Class FallbackRouter

control_layer.py:659–691

When the primary strategy exhausts all retries, routes to a registered fallback handler. Fallbacks are called in registration order. First non-empty response wins.

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class FallbackRouter:
    """
    When the primary strategy exhausts all retries, routes to a
    registered fallback handler.

    Fallbacks are called in registration order. First non-empty response wins.
    """

    def __init__(self):
        self._strategies: Dict[str, Callable[[str], str]] = {}
        self._order: List[str] = []

    def register(self, name: str, fn: Callable[[str], str]) -> None:
        self._strategies[name] = fn
        if name not in self._order:
            self._order.append(name)

    def route(
        self, user_input: str, failure_mode: FailureMode
    ) -> Tuple[str, str]:
        for name in self._order:
            try:
                response = self._strategies[name](user_input)
                if response:
                    log.info(
                        "fallback.used",
                        strategy=name,
                        failure_mode=failure_mode.value,
                    )
                    return name, response
            except Exception as exc:
                log.error("fallback.error", strategy=name, error=str(exc))
        return "none", ""


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