refactor: extract ports/drivers/bins layers — clean dependency inversion

Separate abstractions from implementations following DIP:

  servers/              drivers/
      │                     │
      ▼                     ▼
    ports/  (trait-only crates, zero deps)

New crates:

ports/ (abstractions):
  - port-framebuffer: Framebuffer trait
  - port-block-device: BlockDevice trait + SectorId
  - port-input-device: InputDevice trait + InputEvent types

drivers/ (implementations depend on ports/):
  - driver-framebuffer-virtio: VirtIO GPU framebuffer
  - driver-framebuffer-mock: test double
  - driver-block-virtio: VirtIO block device

bins/ (composition roots wire server + driver):
  - display-qemu: DisplayServer<VirtioFramebuffer>
  - storage-qemu: storage server with VirtIO block

Servers no longer own their hardware traits or driver code.
Neither server nor driver depends on the other — both point
inward to the port abstraction.

crates/ports/block-device/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "port-block-device"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

crates/ports/block-device/src/lib.rs

@@ -0,0 +1,21 @@
+#![no_std]
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SectorId(u32);
+
+impl SectorId {
+    pub const fn new(id: u32) -> Self {
+        Self(id)
+    }
+
+    pub const fn raw(&self) -> u32 {
+        self.0
+    }
+}
+
+pub trait BlockDevice {
+    fn sector_size(&self) -> usize;
+    fn sector_count(&self) -> usize;
+    fn read_sector(&mut self, sector: SectorId, buf: &mut [u8]) -> bool;
+    fn write_sector(&mut self, sector: SectorId, buf: &[u8]) -> bool;
+}

crates/ports/framebuffer/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "port-framebuffer"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

crates/ports/framebuffer/src/lib.rs

@@ -0,0 +1,10 @@
+#![no_std]
+
+pub trait Framebuffer {
+    fn width(&self) -> u16;
+    fn height(&self) -> u16;
+    fn write_pixel(&mut self, x: u16, y: u16, color: u32);
+    fn fill_rect(&mut self, x: u16, y: u16, w: u16, h: u16, color: u32);
+    fn clear(&mut self, color: u32);
+    fn flush(&mut self);
+}

crates/ports/input-device/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "port-input-device"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

crates/ports/input-device/src/lib.rs

@@ -0,0 +1,54 @@
+#![no_std]
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Key {
+    Up,
+    Down,
+    Left,
+    Right,
+    Enter,
+    Escape,
+    Space,
+    Backspace,
+    Tab,
+    Char(u8),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum GamepadButton {
+    South,
+    East,
+    North,
+    West,
+    DpadUp,
+    DpadDown,
+    DpadLeft,
+    DpadRight,
+    Start,
+    Select,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Axis {
+    LeftX,
+    LeftY,
+    RightX,
+    RightY,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum InputEvent {
+    KeyDown(Key),
+    KeyUp(Key),
+    PointerDown { id: u8, x: u16, y: u16 },
+    PointerMove { id: u8, x: u16, y: u16 },
+    PointerUp { id: u8, x: u16, y: u16 },
+    Scroll { dx: i16, dy: i16 },
+    GamepadButton { button: GamepadButton, pressed: bool },
+    GamepadAxis { axis: Axis, value: i16 },
+}
+
+pub trait InputDevice {
+    fn poll(&mut self) -> Option<InputEvent>;
+    fn has_event(&self) -> bool;
+}