Bun: Internal error 'directory mismatch for directory' in v1 action on GitHub-hosted runners

## Summary

Every invocation of `anthropics/claude-code-action@v1` from our repo's `review` workflow fails with a Bun internal error during action setup:

```
Internal error: directory mismatch for directory "/home/runner/work/_actions/anthropics/claude-code-action/v1/tsconfig.json", fd 4
```

The error comes from Bun (the runtime the action uses); no user code runs. It reproduces on every PR in our repo.

## Reproduction

A reproducing run from PR #10526 in our repo (trajectory-labs-pbc/agent-c):
https://github.com/trajectory-labs-pbc/agent-c/actions/runs/24585295927/job/71893230564

The failure occurs in the `review` job, during action setup, before any user inputs are consumed.

## Impact

`review` jobs fail on every PR, blocking green CI for repos that require all checks to pass.

## Environment

- Runner: `ubuntu-latest` (GitHub-hosted)
- Action ref: `anthropics/claude-code-action@v1`
- Our repo: public, standard PR-triggered workflow

## Ask

- Pin Bun to a known-good version inside the action, or
- Surface a more actionable error if this is a repo- or path-specific issue, or
- Advise on a workaround we can apply from the caller side.

Happy to provide more logs on request.

Start with the linked PR #10526 workflow run and the `review` job setup failure at `/home/runner/work/_actions/anthropics/claude-code-action/v1/tsconfig.json`. Inspect the Bun runtime used by `anthropics/claude-code-action@v1` and reproduce the directory-mismatch error on `ubuntu-latest`. Done means identifying a reliable action-side fix, actionable error, or caller-side workaround that lets the review job complete.

Written by the indexing model from the issue text.