Detached session windows have no close button and cannot be moved (Windows 11)

Version: Claude Code Desktop on Windows 11 Pro 26200, model Opus 5.

Problem

Sessions opened as separate windows (the small per-session windows, not the main window) have a header bar showing only a pin icon and an overflow menu — no close (X) button, and the window cannot be dragged/moved.

The main Claude Code window is unaffected — its title bar has a working X and can be moved normally. All other (non-Claude) Windows applications behave normally.

Reproduction

1. Open several sessions as detached windows
2. Try to close one via its header, or drag it to reposition

Expected: close button present, window draggable.
Actual: no X, window fixed in place. The overflow menu is present but does not resolve it.

Persistence

• Restarting Claude Code: does not help
• Restarting Windows: does not help
• Ctrl+R (reload renderer): no effect
• The state is restored identically after every restart

Measurements taken

Window geometry is healthy — this is not an off-screen or fullscreen condition:

Monitor:  3838 x 1919 (single, primary)
claude:   L=24 T=85 R=1669 B=1693  (1645 x 1608)
          exStyle=0x00280100 -> LAYERED=True, TRANSPARENT=False, TOPMOST=False
          isMaximized=false, isFullScreen=false

%APPDATA%\Claude\window-state.json also shows a normal position (x=32, y=85 on a 3838x1919 display).

Since the geometry is correct while the chrome is missing, the issue appears to be in the rendered window chrome of detached session windows rather than in OS-level window management.

Impact

Detached session windows cannot be closed or rearranged, so a workspace with several concurrent sessions becomes unmanageable.