Fix 'Edit In Place' feature appending instead of editing messages

[bzqzheng]

Summary

• Fixes issue "Edit In Place" feature only appends instead of edits #6954 where "Edit In Place" feature appends the edited content as a new message instead of replacing the existing message
• Modifies the onMessageUpdate function to properly update the content of the edited message instead of creating a new one
• Preserves existing image content if present in the message being edited

Test plan

1. Open an existing conversation with multiple messages
2. Hover over a user message and click the "Edit" button
3. Modify the message content
4. Click "Edit in Place"
5. Verify that the edited content replaces the original message and doesn't appear as a new message
6. Verify that messages after the edited message are removed as expected

🤖 Generated with Claude Code

[katzdave]

Can you try reloading a session from history; does it follow the expectation there where the old message is removed/replaced?

[Copilot]

Pull request overview

This PR fixes issue #6954 where the "Edit In Place" feature was appending edited messages as new messages instead of replacing the existing message content.

Changes:

• Modified onMessageUpdate function to properly update the last user message in place after truncating the session
• Added logic to preserve existing image content when editing a message
• Implemented proper message content replacement before requesting a new assistant response

[bzqzheng]

Can you try reloading a session from history; does it follow the expectation there where the old message is removed/replaced?

not sure if i understand this question.

I'm experiencing the same issue from reloading the past sessions;

[zanesq]

@bzqzheng thanks cleaned it up and added a working state, tested locally I think this is gtg!

@katzdave yes it does on refresh, verified locally