Bypass mount redirect for /admin with relative redirect

app/main.py

@@ -15,6 +15,8 @@ from typing import AsyncGenerator
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
+from starlette.responses import RedirectResponse
+from starlette.status import HTTP_303_SEE_OTHER
 
 from app.core.config import get_settings
 from app.database import close_db, init_db
@@ -177,6 +179,12 @@ app.include_router(
 if settings.ENABLE_ADMIN:
     from app.admin import admin as admin_app
 
+    @app.get("/admin", include_in_schema=False)
+    async def admin_entrypoint():
+        # Avoid Starlette mount slash-normalization redirect, which can emit an
+        # absolute URL based on proxy headers such as https://127.0.0.1/admin/.
+        return RedirectResponse(url="/admin/", status_code=HTTP_303_SEE_OTHER)
+
     app.include_router(
         ai_router,
         prefix=f"{settings.API_V1_STR}",