ci: prevent duplicate PR check from flagging current PR as duplicate (#6924)

Co-authored-by: Aiden Cline <aidenpcline@gmail.com>

.github/workflows/duplicate-prs.yml

@@ -44,6 +44,8 @@ jobs:
           {
             echo "Check for duplicate PRs related to this new PR:"
             echo ""
+            echo "CURRENT_PR_NUMBER: $PR_NUMBER"
+            echo ""
             echo "Title: $(gh pr view "$PR_NUMBER" --json title --jq .title)"
             echo ""
             echo "Description:"

.opencode/agent/duplicate-pr.md

@@ -12,6 +12,8 @@ You are a duplicate PR detection agent. When a PR is opened, your job is to sear
 
 Use the github-pr-search tool to search for PRs that might be addressing the same issue or feature.
 
+IMPORTANT: The input will contain a line `CURRENT_PR_NUMBER: NNNN`. This is the current PR number, you should not mark that the current PR as a duplicate of itself.
+
 Search using keywords from the PR title and description. Try multiple searches with different relevant terms.
 
 If you find potential duplicates:

.opencode/tool/github-pr-search.ts

@@ -45,6 +45,11 @@ export default tool({
     }
 
     const prs = result.items as PR[]
+
+    if (prs.length === 0) {
+      return `No other PRs found matching "${args.query}"`
+    }
+
     const formatted = prs.map((pr) => `${pr.title}\n${pr.html_url}`).join("\n\n")
 
     return `Found ${result.total_count} PRs (showing ${prs.length}):\n\n${formatted}`