fix(scripts): preserve existing labels when auto-closing duplicate issues

[AliAltivate]

What

scripts/auto-close-duplicates.ts closes each detected duplicate with a single PATCH /repos/{owner}/{repo}/issues/{n}:

{
  state: 'closed',
  state_reason: 'duplicate',
  labels: ['duplicate']   // replaces the issue's ENTIRE label set
}

Per GitHub's REST API, the Update an issue endpoint's labels field replaces the full label set — docs: "Pass one or more labels to replace the set of labels on this issue."

So every issue auto-closed as a duplicate has all of its other labels silently wiped (bug, area:*, platform:*, priority, needs-info, …), leaving only duplicate. That destroys triage/analytics metadata on closed issues. This script runs in .github/workflows/auto-close-duplicates.yml.

The fix

Add the duplicate label with the Add labels to an issue endpoint (POST /issues/{n}/labels), which appends to the existing labels — docs: "the labels to add to the issue's existing labels" — and drop labels from the PATCH so it only closes the issue and sets state_reason: 'duplicate':

// append — preserves existing labels
POST  /repos/{owner}/{repo}/issues/{n}/labels   { labels: ['duplicate'] }
// then close
PATCH /repos/{owner}/{repo}/issues/{n}          { state: 'closed', state_reason: 'duplicate' }

The label is added before the close so a partial failure leaves the issue open and retryable, rather than closed without its triage metadata.

Verification

• The clobber was the only labels reference in the file — single-site change.
• Transpiles cleanly under bun (the script's runtime).
• Behavior is grounded in the two official GitHub REST endpoints linked above (replace vs. append). The script mutates production issues, so it isn't run live here; the fix relies on documented endpoint semantics.

🤖 Generated with Claude Code