fix(proxy): stop prepending SERVER_ROOT_PATH to the UI config path on every restart

The proxy rewrites the packaged UI files in place on each start. For a
SERVER_ROOT_PATH ending in /litellm (e.g. /foo/litellm), the rewritten
config path still contains the original one, so every restart prepended
the root path again (/foo/foo/litellm/.well-known/litellm-ui-config), the
request 404'd and the UI stayed on "Loading...".

Leave already-rewritten paths alone so the rewrite is idempotent.

Fixes #44517

litellm/proxy/proxy_server.py

@@ -2365,6 +2365,20 @@ try:
         except (PermissionError, OSError) as e:
             return False, str(e)
 
+    def _rewrite_ui_config_path(content: str, server_root_path: str) -> str:
+        """
+        Point the UI's config request at server_root_path, keeping already-rewritten paths.
+
+        The UI files are rewritten in place on every startup, and when server_root_path ends
+        in /litellm the rewritten path still contains the original one, so a plain replace
+        would prepend the root path again on each restart.
+        """
+        ui_config_path = f"{server_root_path}/.well-known/litellm-ui-config"
+        return ui_config_path.join(
+            part.replace("/litellm/.well-known/litellm-ui-config", ui_config_path)
+            for part in content.split(ui_config_path)
+        )
+
     # Use a writable runtime UI directory whenever possible.
     # This prevents mutating the packaged UI directory (e.g. site-packages or the repo checkout)
     # and ensures extensionless routes like /ui/login work via <route>/index.html.
@@ -2480,10 +2494,7 @@ try:
                         )
 
                         # Replace the /.well-known/litellm-ui-config with the server root path
-                        modified_content = modified_content.replace(
-                            "/litellm/.well-known/litellm-ui-config",
-                            f"{server_root_path}/.well-known/litellm-ui-config",
-                        )
+                        modified_content = _rewrite_ui_config_path(modified_content, server_root_path)
 
                         with open(file_path, "w", encoding="utf-8") as f:
                             f.write(modified_content)

tests/unit/proxy/proxy_server/test_ui_config_path.py

@@ -0,0 +1,24 @@
+"""SERVER_ROOT_PATH rewrite of the UI's config request (#44517)."""
+
+from __future__ import annotations
+
+import pytest
+
+from litellm.proxy.proxy_server import _rewrite_ui_config_path
+
+# The two shapes the config path takes in the packaged UI bundle
+PACKAGED_UI_CHUNK = (
+    'fetch(`${g}/litellm/.well-known/litellm-ui-config`);const u={url:"/litellm/.well-known/litellm-ui-config"}'
+)
+
+
+@pytest.mark.parametrize("server_root_path", ["/foo", "/litellm", "/foo/litellm"])
+def test_restarts_keep_a_single_root_path_prefix(server_root_path: str) -> None:
+    rewritten = PACKAGED_UI_CHUNK
+    for _ in range(3):  # the proxy rewrites the same UI files on every start
+        rewritten = _rewrite_ui_config_path(rewritten, server_root_path)
+
+    assert rewritten == (
+        f"fetch(`${{g}}{server_root_path}/.well-known/litellm-ui-config`);"
+        f'const u={{url:"{server_root_path}/.well-known/litellm-ui-config"}}'
+    )