logiguard fork: GPUI xdg-activation keyboard-focus serial fix

Single-commit orphan branch: full zed-industries/zed @ 8c74db0 source tree
with a 3-file patch applied (no upstream history).

Patch (crates/gpui_linux/src/linux/wayland/):
  - serial.rs: add SerialKind::KeyboardEnter
  - client.rs: store wl_keyboard.enter serial; add latest_serial_of()
  - window.rs: activate() uses keyboard-enter serial (Mutter focus gate)

Mutter honors window activation only when the token carries the keyboard-
focus serial from wl_keyboard.enter; GPUI used a stale mouse-press serial.
See docs/tray-window-focus-wayland.md in logiguard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/env_var/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "env_var"
+version = "0.1.0"
+edition.workspace = true
+publish.workspace = true
+license = "GPL-3.0-or-later"
+
+[lints]
+workspace = true
+
+[lib]
+path = "src/env_var.rs"
+
+[dependencies]
+gpui_shared_string.workspace = true

crates/env_var/LICENSE-GPL

@@ -0,0 +1 @@
+../../LICENSE-GPL

crates/env_var/src/env_var.rs

@@ -0,0 +1,40 @@
+use gpui_shared_string::SharedString;
+
+#[derive(Clone)]
+pub struct EnvVar {
+    pub name: SharedString,
+    /// Value of the environment variable. Also `None` when set to an empty string.
+    pub value: Option<String>,
+}
+
+impl EnvVar {
+    pub fn new(name: SharedString) -> Self {
+        let value = std::env::var(name.as_str()).ok();
+        if value.as_ref().is_some_and(|v| v.is_empty()) {
+            Self { name, value: None }
+        } else {
+            Self { name, value }
+        }
+    }
+
+    pub fn or(self, other: EnvVar) -> EnvVar {
+        if self.value.is_some() { self } else { other }
+    }
+}
+
+/// Creates a `LazyLock<EnvVar>` expression for use in a `static` declaration.
+#[macro_export]
+macro_rules! env_var {
+    ($name:expr) => {
+        ::std::sync::LazyLock::new(|| $crate::EnvVar::new(($name).into()))
+    };
+}
+
+/// Generates a `LazyLock<bool>` expression for use in a `static` declaration. Checks if the
+/// environment variable exists and is non-empty.
+#[macro_export]
+macro_rules! bool_env_var {
+    ($name:expr) => {
+        ::std::sync::LazyLock::new(|| $crate::EnvVar::new(($name).into()).value.is_some())
+    };
+}