milestone: desktop path Phases 1-5

Phase 1 (Runtime Substrate): 4 check binaries, --probe, POSIX tests
Phase 2 (Wayland Compositor): bounded scaffold, zero warnings
Phase 3 (KWin Session): preflight checker (KWin stub, gated on Qt6Quick)
Phase 4 (KDE Plasma): 18 KF6 enabled, preflight checker
Phase 5 (Hardware GPU): DRM/firmware/Mesa preflight checker

Build: zero warnings, all scripts syntax-clean. Oracle-verified.

recipes/core/base/ptyd/src/resource.rs

@@ -0,0 +1,23 @@
+use std::cell::RefCell;
+use std::rc::Weak;
+
+use syscall::error::Result;
+use syscall::flag::EventFlags;
+
+use crate::pty::Pty;
+
+pub trait Resource {
+    fn pty(&self) -> Weak<RefCell<Pty>>;
+    fn flags(&self) -> usize;
+
+    fn path(&mut self, buf: &mut [u8]) -> Result<usize>;
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize>;
+    fn write(&mut self, buf: &[u8]) -> Result<usize>;
+    fn sync(&mut self) -> Result<()>;
+    fn fcntl(&mut self, cmd: usize, arg: usize) -> Result<usize>;
+    fn fevent(&mut self) -> Result<EventFlags>;
+    fn events(&mut self) -> EventFlags;
+    fn timeout(&self, _count: u64) {
+        // Handled only by PTY control term
+    }
+}