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

src/features/background-agent/manager.test.ts

@@ -1059,7 +1059,18 @@ describe("BackgroundManager.notifyParentSession - aborted parent", () => {
         prompt: promptMock,
         promptAsync: promptMock,
         abort: async () => ({}),
-        messages: async () => ({ data: [] }),
+        messages: async () => ({
+          data: [{
+            info: {
+              agent: "explore",
+              model: {
+                providerID: "anthropic",
+                modelID: "claude-opus-4-6",
+                variant: "high",
+              },
+            },
+          }],
+        }),
       },
     }
     const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput)
@@ -1219,6 +1230,58 @@ describe("BackgroundManager.notifyParentSession - variant propagation", () => {
     manager.shutdown()
   })
 
+  test("should prefer parent session variant over child task variant in parent notification promptAsync body", async () => {
+    //#given
+    const promptCalls: Array<{ body: Record<string, unknown> }> = []
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        promptAsync: async (args: { path: { id: string }; body: Record<string, unknown> }) => {
+          promptCalls.push({ body: args.body })
+          return {}
+        },
+        abort: async () => ({}),
+        messages: async () => ({
+          data: [{
+            info: {
+              agent: "explore",
+              model: {
+                providerID: "anthropic",
+                modelID: "claude-opus-4-6",
+                variant: "max",
+              },
+            },
+          }],
+        }),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput)
+    const task: BackgroundTask = {
+      id: "task-parent-variant-wins",
+      sessionID: "session-child",
+      parentSessionID: "session-parent",
+      parentMessageID: "msg-parent",
+      description: "task with mismatched variant",
+      prompt: "test",
+      agent: "explore",
+      status: "completed",
+      startedAt: new Date(),
+      completedAt: new Date(),
+      model: { providerID: "anthropic", modelID: "claude-opus-4-6", variant: "high" },
+    }
+    getPendingByParent(manager).set("session-parent", new Set([task.id]))
+
+    //#when
+    await (manager as unknown as { notifyParentSession: (task: BackgroundTask) => Promise<void> })
+      .notifyParentSession(task)
+
+    //#then
+    expect(promptCalls).toHaveLength(1)
+    expect(promptCalls[0].body.variant).toBe("max")
+
+    manager.shutdown()
+  })
+
   test("should not include variant in promptAsync body when task has no variant", async () => {
     //#given
     const promptCalls: Array<{ body: Record<string, unknown> }> = []

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({