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

2 files changed, 58 insertions, 10 deletions

diff --git a/shell/Cargo.toml b/shell/Cargo.toml
index bc35524..f95b574 100644
--- a/shell/Cargo.toml
+++ b/shell/Cargo.toml
@@ -9,3 +9,4 @@ workspace = true
 [dependencies]
 rsnix = { path = "../rsnix" }
 rsdosedit = { path = "../rsdosedit" }
+rspaint = { path = "../rspaint" }
diff --git a/shell/src/lib.rs b/shell/src/lib.rs
index bb048d8..f1addd9 100644
--- a/shell/src/lib.rs
+++ b/shell/src/lib.rs
@@ -53,14 +53,15 @@ pub fn run() -> ! {
         term_println("!!! PREVIOUS CRASH REPORT:");
         let mut buf = [0u8; 256];
         if let Ok(n) = rsnix::fs::read(h, &mut buf, 0)
-            && n > 0 {
-                let s = core::str::from_utf8(&buf[..n]).unwrap_or("?");
-                for line in s.split('\n') {
-                    if !line.is_empty() {
-                        term_println(line);
-                    }
+            && n > 0
+        {
+            let s = core::str::from_utf8(&buf[..n]).unwrap_or("?");
+            for line in s.split('\n') {
+                if !line.is_empty() {
+                    term_println(line);
                 }
             }
+        }
         term_println("!!! end of crash report");
     }
 
@@ -739,6 +740,9 @@ write `{} <path> TIL <marker>`",
         "touch" => cmd_touch(&parsed),
         "rm" => cmd_rm(&parsed),
         "edit" => cmd_edit(&parsed),
+        "draw" => cmd_draw(&parsed),
+        "windows" => cmd_windows(&parsed),
+        "restore" => cmd_restore(&parsed),
         "bg" => cmd_bg(&parsed),
         "jobs" => cmd_jobs(&parsed),
         "msgrecv" => cmd_msgrecv(&parsed),
@@ -1387,6 +1391,40 @@ fn cmd_edit(p: &Parsed) {
     rsnix::gop::clear_screen();
 }
 
+fn cmd_draw(_p: &Parsed) {
+    match rsnix::sched::spawn(rspaint::run, "paint") {
+        Some(id) => term_println(&alloc::format!(
+            "draw: paint task {} — F4 or the close button to close",
+            id
+        )),
+        None => term_err("draw: task table full"),
+    }
+}
+
+fn cmd_windows(_p: &Parsed) {
+    let list = rsnix::wm::list();
+    if list.is_empty() {
+        term_println("windows: none (console only)");
+        return;
+    }
+    for (id, title, minimized) in list {
+        term_println(&alloc::format!(
+            "  {} {}{}",
+            id,
+            title,
+            if minimized { " (minimized)" } else { "" }
+        ));
+    }
+}
+
+fn cmd_restore(p: &Parsed) {
+    let Some(id) = p.args.first().and_then(|s| s.parse::<usize>().ok()) else {
+        term_err("usage: restore <id>");
+        return;
+    };
+    rsnix::wm::restore(id);
+}
+
 fn cmd_mem(p: &Parsed) {
     let (map, key) = rsnix::memory::get_map();
 
@@ -1602,14 +1640,19 @@ fn cmd_heapdbg(_p: &Parsed) {
         let ov = h.heap_start < fb.saturating_add(fsz) && fb < h.heap_end;
         term_println(&alloc::format!(
             "fb {:#x} size={:#x} overlap-heap={}",
-            fb, fsz, ov
+            fb,
+            fsz,
+            ov
         ));
     }
     let probe = h.heap_start.wrapping_add(0x443e0); // historical crash offset
     match rsnix::memory::freelist_contains(probe) {
         Some((b, s, off)) => term_println(&alloc::format!(
             "probe {:#x} (+0x443e0) IN free blk {:#x} size={:#x} off={:#x}",
-            probe, b, s, off
+            probe,
+            b,
+            s,
+            off
         )),
         None => term_println(&alloc::format!("probe {:#x} (+0x443e0) NOT free", probe)),
     }
@@ -1682,7 +1725,9 @@ fn cmd_heapdbg(_p: &Parsed) {
             let (rc, rr) = rsnix::vt::cell_raw(tr, tc);
             term_println(&alloc::format!(
                 "shadow@{:x} cell={:08x} rendered={:08x}",
-                f, rc, rr
+                f,
+                rc,
+                rr
             ));
         }
     }
@@ -1697,7 +1742,9 @@ fn cmd_heapdbg(_p: &Parsed) {
             match rsnix::memory::freelist_contains(b) {
                 Some((fb, fs, fo)) => term_println(&alloc::format!(
                     "shadow base IN free list: blk {:#x} size={:#x} off={:#x}",
-                    fb, fs, fo
+                    fb,
+                    fs,
+                    fo
                 )),
                 None => term_println("shadow base NOT in free list"),
             }