feat: Add stale PR auto-close workflow

[charlesvien]

Problem

I remember a time when we could regularly hit 0 open PR's on this repo, that seems unlikely to ever happen again (which is a good thing!). The other side of that means we need some automation here so inactivate PRs don't accumulate and clutter the PR list.

Changes

1. Add daily workflow using actions/stale@v9
2. Mark PRs stale after 30 days of inactivity
3. Close stale PRs 7 days later (37 days total)
4. Exempt PRs labeled no stale or security
5. Issues are disabled for now (PR-only), can be enabled later

How did you test this?

I did not

Publish to changelog?

no

[charlesvien]

• feat: Add stale PR auto-close workflow #2386 👈 (View in Graphite)
• main

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[greptile-apps]

T-Rex Logs

What T-Rex did

• Parsed the stale workflow YAML with PyYAML and saved the structured JSON to trex-artifacts/stale-yml-parsed.json; the structure is syntactically valid.
• Looked up actions/stale@v9 README and found it requires issues: write and pull-requests: write, since the action reads both issues and PRs via the REST API.
• Compared the workflow's permissions block, which only grants pull-requests: write, and concluded the action would fail to enumerate items under restricted token permissions, affecting PR listing.
• Verified days-before-issue-stale: -1 and days-before-issue-close: -1 disable staling and closing per docs, but they do not remove the need for the Issues API listing.
• Analyzed exempt-pr-labels: "no stale,security" and noted the comma-split yields ['no stale','security'], with the space-containing name suggesting a potential label mismatch against conventional naming.
• Confirmed exempt-draft-pr: false matches the PR description (drafts are not exempt).
• Did not modify any source; findings are documented in trex-artifacts/stale-workflow-analysis.md.

Artifacts

Parsed stale workflow YAML with PyYAML

• Evidence that the YAML was parsed into structured JSON and saved, showing the parsing outcome and syntactic validity.

Stale workflow permission analysis

• Markdown notes detailing permission requirements, disabled-stale behavior, and label-name observations used to assess workflow feasibility.

_{Ran code and verified through T-Rex}

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
.github/workflows/stale.yml:15-16
**Add issues permission**

`actions/stale` fetches pull requests through the Issues API, and its recommended permissions include both `issues: write` and `pull-requests: write`. With only `pull-requests: write`, this scheduled workflow can fail with a token permission error before it labels or closes any stale PRs, especially in repositories with restricted default workflow permissions.

```suggestion
    permissions:
      issues: write
      pull-requests: write
```

_{Reviews (1): Last reviewed commit: "Add stale PR auto-close workflow" | Re-trigger Greptile}