Windowed GUI: wm module, input routing, and the paint app

- Add the wm window-manager facility per ADR 0004: overlapping
  pixel-surface windows, damage-rectangle compositing, WM-drawn title
  bar, focus/minimize/close, and F1-F4 keybindings
- Add gop shadow compositing primitives and vt::repaint_region so the
  console stays layer 0 beneath windows
- Route mouse (absolute coords, press/release edges) and keyboard
  (focus-aware input pump) to the focused window
- Add the rspaint drawing-program crate (pen, 8 colors, clear) and shell
  draw/windows/restore commands
- Extend TaskMsg with AppMouse/Focus/Close and document the design in
  CONTEXT.md + ADR 0004

1 files changed, 21 insertions, 4 deletions

diff --git a/rsnix/src/tty.rs b/rsnix/src/tty.rs
index 0783521..6102fb5 100644
--- a/rsnix/src/tty.rs
+++ b/rsnix/src/tty.rs
@@ -41,14 +41,31 @@ static mut RAW_LEN: usize = 0;
 /// Combined blocking key poll: USB HID keyboard first (polled UHCI), then
 /// the PS/2 path (which parks via `hlt` until an IRQ-fed scancode lands).
 fn poll_key() -> KeyEvent {
-    if let Some(ev) = crate::uhci::try_poll_key() {
-        return ev;
+    loop {
+        // A GUI window has focus: the keyboard pump owns the keys.  Park so
+        // the shell/editor don't steal input from the focused app.
+        if crate::wm::focused().is_some() {
+            crate::sched::sleep_ms(5);
+            continue;
+        }
+        if let Some(ev) = crate::uhci::try_poll_key() {
+            return ev;
+        }
+        if let Some(ev) = ps2::try_poll_key() {
+            return ev;
+        }
+        // No key ready: park briefly, then re-check focus (so a focus change
+        // to a GUI window is noticed instead of blocking on a stolen key).
+        crate::sched::sleep_ms(5);
     }
-    ps2::poll_key()
 }
 
-/// Combined non-blocking key poll (USB first, then PS/2).
+/// Combined non-blocking key poll (USB first, then PS/2).  Returns `None`
+/// while a GUI window is focused (the keyboard pump owns the keys).
 fn try_poll_key() -> Option<KeyEvent> {
+    if crate::wm::focused().is_some() {
+        return None;
+    }
     crate::uhci::try_poll_key().or_else(ps2::try_poll_key)
 }