fix: serve legacy route aliases during cutover

hub_core/runtime/compat.py

@@ -9,6 +9,7 @@ from uuid import uuid4
 
 import sqlalchemy as sa
 from fastapi import APIRouter, Header, HTTPException, Request, status
+from fastapi.routing import APIRoute
 from fastapi.responses import HTMLResponse, PlainTextResponse, RedirectResponse
 
 from hub_core.runtime.compat_catalogs import (
@@ -504,6 +505,25 @@ def create_compatibility_router() -> APIRouter:
             "<p>Compatibility runtime candidate; projections are authoritative.</p>"
         )
 
+    # Core Hub historically served the same compatibility operations both below
+    # /api/v2 and at the root.  Keep the aliases as real routes (not merely
+    # OpenAPI aliases) so a route-group cutover cannot turn existing clients into
+    # 404s.  The canonical /api/v2 routes remain the only schema-bearing routes;
+    # openapi_json adds the documented alias paths deterministically.
+    for route in list(router.routes):
+        if not isinstance(route, APIRoute) or not route.path.startswith("/api/v2/"):
+            continue
+        alias = route.path.removeprefix("/api/v2")
+        router.add_api_route(
+            alias,
+            route.endpoint,
+            methods=sorted(route.methods or []),
+            status_code=route.status_code,
+            response_class=route.response_class,
+            include_in_schema=False,
+            name=f"legacy_{route.name}",
+        )
+
     return router