[AThraen]

Problem

Sometimes typing in a pane makes the letters appear in a different pane. MainViewModel.ActiveSession drives the highlight, but keystrokes follow Win32 keyboard focus. Two paths let the two drift apart:

1. Clicking a pane while CSM is in the background. OnWindowActivated BeginInvoked FocusTerminal() on the previous active session. Meanwhile the page's capture-phase mousedown posts activate, a cross-process message, which promotes the clicked pane. Whichever lands last wins. When the stale refocus won, the highlight moved to the clicked pane and the keystrokes kept going to the old one.
2. Restart. The teardown hands ActiveSession to Sessions.LastOrDefault(). The wasActive restore then set ActiveSession back to the revived session but never focused it.

Fix

• OnWindowActivated skips the refocus while any mouse button is down (GetAsyncKeyState, all three buttons, because swapped mouse buttons are physical). A click-to-activate is the user choosing the target. Alt+Tab and taskbar activation still refocus the active terminal as before.
• PaneActivated (a click in a pane) now promotes and focuses that pane. This makes the result independent of the order in which the activation and the page message arrive. It is throttled to 300 ms on the page side.
• The restart wasActive path calls FocusTerminal() on the revived session.
• CLAUDE.md "What makes a session active" records the rule: setting ActiveSession moves the highlight, not the keyboard.

Testing

• dotnet build passes and the unit tests pass (1183/1183).
• Not covered by automated tests: the race needs a real focus change between processes and WebView2, which the headless suite can't drive. Manual checks:
  • With CSM in the background and pane A active, click directly into pane B and type. Text goes to B.
  • Alt+Tab back into CSM and type. Text goes to the highlighted pane.
  • Restart (↻) the active session, wait for it to come back, and type. Text goes to it.

🤖 Generated with Claude Code