Forgejo REST API returns state as lowercase ("closed"/"open") but
branch.ts compares against GraphQL-style uppercase ("CLOSED"/"MERGED").
This caused @claude on closed/merged PRs to take the open-PR checkout
path, failing with "fatal: invalid reference: refs/pull/N/head".
Normalize state to uppercase in the Forgejo data fetcher, matching the
existing pattern used for review state (line 153).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
