Send keys to windows whose focus isn't a text field #13

Found in the Ace desktop tools study (githubnext/ace#427), scenario D2 on Canary 0.0.46+dd15840.

Observed: desktop_key Escape to a Finder window, with a file row selected, was refused twice: "The snapshot has no exact focused control. Click a control, then inspect the window again." The agent clicked a row and tried again, and it was refused again.

Cause: native/sources/client/actions.swift refuses key and insert when the snapshot has no focusedElement. Peekaboo's background input driver only resolves a focused text element as the receiver (focusedTextElement in BackgroundInputDriver.swift). So keys only work while a text field has focus. Escape, arrow keys, Return, Space (Quick Look) and Cmd shortcuts in lists, outlines, canvases and the Finder can't be sent. The hint suggests a click that can't help.

Options:

• Admit a non-text focused receiver (a list, outline, table or web area) with the same exact process, window and focus checks, using background delivery when the app accepts it.
• Or expose foreground key delivery for an exact window that has been activated, with the outcome left unknown when focus can't be read back. This is the --foreground gap from [Meta] Complete native computer use in Ace #11.

Short term, the refusal should say that keys need a focused text field, and point to desktop_menu when the command is in a menu.