The important safety boundaries still held in the local test:
matching lock state still used the shared cache,
wrong same-version checksum still failed,
the no-lock warm-cache case no longer failed by trying to mutate a shared cache entry owned by another user.
The focused provider-cache tests passed, and the Linux two-user reproduction passed with the candidate repair.
Why this matters
This is the strongest Scarab field test so far because it moved from symptom to architecture.
The surface symptom was:
permission denied
The deeper issue was:
provider cache authority, lock/checksum authority, and filesystem ownership authority were not aligned.
That is the kind of thing Scarab Diagnostic Suite is being built to identify.
Not just:
“Where did the command fail?”
But:
“What boundary did the failure expose?”
This matters because infrastructure software often fails at the point where hidden assumptions meet real-world scale.
Shared caches, CI runners, filesystem mirrors, provider locks, and parallel workflows are not edge abstractions. They are how serious teams operate.
A small cache authority problem can become a large operational problem when repeated across many users, many projects, or many CI jobs.
Field test result
Field Test #005
Project: Terraform core
Issue: hashicorp/terraform #32901
Surface: provider cache authority boundary
Result: reproduced the failure, identified the broader cache/lock/filesystem authority shape, tested a narrow candidate repair, and preserved checksum safety in the local proof.
This is not a claim that the upstream project has accepted the repair.
It is a field-test result.
And as a Scarab Diagnostic Suite test, it matters because it shows the system doing what it is supposed to do:
take a messy long-running failure,
find the boundary underneath it,
prove the failure in a controlled reproduction,
and guide a bounded repair candidate without turning the whole repo into a patch surface.
That is professional diagnostic engineering.
That is the point of Scarab.
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