Fix Claude checkout issue for forked PRs

- Add environment overrides to prevent PR branch checkout
- Add explicit github_token for authentication
- Add direct_prompt to guide Claude to use diff file
- Override GITHUB_REF and GITHUB_SHA to stay on base branch

.github/workflows/claude-review-fork.yml

@@ -142,12 +142,24 @@ jobs:
         id: claude
         uses: anthropics/claude-code-action@beta
         timeout-minutes: 15
+        env:
+          # Override to prevent checkout of PR branch
+          GITHUB_REF: refs/heads/${{ github.event.repository.default_branch }}
+          GITHUB_SHA: ${{ github.event.pull_request.base.sha || github.sha }}
         with:
           claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           
+          # Explicitly provide GitHub token
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          
           # Trigger phrase for manual reviews
           trigger_phrase: "@claude-review-fork"
           
+          # Tell Claude to analyze the diff file instead of checking out code
+          direct_prompt: |
+            IMPORTANT: Analyze the pr-diff.patch file that has already been created in the current directory.
+            Do NOT attempt to checkout any code. The diff file contains all the changes you need to review.
+          
           # Custom instructions for fork review
           custom_instructions: |
             You are performing a CODE REVIEW ONLY for a PULL REQUEST FROM A FORK. You cannot make any changes to files.