agent: wayland — evdev hotkey backend, download resume, SHA256 integrity

Add kon-hotkey crate with evdev-based global hotkey capture that works on
Wayland (and X11). Patterns from whisper-overlay: per-device async listeners,
inotify hotplug with udev permission retry, watch channel for live config
updates. Frontend detects Wayland at startup and selects evdev or
tauri-plugin-global-shortcut automatically.

Model downloads now support HTTP Range resume for interrupted downloads and
optional SHA256 integrity verification (incremental, no second pass).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/hotkey/src/lib.rs

@@ -0,0 +1,138 @@
+//! Wayland-compatible global hotkey listener for Kon.
+//!
+//! On Linux, reads `/dev/input/event*` devices via the `evdev` crate to capture
+//! global hotkeys without any display-server dependency. This works on both X11
+//! and Wayland, but requires the user to be in the `input` group (or have read
+//! access to `/dev/input/`).
+//!
+//! On non-Linux platforms, this crate is a no-op — the Tauri global-shortcut
+//! plugin handles hotkeys there.
+//!
+//! Architecture stolen from oddlama/whisper-overlay and adapted for Kon.
+
+#[cfg(target_os = "linux")]
+mod linux;
+
+#[cfg(target_os = "linux")]
+pub use linux::*;
+
+#[cfg(not(target_os = "linux"))]
+mod stub;
+
+#[cfg(not(target_os = "linux"))]
+pub use stub::*;
+
+use serde::{Deserialize, Serialize};
+
+/// A hotkey combination: one or more modifiers + a trigger key.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct HotkeyCombo {
+    pub ctrl: bool,
+    pub shift: bool,
+    pub alt: bool,
+    pub super_key: bool,
+    /// The evdev key code for the trigger key (e.g. KEY_R = 19).
+    /// On the frontend, this is mapped from the key name.
+    pub key_code: u16,
+    /// Human-readable label for display (e.g. "Ctrl+Shift+R").
+    pub label: String,
+}
+
+impl HotkeyCombo {
+    /// Parse a Tauri-style hotkey string like "Ctrl+Shift+R" into a HotkeyCombo.
+    /// Returns None if the string can't be parsed.
+    pub fn from_tauri_str(s: &str) -> Option<Self> {
+        let parts: Vec<&str> = s.split('+').map(|p| p.trim()).collect();
+        if parts.is_empty() {
+            return None;
+        }
+
+        let mut ctrl = false;
+        let mut shift = false;
+        let mut alt = false;
+        let mut super_key = false;
+        let mut trigger: Option<&str> = None;
+
+        for part in &parts {
+            match part.to_lowercase().as_str() {
+                "ctrl" | "control" => ctrl = true,
+                "shift" => shift = true,
+                "alt" => alt = true,
+                "super" | "meta" | "cmd" | "command" => super_key = true,
+                _ => trigger = Some(part),
+            }
+        }
+
+        let key_name = trigger?;
+        let key_code = key_name_to_evdev_code(key_name)?;
+
+        Some(Self {
+            ctrl,
+            shift,
+            alt,
+            super_key,
+            key_code,
+            label: s.to_string(),
+        })
+    }
+}
+
+/// Map a key name (from the frontend) to an evdev key code.
+/// Covers the keys likely to be used in hotkey combos.
+fn key_name_to_evdev_code(name: &str) -> Option<u16> {
+    // evdev key codes from linux/input-event-codes.h
+    Some(match name.to_uppercase().as_str() {
+        "A" => 30, "B" => 48, "C" => 46, "D" => 32, "E" => 18,
+        "F" => 33, "G" => 34, "H" => 35, "I" => 23, "J" => 36,
+        "K" => 37, "L" => 38, "M" => 50, "N" => 49, "O" => 24,
+        "P" => 25, "Q" => 16, "R" => 19, "S" => 31, "T" => 20,
+        "U" => 22, "V" => 47, "W" => 17, "X" => 45, "Y" => 21,
+        "Z" => 44,
+        "1" => 2, "2" => 3, "3" => 4, "4" => 5, "5" => 6,
+        "6" => 7, "7" => 8, "8" => 9, "9" => 10, "0" => 11,
+        "F1" => 59, "F2" => 60, "F3" => 61, "F4" => 62,
+        "F5" => 63, "F6" => 64, "F7" => 65, "F8" => 66,
+        "F9" => 67, "F10" => 68, "F11" => 87, "F12" => 88,
+        "SPACE" | " " => 57,
+        "ESCAPE" | "ESC" => 1,
+        "TAB" => 15,
+        "BACKSPACE" => 14,
+        "ENTER" | "RETURN" => 28,
+        "DELETE" => 111,
+        "HOME" => 102, "END" => 107,
+        "PAGEUP" => 104, "PAGEDOWN" => 109,
+        "UP" | "ARROWUP" => 103,
+        "DOWN" | "ARROWDOWN" => 108,
+        "LEFT" | "ARROWLEFT" => 105,
+        "RIGHT" | "ARROWRIGHT" => 106,
+        "INSERT" => 110,
+        "PAUSE" => 119,
+        "SCROLLLOCK" => 70,
+        "PRINTSCREEN" => 99,
+        "`" | "BACKQUOTE" => 41,
+        "-" | "MINUS" => 12,
+        "=" | "EQUAL" => 13,
+        "[" | "BRACKETLEFT" => 26,
+        "]" | "BRACKETRIGHT" => 27,
+        "\\" | "BACKSLASH" => 43,
+        ";" | "SEMICOLON" => 39,
+        "'" | "QUOTE" => 40,
+        "," | "COMMA" => 51,
+        "." | "PERIOD" => 52,
+        "/" | "SLASH" => 53,
+        _ => return None,
+    })
+}
+
+/// Check whether the current user can read evdev devices.
+/// Returns a diagnostic message if not.
+pub fn check_evdev_access() -> Result<(), String> {
+    #[cfg(target_os = "linux")]
+    {
+        linux::check_access()
+    }
+    #[cfg(not(target_os = "linux"))]
+    {
+        Err("evdev hotkeys are only supported on Linux".to_string())
+    }
+}