The initial Slint problem was larger than thought. Hopefully a more universal fix.

docs/testing/background-events.md

@@ -79,3 +79,33 @@ ready to replace the reader.
 
 Preserve a fresh log if lag or a missing announcement remains, with the time
 and the key or update that triggered it. Debug logs can contain private text.
+
+## Window frame geometry
+
+GTK can report the window manager's enclosing frame while X11's active client
+reports only its content area. Slint/i3 exposed this as an active, showing
+1916×994 accessible frame at (0,0) rejected against a 1912×974 client at (2,18).
+Missing or stale `_NET_FRAME_EXTENTS` can make the advertised outer bounds
+identical to those client bounds.
+
+Foreground matching also accepts the actual immediate enclosing X11 frame.
+It must contain the client, have bounded decoration edges, and contain no other
+managed client. The desktop root, a parent that is itself a managed client,
+and shared containers are excluded. Existing process, active/showing state,
+iconification, foreground epoch and same-process sibling checks still apply.
+This covers frame/client discrepancies across applications; arbitrary incorrect
+AT-SPI geometry still requires diagnosis. Rejected activation diagnostics now
+include `x_frame_bounds` alongside client and advertised outer bounds.
+
+```sh
+python3 tests/native_test_session.py env CTHULHU_NATIVE_FRAME_FOREGROUND=1 CTHULHU_NATIVE_GRAB_FOREGROUND=1 go test ./internal/platform/xorg -run '^TestNative(ReparentedFrameForeground|InputOnlyGrabForeground)$' -count=1 -v
+```
+
+The frame fixture covers missing, zero and stale extents, borders, moving,
+resizing, switching to a sibling frame, shared containers and empty workspaces.
+On Slint, listen while switching between two windows from one application,
+another application's window, dialogs and menus. Move and resize them, switch
+away to an empty workspace and return, and check preferences again. Confirm
+speech and Braille follow the foreground control and background activity does
+not take focus. Keep the first rejected activation from a fresh debug log if a
+window remains silent; private X11 results do not prove affected-host acceptance.