[FEATURE]: ACP: Send diff on `apply_patch`

[imnotlxy]

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

See: https://agentclientprotocol.com/protocol/v1/tool-calls#diffs

When an agent edits a file (using apply_patch), the diff should be sent to the client through ACP. In this way, users can see what the agent is editing in clients like Zed.

[github-actions]

This issue doesn't fully meet our contributing guidelines.

What needs to be fixed:

• The Describe the enhancement you want to request field lacks sufficient detail. It only contains an external link and a screenshot, but no explanation of what the enhancement should do, why it is needed, or what problem it solves. Please describe the desired behavior in your own words.

Please edit this issue to address the above within 2 hours, or it will be automatically closed.

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[github-actions]

Thanks for updating the issue! It now meets our contributing guidelines. We appreciate the clear description and the reference to the ACP protocol spec.