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>

src/routes/+layout.svelte

@@ -41,29 +41,89 @@
     }
   });
 
-  // Global hotkey registration
+  // Global hotkey registration — dual backend
+  // Wayland: evdev via kon-hotkey crate (works without display server)
+  // X11/macOS/Windows: tauri-plugin-global-shortcut (native)
   let registeredHotkey = null;
+  let hotkeyBackend = $state("unknown"); // "evdev" | "tauri" | "unavailable"
+
+  async function initHotkeyBackend() {
+    try {
+      const isWayland = await invoke("is_wayland_session");
+      if (isWayland) {
+        // Try evdev backend first (Wayland-compatible)
+        try {
+          await invoke("check_hotkey_access");
+          hotkeyBackend = "evdev";
+          console.log("Hotkey backend: evdev (Wayland)");
+        } catch (err) {
+          console.warn("evdev hotkey access denied:", err);
+          console.warn("Add your user to the 'input' group for global hotkeys on Wayland");
+          hotkeyBackend = "unavailable";
+        }
+      } else {
+        hotkeyBackend = "tauri";
+        console.log("Hotkey backend: tauri-plugin-global-shortcut (X11)");
+      }
+    } catch {
+      // Fallback to tauri plugin if detection fails
+      hotkeyBackend = "tauri";
+    }
+  }
 
   async function registerGlobalHotkey(hotkey) {
+    if (hotkeyBackend === "unknown") return; // not yet initialised
+
     try {
-      const mod = await import("@tauri-apps/plugin-global-shortcut");
-      if (registeredHotkey) {
-        await mod.unregister(registeredHotkey).catch(() => {});
-      }
-      await mod.register(hotkey, () => {
-        if (page.current !== "dictation") page.current = "dictation";
-        requestAnimationFrame(() => {
-          window.dispatchEvent(new CustomEvent("kon:toggle-recording"));
+      if (hotkeyBackend === "evdev") {
+        // evdev backend: start or update the Rust-side listener
+        if (registeredHotkey) {
+          await invoke("update_evdev_hotkey", { hotkey });
+        } else {
+          await invoke("start_evdev_hotkey", { hotkey });
+        }
+        registeredHotkey = hotkey;
+      } else if (hotkeyBackend === "tauri") {
+        // Tauri plugin backend (X11/macOS/Windows)
+        const mod = await import("@tauri-apps/plugin-global-shortcut");
+        if (registeredHotkey) {
+          await mod.unregister(registeredHotkey).catch(() => {});
+        }
+        await mod.register(hotkey, () => {
+          if (page.current !== "dictation") page.current = "dictation";
+          requestAnimationFrame(() => {
+            window.dispatchEvent(new CustomEvent("kon:toggle-recording"));
+          });
         });
-      });
-      registeredHotkey = hotkey;
+        registeredHotkey = hotkey;
+      }
     } catch (err) {
       console.error("Hotkey registration failed:", err);
     }
   }
 
+  // Listen for evdev hotkey events from the Rust backend
+  let unlistenEvdev = null;
+  async function setupEvdevListener() {
+    const { listen } = await import("@tauri-apps/api/event");
+    unlistenEvdev = await listen("kon:hotkey-pressed", () => {
+      if (page.current !== "dictation") page.current = "dictation";
+      requestAnimationFrame(() => {
+        window.dispatchEvent(new CustomEvent("kon:toggle-recording"));
+      });
+    });
+  }
+
   $effect(() => {
-    registerGlobalHotkey(settings.globalHotkey);
+    if (hotkeyBackend === "evdev" && !unlistenEvdev) {
+      setupEvdevListener();
+    }
+  });
+
+  $effect(() => {
+    if (hotkeyBackend !== "unknown") {
+      registerGlobalHotkey(settings.globalHotkey);
+    }
   });
 
   // Apply font size setting as CSS variable (legacy — kept for backwards compat)
@@ -100,6 +160,9 @@
     handleResize();
     window.addEventListener("resize", handleResize);
 
+    // Detect and initialise the correct hotkey backend
+    await initHotkeyBackend();
+
     try {
       const whisper = await invoke("list_models");
       const parakeet = await invoke("list_parakeet_models");
@@ -113,11 +176,16 @@
 
   onDestroy(() => {
     window.removeEventListener("resize", handleResize);
-    if (registeredHotkey) {
+    if (hotkeyBackend === "evdev") {
+      invoke("stop_evdev_hotkey").catch(() => {});
+    } else if (hotkeyBackend === "tauri" && registeredHotkey) {
       import("@tauri-apps/plugin-global-shortcut")
         .then((mod) => mod.unregister(registeredHotkey))
         .catch(() => {});
     }
+    if (unlistenEvdev) {
+      unlistenEvdev();
+    }
   });
 </script>