Fix model fallback across main/background/sync agents

src/features/task-toast-manager/manager.test.ts

@@ -217,6 +217,27 @@ describe("TaskToastManager", () => {
       expect(call.body.message).toContain("(inherited from parent)")
     })
 
+    test("should display warning when model is runtime fallback", () => {
+      // given - runtime-fallback indicates a model swap mid-run
+      const task = {
+        id: "task_runtime",
+        description: "Task with runtime fallback model",
+        agent: "explore",
+        isBackground: false,
+        modelInfo: { model: "quotio/oswe-vscode-prime", type: "runtime-fallback" as const },
+      }
+
+      // when - addTask is called
+      toastManager.addTask(task)
+
+      // then - toast should show fallback warning
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).toContain("[FALLBACK]")
+      expect(call.body.message).toContain("quotio/oswe-vscode-prime")
+      expect(call.body.message).toContain("(runtime fallback)")
+    })
+
     test("should not display model info when user-defined", () => {
       // given - a task with user-defined model
       const task = {
@@ -257,4 +278,32 @@ describe("TaskToastManager", () => {
       expect(call.body.message).not.toContain("[FALLBACK] Model:")
     })
   })
+
+  describe("updateTaskModelBySession", () => {
+    test("updates task model info and shows fallback toast", () => {
+      // given - task without model info
+      const task = {
+        id: "task_update",
+        sessionID: "ses_update_1",
+        description: "Task that will fallback",
+        agent: "explore",
+        isBackground: false,
+      }
+      toastManager.addTask(task)
+      mockClient.tui.showToast.mockClear()
+
+      // when - runtime fallback applied by session
+      toastManager.updateTaskModelBySession("ses_update_1", {
+        model: "nvidia/stepfun-ai/step-3.5-flash",
+        type: "runtime-fallback",
+      })
+
+      // then - new toast shows fallback model
+      expect(mockClient.tui.showToast).toHaveBeenCalled()
+      const call = mockClient.tui.showToast.mock.calls[0][0]
+      expect(call.body.message).toContain("[FALLBACK]")
+      expect(call.body.message).toContain("nvidia/stepfun-ai/step-3.5-flash")
+      expect(call.body.message).toContain("(runtime fallback)")
+    })
+  })
 })

src/features/task-toast-manager/manager.ts

@@ -20,6 +20,7 @@ export class TaskToastManager {
 
   addTask(task: {
     id: string
+    sessionID?: string
     description: string
     agent: string
     isBackground: boolean
@@ -30,6 +31,7 @@ export class TaskToastManager {
   }): void {
     const trackedTask: TrackedTask = {
       id: task.id,
+      sessionID: task.sessionID,
       description: task.description,
       agent: task.agent,
       status: task.status ?? "running",
@@ -54,6 +56,18 @@ export class TaskToastManager {
     }
   }
 
+  /**
+   * Update model info for a task by session ID
+   */
+  updateTaskModelBySession(sessionID: string, modelInfo: ModelFallbackInfo): void {
+    if (!sessionID) return
+    const task = Array.from(this.tasks.values()).find((t) => t.sessionID === sessionID)
+    if (!task) return
+    if (task.modelInfo?.model === modelInfo.model && task.modelInfo?.type === modelInfo.type) return
+    task.modelInfo = modelInfo
+    this.showTaskListToast(task)
+  }
+
   /**
    * Remove completed/error task
    */
@@ -110,14 +124,17 @@ export class TaskToastManager {
     const lines: string[] = []
 
     const isFallback = newTask.modelInfo && (
-      newTask.modelInfo.type === "inherited" || newTask.modelInfo.type === "system-default"
+      newTask.modelInfo.type === "inherited" ||
+      newTask.modelInfo.type === "system-default" ||
+      newTask.modelInfo.type === "runtime-fallback"
     )
     if (isFallback) {
-      const suffixMap: Record<"inherited" | "system-default", string> = {
+      const suffixMap: Record<"inherited" | "system-default" | "runtime-fallback", string> = {
         inherited: " (inherited from parent)",
         "system-default": " (system default fallback)",
+        "runtime-fallback": " (runtime fallback)",
       }
-      const suffix = suffixMap[newTask.modelInfo!.type as "inherited" | "system-default"]
+      const suffix = suffixMap[newTask.modelInfo!.type as "inherited" | "system-default" | "runtime-fallback"]
       lines.push(`[FALLBACK] Model: ${newTask.modelInfo!.model}${suffix}`)
       lines.push("")
     }

src/features/task-toast-manager/types.ts

@@ -4,12 +4,13 @@ export type TaskStatus = "running" | "queued" | "completed" | "error"
 
 export interface ModelFallbackInfo {
   model: string
-  type: "user-defined" | "inherited" | "category-default" | "system-default"
+  type: "user-defined" | "inherited" | "category-default" | "system-default" | "runtime-fallback"
   source?: ModelSource
 }
 
 export interface TrackedTask {
   id: string
+  sessionID?: string
   description: string
   agent: string
   status: TaskStatus