Stale identifier rejection (state.rs):
- WeftShellWindowData gains a closed: AtomicBool field (default false).
- Dispatch<ZweftShellWindowV1, WeftShellWindowData>::request() checks the
closed flag before processing any request; posts a DefunctWindow error
(code 0) if the window has been closed, satisfying the error enum
defined in the protocol XML.
Unit tests (protocols/mod.rs, 5 tests):
- window_data_stores_fields: verifies app_id, title, role, and initial
closed state are stored correctly.
- closed_flag_transition: verifies AtomicBool store/load round-trip.
- manager_interface_name_and_version: confirms generated interface name
zweft_shell_manager_v1 and version 1.
- window_interface_name_and_version: confirms generated interface name
zweft_shell_window_v1 and version 1.
- defunct_window_error_code: confirms Error::DefunctWindow == 0 as
declared in the protocol XML.
Also adds scripts/wsl-test.sh for running cargo test with the
libdisplay-info shim in place.
