Validate incoming request's sitename matches the container's sitename.

This is to mitigate the issue where sometimes request gets routed to wrong worker due to stale caches in the frontend.

No file, test, or entry point is named. Start by tracing incoming request handling and how the worker/container sitename is obtained, then identify where mismatches can be rejected without disrupting valid requests. Done means requests for a different sitename are rejected and matching requests continue normally, with coverage for both cases.

Written by the indexing model from the issue text.