fix(windows): do not panic in souvlaki without an HWND; open folders via open::that

souvlaki's Windows backend does config.hwnd.expect() at
platform/windows/mod.rs:57, so the None we passed was a panic inside a
tokio task on the first session, not the Err the match was written for.
The comment on that field claimed init would merely fail; it was read from
the comment, not the mechanism. No HWND is wired yet, so spawn() bows out
on Windows and the body moves to spawn_native, which is compiled out
there. Phase A ships without media keys and says so.

The offline-folder opener spawned xdg-open on every non-macOS host,
Windows included, where it does not exist. Route it through the open crate
like the other eleven sites in this crate; Linux and macOS reach the same
two binaries as before.

cc

crates/qbz-media-controls/src/platform.rs

@@ -8,14 +8,17 @@
 use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
-use souvlaki::{
-    MediaControlEvent, MediaControls, MediaMetadata, MediaPlayback, MediaPosition, PlatformConfig,
-    SeekDirection,
-};
+use souvlaki::{MediaControls, MediaMetadata, MediaPlayback, MediaPosition};
+// Only `spawn_native` and `map_event` touch these, and both are compiled out
+// on Windows (souvlaki's SMTC backend panics without an HWND — see `spawn`).
+#[cfg(not(target_os = "windows"))]
+use souvlaki::{MediaControlEvent, PlatformConfig, SeekDirection};
 
 use crate::types::{MediaEvent, MediaIntegration, PlaybackStatus, TrackMeta};
 
 /// Default step for a magnitude-less MPRIS-style `Seek` (5 seconds, micros).
+// Only `map_event` reads it, and that is compiled out on Windows.
+#[cfg(not(target_os = "windows"))]
 const SEEK_STEP_MICROS: i64 = 5_000_000;
 
 type EventCb = Arc<dyn Fn(MediaEvent) + Send + Sync>;
@@ -60,6 +63,8 @@ impl MediaIntegration for PlatformHandle {
     }
 }
 
+// Only `spawn_native` installs it, and that is compiled out on Windows.
+#[cfg(not(target_os = "windows"))]
 fn map_event(e: MediaControlEvent) -> Option<MediaEvent> {
     Some(match e {
         MediaControlEvent::Play => MediaEvent::Play,
@@ -86,11 +91,32 @@ fn map_event(e: MediaControlEvent) -> Option<MediaEvent> {
 }
 
 pub fn spawn(on_event: EventCb) -> Option<PlatformHandle> {
+    // souvlaki's Windows backend does NOT degrade gracefully without an HWND:
+    // `config.hwnd.expect(...)` at souvlaki-0.8.3/src/platform/windows/mod.rs:57-59
+    // PANICS, and `MediaControls::new` runs inside a tokio task, so the first
+    // session would abort the task rather than return the Err the match below
+    // is written for. (The old comment on `hwnd: None` claimed the opposite;
+    // it was read from the comment, not the mechanism.) No HWND is wired yet
+    // — that is plan A-2's "SMTC real" task — so bow out here on Windows.
+    #[cfg(target_os = "windows")]
+    {
+        let _ = on_event;
+        log::warn!("[media-controls] SMTC disabled: no window handle wired yet (Phase A)");
+        return None;
+    }
+    #[cfg(not(target_os = "windows"))]
+    {
+        return spawn_native(on_event);
+    }
+}
+
+#[cfg(not(target_os = "windows"))]
+fn spawn_native(on_event: EventCb) -> Option<PlatformHandle> {
     let config = PlatformConfig {
         dbus_name: "com.blitzfc.qbz",
         display_name: "QBZ",
-        // macOS: unused. Windows SMTC needs the window HWND; not shipped/tested,
-        // so left None (init may fail there → None handle, no media controls).
+        // macOS: unused. Windows: unreachable — see the early return in
+        // `spawn` above.
         hwnd: None,
     };
 

crates/qbz-qt/src/offline_cache_qt.rs

@@ -377,21 +377,19 @@ pub fn remove_album(album_id: String) {
 
 /// Open the cache directory in the desktop file manager (Slint `open_folder`).
 ///
-/// `xdg-open` / `open` by hand rather than the `rfd` used elsewhere in the
-/// port: rfd opens a PICKER, and this row is "show me the folder". Same two
-/// binaries the reference shells out to.
+/// Not the `rfd` used elsewhere in the port: rfd opens a PICKER, and this row
+/// is "show me the folder". Routed through the `open` crate like the other
+/// eleven sites in this crate — the hand-rolled `xdg-open` fallback ran on
+/// every non-macOS host, Windows included, where it does not exist. `open`
+/// uses ShellExecuteW there and xdg-open/open on Linux/macOS, so the two
+/// supported platforms behave exactly as before.
 pub fn open_folder() {
     crate::spawn(async move {
         let Some(off) = offline_qt::get().await else {
             return;
         };
         let path = off.get_cache_path();
-        let opener = if cfg!(target_os = "macos") {
-            "open"
-        } else {
-            "xdg-open"
-        };
-        if let Err(e) = std::process::Command::new(opener).arg(&path).spawn() {
+        if let Err(e) = open::that(&path) {
             log::warn!("[qbz-qt] open offline folder failed: {e}");
         }
     });