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.

No files or tests are named. Start by tracing active task execution through temporary rate-limit errors and identify the existing retry and user-notification paths; done means temporary limits retry with the same model and effort, retries are bounded and spaced, and unrecoverable tasks stop with a clear notice.

索引モデルが issue の本文から書いたものです。