fix: retry plugin cache errors in terraform_validate

[AruneshDwivedi]

When TF_PLUGIN_CACHE_DIR is used with parallelism (from #620), concurrent terraform validate processes can corrupt the plugin cache, causing intermittent failures.

I kept hitting this in our CI where multiple pre-commit hooks run in parallel. The errors look like:

could not retrieve the list of available versions for provider
unexpected value returned by API
plugin is cached but contents have changed
the plugin cache directory is invalid

All of these go away on retry. The existing --retry-once-with-cleanup flag already handles retrying after clearing .terraform/modules and .terraform/providers -- these errors just weren't in the match list.

This PR adds them to match_validate_errors in hooks/terraform_validate.sh. That's the same function that already catches "Module source has changed", "Could not load plugin", etc. No other changes to the init or validate flow.

After adding these patterns, our CI runs pass consistently without the 2-3 retries we were seeing before.

Related to #640

[coderabbitai]

📝 Walkthrough

Walkthrough

The match_validate_errors function in hooks/terraform_validate.sh gains four new case patterns that classify provider version list API failures, unexpected API value responses, provider cache-content changes, and an invalid plugin cache directory as retryable errors (returning 1), prompting per_dir_hook_unique_part to clear cached Terraform state and re-run terraform validate.

Changes

Retryable Error Pattern Expansion

Layer / File(s)	Summary
New retryable case patterns in match_validate_errors hooks/terraform_validate.sh	Adds four case branches that return 1 for provider version list API failures, unexpected API value responses, provider cache-content changes, and invalid provider plugin cache directory errors, making them trigger the existing retry logic.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title 'fix: retry plugin cache errors in terraform_validate' directly and clearly summarizes the main change - adding retry logic for plugin cache-related errors in the terraform validation script.
Description check	✅ Passed	The description provides detailed context about the plugin cache race condition, lists the specific error patterns being handled, explains the fix mechanism, and relates it to existing functionality and related issues.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[MaxymVlasov]

https://github.com/antonbabenko/pre-commit-terraform/blob/master/.github/AI_POLICY.md#slop