Function decide 

pub fn decide(
    rules: &[CompiledRoutingRule],
    source: OperationKey,
) -> RoutingDecision

Decide how to service source on a channel. Routing is driven entirely by stored rules: an explicit rule wins; no matching rule means Unsupported. Channel defaults are materialized into real rules at provider creation (see [crate::api::routing::seed_default_routing]) — they are not recomputed here. A transform_to rule whose dest_kind is missing is malformed and yields Unsupported.