fix: enable runtime fallback for delegated child sessions (#2357)

src/hooks/runtime-fallback/retry-model-payload.ts

@@ -0,0 +1,25 @@
+import { parseModelString } from "../../tools/delegate-task/model-string-parser"
+
+export function buildRetryModelPayload(
+  model: string,
+): { model: { providerID: string; modelID: string }; variant?: string } | undefined {
+  const parsedModel = parseModelString(model)
+  if (!parsedModel) {
+    return undefined
+  }
+
+  return parsedModel.variant
+    ? {
+        model: {
+          providerID: parsedModel.providerID,
+          modelID: parsedModel.modelID,
+        },
+        variant: parsedModel.variant,
+      }
+    : {
+        model: {
+          providerID: parsedModel.providerID,
+          modelID: parsedModel.modelID,
+        },
+      }
+}