feat(app): desktop notifications on Windows

Toasts through WinRT, under the app id io.narl.proton-stream. The id is
registered for the current user under HKCU\Software\Classes\AppUserModelId
with a display name and icon on the first notification of a session, which
is what lets an app with no package or installer-made shortcut show one. If
that write fails, the toast goes out under PowerShell's id rather than not
at all.

Cargo.lock

@@ -4422,6 +4422,7 @@ dependencies = [
  "serde_json",
  "sha2 0.10.9",
  "souvlaki",
+ "tauri-winrt-notification",
  "tokio",
  "tracing",
  "tracing-subscriber",
@@ -5544,7 +5545,7 @@ dependencies = [
  "dispatch",
  "objc",
  "thiserror 1.0.69",
- "windows",
+ "windows 0.44.0",
 ]
 
 [[package]]
@@ -5635,6 +5636,17 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "55937e1799185b12863d447f42597ed69d9928686b8d88a1df17376a097d8369"
 
+[[package]]
+name = "tauri-winrt-notification"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f37a6c354fd28fc9e322ed9bd47e3959576dad28c9d58ea1cf888cce1c7ccb36"
+dependencies = [
+ "thiserror 2.0.19",
+ "windows 0.62.2",
+ "windows-version",
+]
+
 [[package]]
 name = "tempfile"
 version = "3.27.0"
@@ -6695,6 +6707,27 @@ dependencies = [
  "windows-targets 0.42.2",
 ]
 
+[[package]]
+name = "windows"
+version = "0.62.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "527fadee13e0c05939a6a05d5bd6eec6cd2e3dbd648b9f8e447c6518133d8580"
+dependencies = [
+ "windows-collections",
+ "windows-core",
+ "windows-future",
+ "windows-numerics",
+]
+
+[[package]]
+name = "windows-collections"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23b2d95af1a8a14a3c7367e1ed4fc9c20e0a26e79551b1454d72583c97cc6610"
+dependencies = [
+ "windows-core",
+]
+
 [[package]]
 name = "windows-core"
 version = "0.62.2"
@@ -6708,6 +6741,17 @@ dependencies = [
  "windows-strings",
 ]
 
+[[package]]
+name = "windows-future"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1d6f90251fe18a279739e78025bd6ddc52a7e22f921070ccdc67dde84c605cb"
+dependencies = [
+ "windows-core",
+ "windows-link",
+ "windows-threading",
+]
+
 [[package]]
 name = "windows-implement"
 version = "0.60.2"
@@ -6736,6 +6780,16 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
 
+[[package]]
+name = "windows-numerics"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e2e40844ac143cdb44aead537bbf727de9b044e107a0f1220392177d15b0f26"
+dependencies = [
+ "windows-core",
+ "windows-link",
+]
+
 [[package]]
 name = "windows-result"
 version = "0.4.1"
@@ -6871,6 +6925,24 @@ dependencies = [
  "windows_x86_64_msvc 0.53.1",
 ]
 
+[[package]]
+name = "windows-threading"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3949bd5b99cafdf1c7ca86b43ca564028dfe27d66958f2470940f73d86d75b37"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-version"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e4060a1da109b9d0326b7262c8e12c84df67cc0dbc9e33cf49e01ccc2eb63631"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "windows_aarch64_gnullvm"
 version = "0.42.2"

Cargo.toml

@@ -98,6 +98,8 @@ souvlaki = { version = "0.8", default-features = false, features = ["use_dbus"]
 # hold it for.
 dbus = "0.9"
 windows-sys = "0.61"
+# Toasts on Windows. Linux notifications go over the `dbus` above.
+tauri-winrt-notification = "0.8"
 rpassword = "7"
 libloading = "0.8"
 lru = "0.12"

crates/pstr-app/Cargo.toml

@@ -40,5 +40,6 @@ dbus.workspace = true
 [target.'cfg(windows)'.dependencies]
 # Named pipes, for handing a second launch's request to the open window.
 tokio = { workspace = true, features = ["net"] }
-windows-sys = { workspace = true, features = ["Win32_System_Power"] }
+windows-sys = { workspace = true, features = ["Win32_System_Power", "Win32_System_Registry"] }
+tauri-winrt-notification.workspace = true
 raw-window-handle = "0.6"

crates/pstr-app/src/app.rs

@@ -508,6 +508,7 @@ impl App {
         // theme, and a window that paints one frame in the default palette
         // before switching is a window that flashes on every launch.
         let window = crate::window::WindowMemory::new(dirs.window_file());
+        let notifier = crate::notify::Notifier::new(&dirs.cache);
         let (engine, events) = Engine::new(runtime, dirs, cc.egui_ctx.clone())?;
         theme::install_fonts(&cc.egui_ctx);
         theme::apply(&cc.egui_ctx, engine.appearance());
@@ -558,7 +559,7 @@ impl App {
             media_cover: None,
             inhibitor: crate::inhibit::Inhibitor::new(),
             shown_page: (None, 0.0),
-            notifier: crate::notify::Notifier::new(),
+            notifier,
             downloads: Vec::new(),
             offline_files: std::collections::HashSet::new(),
             confirm_partial_delete: None,

crates/pstr-app/src/notify.rs

@@ -4,41 +4,48 @@
 //! app already has the toast, and a second copy of it from the panel is noise.
 //! That rule is the caller's — see `App::notify`.
 //!
-//! Linux only, over `org.freedesktop.Notifications`. Windows wants an
-//! application id registered by an installer before a toast will show, and a
-//! notification that silently never appears is worse than none.
+//! Linux over `org.freedesktop.Notifications`; Windows as a toast. Nothing on
+//! macOS yet.
+//!
+//! A Windows toast is shown under an application id, and Windows drops a toast
+//! whose id it does not know without a word. The id is registered for the
+//! current user under `HKCU\Software\Classes\AppUserModelId` — the same
+//! registration the Windows App SDK makes for an app with no package — which
+//! works for the MSI and the portable zip alike. If that write fails, the
+//! toast goes out under PowerShell's id instead, which Windows always knows: a
+//! notification that names the wrong program beats one that never appears.
+
+use std::path::Path;
 
