Claude GitHub Action fails with exit code 1 despite valid GitHub App token and correct setup

## Summary

Claude GitHub Action starts successfully but consistently fails with exit code 1, even though the setup appears correct and all required tokens are provided.

This does not appear to be a repository misconfiguration.

---

## What works

- Workflow triggers correctly on `issue_comment`
- `@claude` mention is detected
- Claude posts initial comment: "Claude Code is working..."
- Anthropic API key is correctly configured
- GitHub App is created and installed
- Custom GitHub App token is generated and passed explicitly

---

## Workflow

```yaml
name: Claude Code

on:
issue_comment:
types: [created]

jobs:
claude:
if: contains(github.event.comment.body, '@claude')
runs-on: ubuntu-latest
permissions:
contents: write
pull-requests: write
issues: write
id-token: write

steps:
- uses: actions/create-github-app-token@v2
id: app-token
with:
app-id: ${{ secrets.APP_ID }}
private-key: ${{ secrets.APP_PRIVATE_KEY }}

- uses: anthropics/claude-code-action@main
with:
anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
github_token: ${{ steps.app-token.outputs.token }}

Start with the reproduced workflow, especially the `claude` job, the `actions/create-github-app-token@v2` step, and `anthropics/claude-code-action@main`. Run the workflow with the provided setup and inspect the action output around the exit code 1 failure. Done means identifying the action failure and confirming a successful run with the stated token configuration.

Written by the indexing model from the issue text.