rsnix v0.4.0: GUI input foundation — PS/2 mouse + scheduler message queues

Mouse (IRQ12, stream mode): ByteRing generalized for both PS/2 devices,
ISR routes data-port bytes by the controller's aux bit; mouse_init with
bounded-ACK handshake (boots without a mouse); packet decoder with
bit-3 resync, screen-relative deltas, buttons.  Exposed as /dev/mouse,
the `mouse` stream command, and `make test-mouse`.

Message queues (ADR 0003's GUI-era primitive): every task gets a static
16-slot TaskMsg ring; send/recv/recv_blocking with direct wake + tick
scan safety net for the lost-wakeup race; `msgrecv`/`send` commands,
`mouse <id>` routes real IRQ12 events into a task's queue, jobs shows
q=.  `make test-msg` + `make test-disk` regression pass.

1 files changed, 38 insertions, 0 deletions

diff --git a/rsnix/src/fs.rs b/rsnix/src/fs.rs
index b560bfa..0b7a772 100644
--- a/rsnix/src/fs.rs
+++ b/rsnix/src/fs.rs
@@ -46,6 +46,7 @@ enum CharDevice {
     Zero,
     Console,
     Serial,
+    Mouse,
 }
 
 enum NodeData {
@@ -171,6 +172,12 @@ pub fn init() -> (usize, usize) {
         FileType::Char,
         NodeData::Char(CharDevice::Serial),
     );
+    add(
+        "mouse",
+        Some(dev),
+        FileType::Char,
+        NodeData::Char(CharDevice::Mouse),
+    );
 
     add(
         "motd",
@@ -700,11 +707,42 @@ fn dev_text(dev: CharDevice, _pos: u64) -> String {
         CharDevice::Version => version_text(),
         CharDevice::Meminfo => meminfo_text(),
         CharDevice::Klog => crate::klog::dump(),
+        CharDevice::Mouse => mouse_text(),
         CharDevice::Null | CharDevice::Console | CharDevice::Serial => String::new(),
         CharDevice::Zero => String::new(),
     }
 }
 
+/// Render `/dev/mouse`: drain every pending PS/2 event (up to 32) into one
+/// line each, so `cat /dev/mouse` shows the movement that happened since
+/// the last read.  Falls back to a clear message when there is no device or
+/// nothing pending.
+fn mouse_text() -> String {
+    if !crate::ps2::mouse_present() {
+        return String::from("mouse: no PS/2 mouse\n");
+    }
+    let mut s = String::new();
+    for _ in 0..32 {
+        let Some(ev) = crate::ps2::try_poll_mouse() else {
+            break;
+        };
+        let mut b = String::new();
+        b.push(if ev.left { 'L' } else { '-' });
+        b.push(if ev.right { 'R' } else { '-' });
+        b.push(if ev.middle { 'M' } else { '-' });
+        s.push_str(&alloc::format!(
+            "dx={:+} dy={:+} buttons={}\n",
+            ev.dx,
+            ev.dy,
+            b
+        ));
+    }
+    if s.is_empty() {
+        s.push_str("mouse: no events\n");
+    }
+    s
+}
+
 // --- self-test ------------------------------------------------------------
 
 pub fn self_test() -> bool {