 /// Sends notifications from a thread of its own, so a notification daemon
 /// that is slow to answer never costs a frame.
 pub struct Notifier {
-    #[cfg(target_os = "linux")]
+    #[cfg(any(target_os = "linux", windows))]
     orders: Option<std::sync::mpsc::Sender<(String, String)>>,
 }
 
 impl Notifier {
-    pub fn new() -> Self {
+    /// `cache` is where Windows is pointed for the toast's icon.
+    pub fn new(cache: &Path) -> Self {
+        let _ = cache;
         Self {
             #[cfg(target_os = "linux")]
             orders: linux::spawn(),
+            #[cfg(windows)]
+            orders: windows::spawn(cache.join("notification-icon.png")),
         }
     }
 
     pub fn send(&self, summary: impl Into<String>, body: impl Into<String>) {
-        #[cfg(target_os = "linux")]
+        #[cfg(any(target_os = "linux", windows))]
         if let Some(orders) = &self.orders {
             let _ = orders.send((summary.into(), body.into()));
         }
-        #[cfg(not(target_os = "linux"))]
+        #[cfg(not(any(target_os = "linux", windows)))]
         let _ = (summary.into(), body.into());
     }
 }
 
-impl Default for Notifier {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 #[cfg(target_os = "linux")]
 mod linux {
     use std::sync::mpsc::{Sender, channel};
@@ -93,3 +100,91 @@ mod linux {
         Some(orders)
     }
 }
+
+#[cfg(windows)]
+mod windows {
+    use std::path::{Path, PathBuf};
+    use std::sync::mpsc::{Sender, channel};
+
+    use tauri_winrt_notification::Toast;
+
+    /// The id toasts are shown under, and the key it is registered at.
+    const APP_ID: &str = "io.narl.proton-stream";
+    const ICON: &[u8] = include_bytes!("../assets/icon-256.png");
+
+    pub fn spawn(icon: PathBuf) -> Option<Sender<(String, String)>> {
+        let (orders, receiver) = channel::<(String, String)>();
+        std::thread::Builder::new()
+            .name("notify".into())
+            .spawn(move || {
+                // Registered on first use rather than at startup: most
+                // sessions never send one.
+                let mut app_id: Option<&str> = None;
+                for (summary, body) in receiver {
+                    let id = *app_id.get_or_insert_with(|| {
+                        let _ = std::fs::write(&icon, ICON);
+                        if register(&icon) {
+                            APP_ID
+                        } else {
+                            Toast::POWERSHELL_APP_ID
+                        }
+                    });
+                    let shown = Toast::new(id).title(&summary).text1(&body).show();
+                    if let Err(error) = shown {
+                        tracing::debug!("notification: {error}");
+                    }
+                }
+            })
+            .inspect_err(|error| tracing::debug!("notify thread: {error}"))
+            .ok()?;
+        Some(orders)
+    }
+
+    /// Tell Windows the app id's display name and icon. Per user, no rights
+    /// needed, and written again every session so a moved install points at
+    /// a live icon.
+    fn register(icon: &Path) -> bool {
+        use windows_sys::Win32::System::Registry::{
+            HKEY, HKEY_CURRENT_USER, KEY_WRITE, REG_OPTION_NON_VOLATILE, REG_SZ, RegCloseKey,
+            RegCreateKeyExW, RegSetValueExW,
+        };
+
+        fn wide(text: &str) -> Vec<u16> {
+            text.encode_utf16().chain(std::iter::once(0)).collect()
+        }
+
+        let path = wide(&format!(r"Software\Classes\AppUserModelId\{APP_ID}"));
+        let mut key: HKEY = std::ptr::null_mut();
+        // SAFETY: every pointer is to a live, NUL-terminated buffer or an out
+        // parameter on this stack frame, and the key is closed before return.
+        unsafe {
+            let created = RegCreateKeyExW(
+                HKEY_CURRENT_USER,
+                path.as_ptr(),
+                0,
+                std::ptr::null(),
+                REG_OPTION_NON_VOLATILE,
+                KEY_WRITE,
+                std::ptr::null(),
+                &mut key,
+                std::ptr::null_mut(),
+            );
+            if created != 0 {
+                tracing::debug!("register the notification id: error {created}");
+                return false;
+            }
+            let icon = icon.to_string_lossy();
+            let mut written = true;
+            for (name, value) in [("DisplayName", "Proton Stream"), ("IconUri", icon.as_ref())] {
+                let name = wide(name);
+                let value = wide(value);
+                let bytes = u32::try_from(value.len() * 2).unwrap_or(u32::MAX);
+                let set =
+                    RegSetValueExW(key, name.as_ptr(), 0, REG_SZ, value.as_ptr().cast(), bytes);
+                written &= set == 0;
+            }
+            RegCloseKey(key);
+            written
+        }
+    }
+}

docs/ARCHITECTURE.md

@@ -125,3 +125,4 @@ an edge case.
 | Desktop-only settings | config dir, `desktop.json` | Defaults if missing — hardware decoding, cache budget; never overwritten when unparseable |
 | Window size | config dir, `window.json` | Defaults if missing or implausible |
 | Single-instance pipe key (Windows) | config dir, `instance.key` | Yes — regenerated if missing |
+| Notification app id (Windows) | `HKCU\Software\Classes\AppUserModelId\io.narl.proton-stream`, icon in cache dir | Yes — written again the first time a session notifies |