fix(delegate-task): preserve model variant in metadata resolution

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/resolve-metadata-model.ts

@@ -3,19 +3,37 @@ import type { DelegatedModelConfig } from "./types"
 export interface MetadataModel {
   providerID: string
   modelID: string
+  variant?: string
 }
 
-type ModelLike = Pick<DelegatedModelConfig, "providerID" | "modelID"> | MetadataModel
+type ModelLike = Pick<DelegatedModelConfig, "providerID" | "modelID" | "variant"> | MetadataModel
+
+function isModelLike(value: unknown): value is ModelLike {
+  return typeof value === "object"
+    && value !== null
+    && "providerID" in value
+    && typeof value.providerID === "string"
+    && "modelID" in value
+    && typeof value.modelID === "string"
+}
+
+function toMetadataModel(model: ModelLike): MetadataModel {
+  return {
+    providerID: model.providerID,
+    modelID: model.modelID,
+    ...("variant" in model && model.variant ? { variant: model.variant } : {}),
+  }
+}
 
 export function resolveMetadataModel(
   primary: ModelLike | undefined,
   fallback: ModelLike | undefined,
 ): MetadataModel | undefined {
-  if (primary) {
-    return { providerID: primary.providerID, modelID: primary.modelID }
+  if (isModelLike(primary)) {
+    return toMetadataModel(primary)
   }
-  if (fallback) {
-    return { providerID: fallback.providerID, modelID: fallback.modelID }
+  if (isModelLike(fallback)) {
+    return toMetadataModel(fallback)
   }
   return undefined
 }