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, 25 insertions, 0 deletions

diff --git a/rsnix/src/vt.rs b/rsnix/src/vt.rs
index 9444063..c5fc5fd 100644
--- a/rsnix/src/vt.rs
+++ b/rsnix/src/vt.rs
@@ -147,6 +147,31 @@ pub fn size() -> (usize, usize) {
     unsafe { (ROWS, COLS) }
 }
 
+/// Re-render the console's cells into the shadow for a pixel region, so the
+/// window manager can restore the console (layer 0) beneath a window that
+/// moved, closed, or was minimized.  Does not push — the caller pushes once.
+pub fn repaint_region(x: usize, y: usize, w: usize, h: usize) {
+    unsafe {
+        if CELLS.is_null() {
+            return;
+        }
+        let (cols, rows) = (COLS, ROWS);
+        let c0 = x / 8;
+        let c1 = (x + w).div_ceil(8).min(cols);
+        let r0 = y / 16;
+        let r1 = (y + h).div_ceil(16).min(rows);
+        let cells = &*CELLS;
+        for r in r0..r1 {
+            for c in c0..c1 {
+                let cell = cells[r * cols + c];
+                let fg = PALETTE[cell.fg as usize];
+                let bg = PALETTE[cell.bg as usize];
+                crate::gop::shadow_glyph_px(c * 8, r * 16, cell.ch, fg, bg);
+            }
+        }
+    }
+}
+
 /// DEBUG (crash-family): read one cell's raw word (ch | fg<<16 | bg<<24)
 /// from the live cells grid and the rendered grid, for the given text
 /// row/col.  Returns (raw_cell, raw_rendered).