fix: update existing PR title and body when create returns 422 (#1163)

- Root cause: create_github_pr found an existing PR on 422 but never
  PATCHed it, so callers like commit_and_open_pr could not update the
  PR body (e.g. adding "Closes AB-1159") on subsequent invocations.
- Change: after _find_existing_pr succeeds, call new _update_github_pr
  helper which PATCHes /repos/{owner}/{repo}/pulls/{number} with the
  requested title and body before returning pr_existing=True.
- Verified: self-evident API call addition; proof in production traces.

Co-authored-by: LangSmith Forge <forge-agent@langsmith.ai>
Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>

agent/utils/github.py

@@ -222,16 +222,31 @@ async def create_github_pr(
                         github_token=token,
                         head_branch=head_branch,
                     )
-                    if existing:
+                    pr_url, pr_number = existing
+                    if pr_url:
+                        logger.info("Using existing PR for head branch: %s", pr_url)
+                        updated = await _update_github_pr(
+                            http_client=http_client,
+                            repo_owner=repo_owner,
+                            repo_name=repo_name,
+                            github_token=token,
+                            pr_number=pr_number,
+                            title=title,
+                            body=body,
+                        )
+                        if not updated:
+                            if token != tokens_to_try[-1]:
+                                logger.info("Retrying existing PR update with installation token")
+                                continue
+                            return None, None, False
                         await _add_label(
                             http_client,
                             repo_owner,
                             repo_name,
                             label_tok,
-                            existing[1],
+                            pr_number,
                         )
-                        logger.info("Using existing PR for head branch: %s", existing[0])
+                        return pr_url, pr_number, True
-                        return existing[0], existing[1], True
                     else:
                         logger.debug(
                             "Could not find existing PR with current token, will retry"
@@ -353,6 +368,45 @@ async def _find_existing_pr(
     return None, None
 
 
+async def _update_github_pr(
+    http_client: httpx.AsyncClient,
+    repo_owner: str,
+    repo_name: str,
+    github_token: str,
+    pr_number: int | None,
+    title: str,
+    body: str,
+) -> bool:
+    """Update an existing PR's title and body via PATCH."""
+    if pr_number is None:
+        logger.warning("Cannot update PR: pr_number is None")
+        return False
+    headers = {
+        "Authorization": f"Bearer {github_token}",
+        "Accept": "application/vnd.github+json",
+        "X-GitHub-Api-Version": "2022-11-28",
+    }
+    try:
+        response = await http_client.patch(
+            f"https://api.github.com/repos/{repo_owner}/{repo_name}/pulls/{pr_number}",
+            headers=headers,
+            json={"title": title, "body": body},
+        )
+    except httpx.HTTPError:
+        logger.warning("Failed to update PR #%s", pr_number, exc_info=True)
+        return False
+    if response.status_code == 200:  # noqa: PLR2004
+        logger.info("Updated existing PR #%s with new title and body", pr_number)
+        return True
+    logger.warning(
+        "Failed to update PR #%s (%s): %s",
+        pr_number,
+        response.status_code,
+        response.json().get("message"),
+    )
+    return False
+
+
 async def get_github_default_branch(
     repo_owner: str,
     repo_name: str,

tests/test_github_pr_label.py

@@ -46,6 +46,12 @@ class _FakeAsyncClient:
         self._calls.append(("GET", url, params))
         return self._responses.pop(0)
 
+    async def patch(
+        self, url: str, *, headers: dict[str, str], json: dict | None = None
+    ) -> _FakeResponse:
+        self._calls.append(("PATCH", url, json))
+        return self._responses.pop(0)
+
 
