Follow-up to the reply-language feature. `_model_or_none` was private to
LlmBuilderAgent, so the advance-task wiring reached it via a fragile
`getattr(agent, "_model_or_none", lambda: None)`. Make it part of the
DifyBuilderAgent protocol (typed `object | None` to keep the pure port free of
any model-runtime import) and implement it on every conforming agent
(LlmBuilderAgent renames the private method public; PlaceholderAgent and the
test doubles return None). The Localizer wiring now uses `agent.model_or_none`
directly. Also drops the useless-return ruff nit in the wiring test.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Charles YaoandClaude Opus 4.8
9b4e095e71