Every meaningful combination of $wgWikiLambdaEnableAbstractClientMode with the three existing mode flags (repo, client, abstract) should either work or be rejected at configuration load time rather than silently half-working at runtime.

The expected production configurations are: (a) abstract.wikipedia.org — repo + abstract, abstract-client off; (b) Wikifunctions — repo only; (c) a local Wikipedia consuming Abstract Content — client + abstract-client, repo and abstract both off; (d) the extension loaded but no modes enabled (dev/test fallback). Combinations that do not match any supported configuration (e.g. abstract on and abstract-client on simultaneously) should produce a clear configuration error at extension load rather than undefined behaviour at first request.