[FEATURE]: Prompt spinner should stay tied to the running agent

[Lolfaceftw]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

I want the bottom-left prompt spinner to stay tied to the agent that's actually running.

Right now, if a run starts with Build and I switch the selected agent to Plan before the response finishes, the spinner changes to Plan's color even though Build is still doing the work.

Requested behavior: keep the spinner on the running agent's color until the run finishes, so the loading indicator reflects the active agent instead of the current selection.

[github-actions]

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What needs to be fixed:

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[github-actions]

Thanks for updating the issue! The description clearly explains the current behavior, the expected behavior, and how to reproduce it. Everything looks good now.