Rewrite srdwm in Rust: working X11 and Wayland backends, Lua config

The C++ prototype (moved to legacy-cpp/) was mostly a design skeleton:
X11 and Windows backends were partially real, Wayland created the
wlroots object graph but never wired a single event listener, macOS
was stub except monitor enumeration, and the Lua engine's srd.bind()
stored a key-combo string but never the actual closure. See
docs/PRIOR_ART.md for the full audit.

This replaces it with a Cargo workspace:

- srdwm-core: platform-independent window/workspace/monitor state,
  a real master-stack tiling layout, and SmartPlacement grid/cascade/
  snap-to-edge placement - fixing several bugs in the C++ version
  (hardcoded 2-column grid, cascade that never cascaded, snap-to-edge
  that always returned a fixed rect). 35 unit tests.
- srdwm-config: the srd Lua API via mlua, implementing the surface
  docs/DEFAULTS.md always documented but the C++ engine never actually
  built (srd.window.close()/focus(direction), srd.workspace.next(),
  real keybinding closures, require("srd") support). 10 unit tests.
- srdwm-x11: a real reparenting WM with a drawn title bar (buttons,
  drag, resize), verified live under Xephyr - frame placement and
  client offset match srdwm-core's computed geometry exactly, and the
  decoration renders correctly on screen.
- srdwm-wayland: a from-scratch smithay compositor (the C++ version
  had nothing working to port from) - runs via the winit backend,
  tracks xdg-shell toplevels through the same WindowManager and
  hit-testing code X11 uses, verified to start/render/run without
  crashing. Decorations are solid-color (no text yet); see
  docs/IMPLEMENTATION_STATUS.md for exact scope.
- srdwm-windows / srdwm-macos: structured, cfg-gated designs informed
  by komorebi/glazewm and yabai/AeroSpace respectively (see
  docs/PRIOR_ART.md), honestly marked as unbuilt/unverified since this
  sandbox has no Windows or macOS target.

1 files changed, 112 insertions, 0 deletions

diff --git a/crates/x11/src/keysyms.rs b/crates/x11/src/keysyms.rs
new file mode 100644
index 0000000..0baa6bc
--- /dev/null
+++ b/crates/x11/src/keysyms.rs
@@ -0,0 +1,112 @@
+//! A small, hand-maintained keysym <-> name table covering the keys used in
+//! practice by window-manager keybindings (letters, digits, navigation,
+//! function keys). Not a full xkbcommon-level keymap - see module docs in
+//! `lib.rs` for why that trade-off was made for this pass.
+
+pub fn keysym_to_name(keysym: u32) -> Option<String> {
+    Some(match keysym {
+        0x0020 => "Space".to_string(),
+        0x0061..=0x007a => (((keysym - 0x0061) as u8 + b'a') as char).to_string(),
+        0x0030..=0x0039 => (((keysym - 0x0030) as u8 + b'0') as char).to_string(),
+        0xff0d => "Return".to_string(),
+        0xff1b => "Escape".to_string(),
+        0xff09 => "Tab".to_string(),
+        0xff08 => "BackSpace".to_string(),
+        0xffff => "Delete".to_string(),
+        0xff51 => "Left".to_string(),
+        0xff52 => "Up".to_string(),
+        0xff53 => "Right".to_string(),
+        0xff54 => "Down".to_string(),
+        0xff55 => "Prior".to_string(),
+        0xff56 => "Next".to_string(),
+        0xff50 => "Home".to_string(),
+        0xff57 => "End".to_string(),
+        0xffbe..=0xffc9 => format!("F{}", keysym - 0xffbe + 1),
+        0x1008ff13 => "XF86AudioRaiseVolume".to_string(),
+        0x1008ff11 => "XF86AudioLowerVolume".to_string(),
+        0x1008ff12 => "XF86AudioMute".to_string(),
+        0x1008ff02 => "XF86MonBrightnessUp".to_string(),
+        0x1008ff03 => "XF86MonBrightnessDown".to_string(),
+        _ => return None,
+    })
+}
+
+/// Case-insensitive: config authors reasonably write both `"Space"` and
+/// `"space"`, and X11 key names aren't consistently capitalized in the wild.
+pub fn name_to_keysym(name: &str) -> Option<u32> {
+    match name.to_ascii_lowercase().as_str() {
+        "space" => return Some(0x0020),
+        "return" | "enter" => return Some(0xff0d),
+        "escape" => return Some(0xff1b),
+        "tab" => return Some(0xff09),
+        "backspace" => return Some(0xff08),
+        "delete" => return Some(0xffff),
+        "left" => return Some(0xff51),
+        "up" => return Some(0xff52),
+        "right" => return Some(0xff53),
+        "down" => return Some(0xff54),
+        "prior" | "pageup" => return Some(0xff55),
+        "next" | "pagedown" => return Some(0xff56),
+        "home" => return Some(0xff50),
+        "end" => return Some(0xff57),
+        "xf86audioraisevolume" => return Some(0x1008ff13),
+        "xf86audiolowervolume" => return Some(0x1008ff11),
+        "xf86audiomute" => return Some(0x1008ff12),
+        "xf86monbrightnessup" => return Some(0x1008ff02),
+        "xf86monbrightnessdown" => return Some(0x1008ff03),
+        _ => {}
+    }
+    if name.len() == 1 {
+        let c = name.chars().next().unwrap().to_ascii_lowercase();
+        if c.is_ascii_lowercase() {
+            return Some(0x0061 + (c as u32 - 'a' as u32));
+        }
+        if c.is_ascii_digit() {
+            return Some(0x0030 + (c as u32 - '0' as u32));
+        }
+    }
+    if let Some(rest) = name.to_ascii_lowercase().strip_prefix('f') {
+        if let Ok(n) = rest.parse::<u32>() {
+            if (1..=12).contains(&n) {
+                return Some(0xffbe + n - 1);
+            }
+        }
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn letters_and_digits_roundtrip() {
+        for c in 'a'..='z' {
+            let name = c.to_string();
+            let ks = name_to_keysym(&name).unwrap();
+            assert_eq!(keysym_to_name(ks), Some(name));
+        }
+        for c in '0'..='9' {
+            let name = c.to_string();
+            let ks = name_to_keysym(&name).unwrap();
+            assert_eq!(keysym_to_name(ks), Some(name));
+        }
+    }
+
+    #[test]
+    fn lowercase_names_resolve_case_insensitively() {
+        // Config authors reasonably write "Mod4+Shift+space"; this must
+        // resolve to the same keysym as "Space".
+        assert_eq!(name_to_keysym("space"), name_to_keysym("Space"));
+        assert_eq!(name_to_keysym("return"), name_to_keysym("Return"));
+        assert_eq!(name_to_keysym("f5"), name_to_keysym("F5"));
+    }
+
+    #[test]
+    fn named_keys_roundtrip() {
+        for name in ["Return", "Escape", "Tab", "Left", "Right", "Up", "Down", "F1", "F12"] {
+            let ks = name_to_keysym(name).unwrap();
+            assert_eq!(keysym_to_name(ks), Some(name.to_string()));
+        }
+    }
+}