Introduce APIGone exception for removed APIs

Introduce a new exception class APIGone to indicate that certain API
features have been removed and are no longer available. Update the
security integrity check endpoint to raise this new exception instead
of a generic APIError, providing clearer communication to clients that
the feature has been intentionally removed.

Author: agners

supervisor/api/security.py

@@ -5,6 +5,8 @@
 from aiohttp import web
 import voluptuous as vol
 
+from supervisor.exceptions import APIGone
+
 from ..const import ATTR_CONTENT_TRUST, ATTR_FORCE_SECURITY, ATTR_PWNED
 from ..coresys import CoreSysAttributes
 from .utils import api_process, api_validate
@@ -52,6 +54,6 @@ async def integrity_check(self, request: web.Request) -> dict[str, Any]:
         """Run backend integrity check.
 
         CodeNotary integrity checking has been removed. This endpoint now returns
-        an error indicating the feature is currently non-functional.
+        an error indicating the feature is gone.
         """
-        return {"error": "No integrity checking available"}
+        raise APIGone("Integrity check feature has been removed.")

supervisor/exceptions.py

@@ -423,6 +423,12 @@ class APINotFound(APIError):
     status = 404
 
 
+class APIGone(APIError):
+    """API is no longer available."""
+
+    status = 410
+
+
 class APIAddonNotInstalled(APIError):
     """Not installed addon requested at addons API."""