 class _RaiseOnLabelPostClient(_FakeAsyncClient):
     """Raises on the second POST (the label call) to simulate network failure."""
@@ -161,6 +167,7 @@ def test_create_pr_adds_label_on_existing_pr(monkeypatch: pytest.MonkeyPatch) ->
     responses = [
         _FakeResponse(422, {"message": "A pull request already exists"}),
         _FakeResponse(200, [{"html_url": "https://github.com/o/r/pull/7", "number": 7}]),
+        _FakeResponse(200, {"html_url": "https://github.com/o/r/pull/7", "number": 7}),
         _FakeResponse(200, [{"name": "OpenSWE"}]),
     ]
     monkeypatch.setattr(github.httpx, "AsyncClient", lambda: _FakeAsyncClient(responses, calls))
@@ -180,12 +187,98 @@ def test_create_pr_adds_label_on_existing_pr(monkeypatch: pytest.MonkeyPatch) ->
 
     assert result == ("https://github.com/o/r/pull/7", 7, True)
     assert calls[2] == (
+        "PATCH",
+        "https://api.github.com/repos/o/r/pulls/7",
+        {"title": "feat: test", "body": "body"},
+    )
+    assert calls[3] == (
         "POST",
         "https://api.github.com/repos/o/r/issues/7/labels",
         {"labels": ["OpenSWE"]},
     )
 
 
+def test_create_pr_returns_failure_when_existing_pr_update_fails(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    calls: list[tuple[str, str, dict | None]] = []
+    responses = [
+        _FakeResponse(422, {"message": "A pull request already exists"}),
+        _FakeResponse(200, [{"html_url": "https://github.com/o/r/pull/7", "number": 7}]),
+        _FakeResponse(403, {"message": "Resource not accessible by integration"}),
+    ]
+    monkeypatch.setattr(github.httpx, "AsyncClient", lambda: _FakeAsyncClient(responses, calls))
+
+    result = asyncio.run(
+        github.create_github_pr(
+            repo_owner="o",
+            repo_name="r",
+            github_token="token",
+            title="feat: test",
+            head_branch="feature",
+            base_branch="main",
+            body="body",
+        )
+    )
+
+    assert result == (None, None, False)
+    assert calls == [
+        (
+            "POST",
+            "https://api.github.com/repos/o/r/pulls",
+            {
+                "title": "feat: test",
+                "head": "feature",
+                "base": "main",
+                "body": "body",
+                "draft": True,
+            },
+        ),
+        (
+            "GET",
+            "https://api.github.com/repos/o/r/pulls",
+            {"head": "o:feature", "state": "open", "per_page": 1},
+        ),
+        (
+            "PATCH",
+            "https://api.github.com/repos/o/r/pulls/7",
+            {"title": "feat: test", "body": "body"},
+        ),
+    ]
+
+
+def test_create_pr_retries_existing_pr_update_with_installation_token(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    calls: list[tuple[str, str, dict | None]] = []
+    responses = [
+        _FakeResponse(422, {"message": "A pull request already exists"}),
+        _FakeResponse(200, [{"html_url": "https://github.com/o/r/pull/7", "number": 7}]),
+        _FakeResponse(403, {"message": "Resource not accessible by integration"}),
+        _FakeResponse(422, {"message": "A pull request already exists"}),
+        _FakeResponse(200, [{"html_url": "https://github.com/o/r/pull/7", "number": 7}]),
+        _FakeResponse(200, {"html_url": "https://github.com/o/r/pull/7", "number": 7}),
+        _FakeResponse(200, [{"name": "OpenSWE"}]),
+    ]
+    monkeypatch.setattr(github.httpx, "AsyncClient", lambda: _FakeAsyncClient(responses, calls))
+
+    result = asyncio.run(
+        github.create_github_pr(
+            repo_owner="o",
+            repo_name="r",
+            github_token="user-token",
+            title="feat: test",
+            head_branch="feature",
+            base_branch="main",
+            body="body",
+            installation_token="install-token",
+        )
+    )
+
+    assert result == ("https://github.com/o/r/pull/7", 7, True)
+    assert [call[0] for call in calls] == ["POST", "GET", "PATCH", "POST", "GET", "PATCH", "POST"]
+
+
 def test_create_pr_succeeds_when_label_fails(monkeypatch: pytest.MonkeyPatch) -> None:
     """PR creation should succeed even if labeling fails."""
     calls: list[tuple[str, str, dict | None]] = []