fix: address PR #264 review issues

- Fix connectDesktopStream silently dropping RTCPeerConnection and rtcConfig options (client.ts)
- Fix DesktopViewer useEffect dependency causing reconnect loop (store callbacks in refs)
- Fix TOCTOU race condition in DesktopRecordingManager::start() (merge lock scope)
- Fix incomplete cursor bounds check in composite_cursor_region (add right/bottom checks)
- Add DesktopViewer to react-components.mdx documentation
- Remove hardcoded visual styles from DesktopViewer (make unstyled by default per sdks/CLAUDE.md)
- Export DesktopViewerClassNames type for consumer styling

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

server/packages/sandbox-agent/src/desktop_recording.rs

@@ -64,17 +64,13 @@ impl DesktopRecordingManager {
 
         self.ensure_recordings_dir()?;
 
-        {
-            let mut state = self.inner.lock().await;
-            self.refresh_locked(&mut state).await?;
-            if state.current_id.is_some() {
-                return Err(SandboxError::Conflict {
-                    message: "a desktop recording is already active".to_string(),
-                });
-            }
-        }
-
         let mut state = self.inner.lock().await;
+        self.refresh_locked(&mut state).await?;
+        if state.current_id.is_some() {
+            return Err(SandboxError::Conflict {
+                message: "a desktop recording is already active".to_string(),
+            });
+        }
         let id_num = state.next_id + 1;
         state.next_id = id_num;
         let id = format!("rec_{id_num}");

server/packages/sandbox-agent/src/desktop_runtime.rs

@@ -2036,14 +2036,18 @@ impl DesktopRuntime {
         options: &DesktopScreenshotOptions,
         region_x: i32,
         region_y: i32,
-        _region_width: u32,
-        _region_height: u32,
+        region_width: u32,
+        region_height: u32,
     ) -> Result<Vec<u8>, DesktopProblem> {
         let pos = self.mouse_position_locked(state, ready).await?;
         // Adjust cursor position relative to the region
         let cursor_x = pos.x - region_x;
         let cursor_y = pos.y - region_y;
-        if cursor_x < 0 || cursor_y < 0 {
+        if cursor_x < 0
+            || cursor_y < 0
+            || cursor_x >= region_width as i32
+            || cursor_y >= region_height as i32
+        {
             // Cursor is outside the region, return screenshot as-is
             return Ok(screenshot_bytes);
         }