Persist hidden chat state when reopening a session in an editor window

When opening an editor window from a session in the Agents window, the session chat is shown automatically. If the user hides that chat and later opens the same session (or navigates to another session) in an editor window, the chat is shown again.

The editor window should respect the user's choice to hide the session chat instead of reopening it on subsequent launches from the Agents window.

## Steps to reproduce

1. Open a session from the Agents window in an editor window.
2. Hide the session chat in the editor window.
3. Return to the Agents window and open a session in an editor window again.

## Expected

The chat remains hidden, preserving the user's editor window state.

## Actual

The chat is shown again each time a session is opened in an editor window.

_Created from a [Slack conversation](https://vscodeteam.slack.com/archives/C09MVCZKLP4/p1788433077967879?thread_ts=1788433077.967879&cid=C09MVCZKLP4)._