fix(state_portal): replace expect() with bail-style error propagation (closes #9)

src/state_portal.rs

@@ -164,7 +164,8 @@ impl StatePortal {
 
                 // 根据是否启用 WebRTC 选择不同的编码器构造方式
                 let enc = if let Some(ref tx) = self.webrtc_tx {
-                    let paused = self.webrtc_paused.as_ref().expect("webrtc_paused must exist when webrtc_tx exists");
+                    let paused = self.webrtc_paused.as_ref()
+                        .ok_or_else(|| anyhow::anyhow!("internal invariant broken: webrtc_paused missing while WebRTC mode is active"))?;
                     avhw::SwEncState::new_webrtc(
                         &drm_path,
                         frame.width,
@@ -179,9 +180,11 @@ impl StatePortal {
                     )?
                 } else {
                     // MP4 模式：编码输出写入文件
+                    let output_path = self.args.output.as_deref()
+                        .ok_or_else(|| anyhow::anyhow!("--output is required in MP4 file output mode; use --port > 0 for WebRTC mode"))?;
                     avhw::SwEncState::new(
                         &drm_path,
-                        std::path::Path::new(self.args.output.as_deref().expect("output required for MP4 mode")),
+                        std::path::Path::new(output_path),
                         frame.width,
                         frame.height,
                         enc_width,