### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

The `Check Duplicate Issues` workflow fails on every `issues` event. The `check-duplicate` job runs `.github/scripts/close_duplicate_issues.py`, which exits 1 with a `json.decoder.JSONDecodeError: Unterminated string starting at: line 1 column 1043331 (char 1043330)` while fetching the open issue list.

The root cause is in `fetch_open_issues`. It runs `gh api --paginate` and then parses the output with `for line in raw.strip().splitlines(): json.loads(line)`. That assumes `gh --paginate` emits one complete JSON array per line, but `gh --paginate` concatenates pages of JSON without a guarantee that each physical line is a self-contained JSON document. Once the combined output is large enough (the repo now has enough open issues that the payload exceeds ~1 MB), `splitlines()` yields a line that is a truncated, unterminated JSON fragment and `json.loads` raises. The duplicate-detection and auto-close step never runs.

A robust fix is to not rely on line splitting: either use `gh api --paginate --slurp` (which emits a single well-formed JSON array…