Temporary rate limits stop active task execution instead of retrying

### Description

Copilot App sometimes stops an active task after displaying a temporary rate-limit error:

> You’ve hit your rate limit. Please wait for your limit to reset in under a minute or switch to auto model to continue.

### Steps to reproduce

1. Start a longer-running task using Sol with Extra High effort.
2. If a temporary rate limit occurs, observe the session behavior.

### Expected behavior

When the rate limit is temporary, Copilot App should wait and retry the task using the same model and effort level rather than stopping execution.

The retry behavior should be considerate of upstream providers, allowing sufficient time between attempts and limiting retries so that recovery attempts do not add unnecessary load.

If the task cannot be resumed after a reasonable period, the app should stop and clearly notify the user.

### Actual behavior

Execution stops after the rate-limit error and does not automatically resume, despite the message stating that the limit should reset in under a minute.

### Impact

Long-running or delegated tasks can terminate because of a short-lived rate limit. The user must notice the interruption and manually continue or restart the task.

未指定文件或测试。首先跟踪活动任务在遇到临时速率限制错误时的执行流程，并识别现有的重试和用户通知路径；完成的标准是：临时限制使用相同的模型和工作量进行重试，重试次数受到限制且间隔进行，并且无法恢复的任务会在发出明确通知后停止。

由索引模型根据 Issue 内容生成。