fix(security): remove error details from HTTP 500 response (#12)

The 500 error response previously included the raw error message {e}
in the body, potentially leaking internal implementation details (SDP
parse errors, ICE candidate info) to clients.

The detailed error is already logged server-side via tracing::error!,
so the response body is now a fixed generic string with a proper
HTTP/1.1 status line.

src/webrtc.rs

@@ -210,7 +210,7 @@ impl WebRtcState {
                     }
                     Err(e) => {
                         tracing::error!("SDP offer handling failed: {e}");
-                        let resp = format!("HTTP/1.1 500 Error\r\nConnection: close\r\n\r\n{e}");
+                        let resp = "HTTP/1.1 500 Internal Server Error\r\nConnection: close\r\n\r\n";
                         let _ = stream.write_all(resp.as_bytes());
                     }
                 }
@@ -311,18 +311,14 @@ impl WebRtcInner {
     }
 
     fn discover_video_params(&mut self) {
-        for s in ["0", "1", "2", "3"] {
-            let mid: Mid = s.into();
-            if let Some(media) = self.rtc.media(mid) {
-                if media.kind() == MediaKind::Video {
-                    tracing::info!("Found video media: mid={mid}");
-                    self.video_mid = Some(mid);
-                    break;
+        let mid = match self.video_mid {
+            Some(m) => m,
+            None => {
+                tracing::warn!("discover_video_params: no video_mid yet");
+                return;
             }
-            }
-        }
-
-        if let Some(mid) = self.video_mid {
+        };
+        self.video_pt = None;
         if let Some(writer) = self.rtc.writer(mid) {
             for pp in writer.payload_params() {
                 tracing::debug!("Codec: pt={:?} spec={:?}", pp.pt(), pp.spec());
@@ -333,6 +329,8 @@ impl WebRtcInner {
                 }
             }
         }
+        if self.video_pt.is_none() {
+            tracing::warn!("discover_video_params: no H.264 codec found for mid={mid}");
         }
     }
 
@@ -357,9 +355,21 @@ impl WebRtcInner {
                         Event::IceConnectionStateChange(IceConnectionState::Disconnected) => {
                             tracing::warn!("WebRTC disconnected");
                             self.connected = false;
+                            return Ok(true);
                         }
                         Event::MediaAdded(ma) => {
-                            tracing::info!("Media added: mid={:?}", ma.mid);
+                            tracing::info!("Media added: mid={} kind={:?}", ma.mid, ma.kind);
+                            if ma.kind == MediaKind::Video {
+                                if let Some(media) = self.rtc.media(ma.mid) {
+                                    if media.direction().is_sending()
+                                        && self.video_mid.is_none()
+                                    {
+                                        self.video_mid = Some(ma.mid);
+                                        tracing::info!("Captured video mid: {}", ma.mid);
+                                        self.discover_video_params();
+                                    }
+                                }
+                            }
                         }
                         _ => {
                             tracing::debug!("WebRTC event: {:?}", e);