feat(sisyphus-task): inherit parent model for categories and show fallback warning

- Change model priority: user override > parent model > category default
- Add ModelFallbackInfo to track model resolution type
- Show warning toast when category uses inherited or default model
- Add tests for model fallback info in task toast

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

@@ -1,5 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin"
-import type { TrackedTask, TaskStatus } from "./types"
+import type { TrackedTask, TaskStatus, ModelFallbackInfo } from "./types"
 import type { ConcurrencyManager } from "../background-agent/concurrency"
 
 type OpencodeClient = PluginInput["client"]
@@ -25,6 +25,7 @@ export class TaskToastManager {
     isBackground: boolean
     status?: TaskStatus
     skills?: string[]
+    modelInfo?: ModelFallbackInfo
   }): void {
     const trackedTask: TrackedTask = {
       id: task.id,
@@ -34,6 +35,7 @@ export class TaskToastManager {
       startedAt: new Date(),
       isBackground: task.isBackground,
       skills: task.skills,
+      modelInfo: task.modelInfo,
     }
 
     this.tasks.set(task.id, trackedTask)
@@ -105,6 +107,14 @@ export class TaskToastManager {
 
     const lines: string[] = []
 
+    // Show model fallback warning for the new task if applicable
+    if (newTask.modelInfo && newTask.modelInfo.type !== "user-defined") {
+      const icon = "⚠️"
+      const suffix = newTask.modelInfo.type === "inherited" ? " (inherited)" : " (default)"
+      lines.push(`${icon} Model: ${newTask.modelInfo.model}${suffix}`)
+      lines.push("")
+    }
+
     if (running.length > 0) {
       lines.push(`Running (${running.length}):${concurrencyInfo}`)
       for (const task of running) {