fix(background): use parent session variant in notifyParentSession instead of child task variant

src/features/background-agent/manager.ts

@@ -1783,6 +1783,7 @@ export class BackgroundManager {
       let agent: string | undefined = task.parentAgent
       let model: { providerID: string; modelID: string } | undefined
       let tools: Record<string, boolean> | undefined = task.parentTools
+      let promptContext: ReturnType<typeof resolvePromptContextFromSessionMessages> = null
 
       if (this.enableParentSessionNotifications) {
         try {
@@ -1796,7 +1797,7 @@ export class BackgroundManager {
               tools?: Record<string, boolean | "allow" | "deny" | "ask">
             }
           }>)
-          const promptContext = resolvePromptContextFromSessionMessages(
+          promptContext = resolvePromptContextFromSessionMessages(
             messages,
             task.parentSessionID,
           )
@@ -1840,7 +1841,7 @@ export class BackgroundManager {
         const isTaskFailure = task.status === "error" || task.status === "cancelled" || task.status === "interrupt"
         const shouldReply = allComplete || isTaskFailure
 
-        const variant = task.model?.variant
+        const variant = promptContext?.model?.variant
 
         try {
           await this.client.session.promptAsync({