Desktop app: message input box refills with previously sent message after every send

## Description
After sending a message in the Claude Code Desktop app chat, the text input box does not clear. Instead, it repopulates with the message that was just sent, forcing the user to manually select and delete the text before typing the next message.

## Steps to reproduce
1. Open the Claude Code Desktop app (chat/Code tab).
2. Type a message in the chat input field.
3. Send the message.
4. Observe the input field: the just-sent message text reappears in it.

## Expected behavior
The input box should be empty after a message is sent.

## Actual behavior
The input box is repopulated with the previous message every single time a message is sent, requiring manual deletion before entering the next message.

## Frequency
Happens consistently, on every sent message (not intermittent).

## When it started
The user reports this began after a recent app update.

## Environment
- App: Claude Code Desktop app
- OS: Windows 11 IoT Enterprise 10.0.26200
- Exact app version: not confirmed at time of filing — happy to provide if requested

## Impact
Minor but persistent workflow disruption: requires manually selecting and deleting leftover text before every new message.

Start by reproducing the issue in the Claude Code Desktop app's chat/Code tab on Windows, then trace the message-send handling and input state. Done means the input box is empty after every sent message and remains ready for the next message.

Written by the indexing model from the issue text.