diff --git a/passkey/fastapi/mainapp.py b/passkey/fastapi/mainapp.py
index 9a6945e..fc5d23e 100644
--- a/passkey/fastapi/mainapp.py
+++ b/passkey/fastapi/mainapp.py
@@ -42,6 +42,16 @@ async def lifespan(app: FastAPI):  # pragma: no cover - startup path
         logging.error(f"⚠️ {e}")
         # Re-raise to fail fast
         raise
+
+    # In dev mode, Vite serves assets directly; in production, mount static files
+    # This is deferred to lifespan because PASSKEY_DEVMODE is set after module import
+    if not frontend.is_dev_mode():
+        app.mount(
+            "/auth/assets/",
+            StaticFiles(directory=frontend.file("auth", "assets")),
+            name="assets",
+        )
+
     yield
     # (Optional) add shutdown cleanup here later
 
@@ -54,11 +64,6 @@ app.middleware("http")(auth_host.redirect_middleware)
 app.mount("/auth/api/admin/", admin.app)
 app.mount("/auth/api/", api.app)
 app.mount("/auth/ws/", ws.app)
-app.mount(
-    "/auth/assets/",
-    StaticFiles(directory=frontend.file("auth", "assets")),
-    name="assets",
-)
 
 
 @app.get("/auth/restricted/")
diff --git a/passkey/util/frontend.py b/passkey/util/frontend.py
index 02f9f00..2dbe129 100644
--- a/passkey/util/frontend.py
+++ b/passkey/util/frontend.py
@@ -12,7 +12,7 @@ from threading import Thread
 
 import httpx
 
-__all__ = ["path", "file", "read", "run_dev"]
+__all__ = ["path", "file", "read", "run_dev", "is_dev_mode"]
 
 DEV_SERVER = "http://localhost:4403"
 
@@ -60,7 +60,7 @@ def file(*parts: str) -> Path:
     return path.joinpath(*parts)
 
 
-def _is_dev_mode() -> bool:
+def is_dev_mode() -> bool:
     """Check if we're running in dev mode (Vite frontend server)."""
     return os.environ.get("PASSKEY_DEVMODE") == "1"
 
@@ -78,7 +78,7 @@ async def read(filepath: str) -> tuple[bytes, int, dict[str, str]]:
         Tuple of (content, status_code, headers) suitable for
         FastAPI Response(*args) or Sanic raw response.
     """
-    if _is_dev_mode():
+    if is_dev_mode():
         async with httpx.AsyncClient() as client:
             resp = await client.get(f"{DEV_SERVER}{filepath}")
             resp.raise_for_status()