fix: handle existing pull request error in create_pull_request to prevent crash

aider_gitea/gitea_client.py

@@ -166,6 +166,20 @@ class GiteaClient:
         }
 
         response = self.session.post(url, json=json_data)
+        # If a pull request for this head/base already exists, return it instead of crashing
+        if response.status_code == 422:
+            logger.warning(
+                "Pull request already exists for head %s and base %s", head, base
+            )
+            prs = self.get_pull_requests(owner, repo)
+            for pr in prs:
+                if (
+                    pr.get("head", {}).get("ref") == head
+                    and pr.get("base", {}).get("ref") == base
+                ):
+                    return pr
+            # fallback to raise if we can’t find it
+            response.raise_for_status()
         response.raise_for_status()
         return response.json()
 
@@ -182,3 +196,15 @@ class GiteaClient:
         response = self.session.get(url)
         response.raise_for_status()
         return response.json()
+
+    def get_pull_requests(
+        self,
+        owner: str,
+        repo: str,
+        state: str = "open",
+    ) -> list[dict]:
+        """Fetch pull requests for a repository."""
+        url = f"{self.gitea_url}/repos/{owner}/{repo}/pulls?state={state}"
+        response = self.session.get(url)
+        response.raise_for_status()
+        return response.json()