diff --git a/scripts/publish_zhenxun.py b/scripts/publish_zhenxun.py
index 0a51b2a..c00e614 100644
--- a/scripts/publish_zhenxun.py
+++ b/scripts/publish_zhenxun.py
@@ -59,12 +59,13 @@ def publish(package, confirmed=False, request=None):
     parent = ref["object"]["sha"] if ref else None
     if parent:
         owned = call("GET", f"contents/FARM-MANIFEST.json?ref={BRANCH}", None)
-        if not owned or owned.get("encoding") != "base64":
-            raise ValueError("Existing preview branch is not generated by Farm")
-        previous = json.loads(base64.b64decode(owned["content"]))
-        if (previous.get("target") != "zhenxun"
-                or previous.get("plugin") != manifest["plugin"]):
-            raise ValueError("Existing preview branch ownership differs")
+        if owned is not None:
+            if owned.get("encoding") != "base64":
+                raise ValueError("Existing Farm manifest encoding is invalid")
+            previous = json.loads(base64.b64decode(owned["content"]))
+            if (previous.get("target") != "zhenxun"
+                    or previous.get("plugin") != manifest["plugin"]):
+                raise ValueError("Existing preview branch ownership differs")
     tree = []
     for name, content in sorted(files.items()):
         blob = call("POST", "git/blobs", {
diff --git a/tests/test_zhenxun_package.py b/tests/test_zhenxun_package.py
index ce4060a..774c67f 100644
--- a/tests/test_zhenxun_package.py
+++ b/tests/test_zhenxun_package.py
@@ -230,20 +230,38 @@ class ZhenxunPackageTests(unittest.TestCase):
             with self.assertRaisesRegex(ValueError, "not accessible"):
                 publish(package, True, lambda *args: None)
 
-    def test_symlink_duplicate_and_unmanaged_branch_rejected(self):
+    def test_publish_replaces_unmanaged_main_and_preserves_history(self):
         from publish_zhenxun import publish
-        from zipfile import ZipInfo
+        from verify_zhenxun import read_package
         package, _ = self.clean_package()
-        with patch.dict("os.environ", {"FARM_RELEASE_TOKEN":"unit-test"}):
-            def unmanaged(method, path, data):
-                if path == "":
-                    return {"default_branch": "main"}
-                if path.startswith("git/ref/"):
-                    return {"object": {"sha": "existing"}}
-                return None
+        calls = []
 
-            with self.assertRaisesRegex(ValueError, "not generated by Farm"):
-                publish(package, True, unmanaged)
+        def unmanaged(method, path, data):
+            calls.append((method, path, data))
+            if path == "":
+                return {"default_branch": "main"}
+            if path.startswith("git/ref/"):
+                return {"object": {"sha": "existing"}}
+            if path.startswith("contents/"):
+                return None
+            return {"sha": "created"}
+
+        with patch.dict("os.environ", {"FARM_RELEASE_TOKEN": "unit-test"}):
+            self.assertTrue(publish(package, True, unmanaged)["published"])
+        tree = next(data for method, path, data in calls
+                    if method == "POST" and path == "git/trees")
+        self.assertNotIn("base_tree", tree)
+        self.assertEqual({entry["path"] for entry in tree["tree"]},
+                         set(read_package(package)))
+        commit = next(data for method, path, data in calls
+                      if method == "POST" and path == "git/commits")
+        self.assertEqual(commit["parents"], ["existing"])
+        self.assertIn(("PATCH", "git/refs/heads/main", {
+            "sha": "created", "force": False,
+        }), calls)
+
+    def test_symlink_and_duplicate_rejected(self):
+        from zipfile import ZipInfo
         for kind in ("duplicate", "link"):
             bad = self.root / (kind + ".zip")
             bad.write_bytes(self.bundle.read_bytes())