defaultReasoningEffortFor function
SwiftInferReasoningEffort.medium for a qwen3.8 node, else null — an
unset effort is omitted from the body, leaving the node's card default.
Implementation
SwiftInferReasoningEffort? defaultReasoningEffortFor(String modelId) =>
modelId.startsWith(kQwen38IdPrefix)
? SwiftInferReasoningEffort.medium
: null;