feat: add WebRTC streaming via str0m + portal session persistence

- Add src/webrtc.rs: HTTP signaling server + str0m Sans-IO WebRTC transport
  with H.264 Annex-B → RTP packetization and key-frame request handling
- avhw: introduce FrameOutput enum (Muxer | Channel) so SwEncState can
  output to either MP4 muxer or crossbeam channel for WebRTC
- cap_portal: support portal session restore tokens (PersistMode::ExplicitlyRevoked)
  to skip re-authorization dialog; add --no-persist flag to force fresh dialog
- args: make --output optional when --port is used for WebRTC mode
- state_portal: integrate WebRTC pipeline (encoder channel → RTP forwarding)
  with shorter GOP for WebRTC (fps/2, min 10)
- main: redirect tracing to stderr; validate --output or --port required
- Add dependencies: str0m 0.20, serde_json 1, dirs 6

src/cap_portal.rs

@@ -12,6 +12,7 @@
 //   - crossbeam-channel: 高性能有界通道，用于线程间帧传递
 
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd};
+use std::path::PathBuf;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
 use std::thread::{self, JoinHandle};
@@ -98,12 +99,10 @@ impl CapPortal {
     ///   4. 创建 eventfd 对，用于线程安全的关闭信号传递
     ///   5. 启动 PipeWire 捕获线程
     pub fn new(args: &Args) -> Result<Self> {
-        // 创建独立的 Tokio 运行时，仅用于 setup_portal 中的异步 Portal D-Bus 调用
         let rt = Runtime::new()?;
 
-        // 通过 Portal 获取 PipeWire 连接 fd 和节点 ID
-        // block_on 在此处同步等待异步 Portal 调用完成
-        let (pw_fd, node_id) = rt.block_on(async { Self::setup_portal().await })?;
+        let no_persist = args.no_persist;
+        let (pw_fd, node_id) = rt.block_on(async { Self::setup_portal(no_persist).await })?;
 
         let (frame_tx, frame_rx) = bounded(16);
         let (event_tx, event_rx) = bounded(8);
@@ -172,44 +171,50 @@ impl CapPortal {
     ///   5. 打开 PipeWire 远程连接，获取文件描述符
     ///
     /// 返回 (PipeWire fd, node_id)，供 PipeWire 线程连接使用
-    async fn setup_portal() -> Result<(OwnedFd, u32)> {
+    async fn setup_portal(no_persist: bool) -> Result<(OwnedFd, u32)> {
         use ashpd::desktop::screencast::{
             CursorMode, Screencast, SelectSourcesOptions, SourceType,
         };
         use ashpd::desktop::PersistMode;
 
-        // 创建 Screencast D-Bus 代理，与桌面环境的 Portal 服务通信
         let proxy = Screencast::new()
             .await
             .map_err(|e| anyhow::anyhow!("Failed to create Screencast proxy: {e}"))?;
 
-        // 创建 ScreenCast 会话（每个会话对应一次屏幕录制请求）
         let session = proxy
             .create_session(Default::default())
             .await
             .map_err(|e| anyhow::anyhow!("Failed to create ScreenCast session: {e}"))?;
 
-        // 配置录制源选择参数:
-        //   - CursorMode::Embedded: 光标嵌入到帧数据中（而非单独的元数据）
-        //   - SourceType::Monitor: 仅捕获显示器（不捕获窗口）
-        //   - multiple: false: 不允许多源选择
-        //   - PersistMode::DoNot: 不持久化会话（每次需要重新授权）
+        let version_supported = proxy.version() >= 4;
+
+        let (persist_mode, saved_token) = if !no_persist && version_supported {
+            let token = load_restore_token();
+            if token.is_some() {
+                tracing::info!("Attempting to restore portal session with saved token");
+            }
+            (PersistMode::ExplicitlyRevoked, token)
+        } else {
+            (PersistMode::DoNot, None)
+        };
+
+        let mut options = SelectSourcesOptions::default()
+            .set_cursor_mode(CursorMode::Embedded)
+            .set_sources(ashpd::enumflags2::BitFlags::from(SourceType::Monitor))
+            .set_multiple(false)
+            .set_persist_mode(persist_mode);
+
+        if let Some(ref token) = saved_token {
+            options = options.set_restore_token(token.as_str());
+        }
+
         proxy
-            .select_sources(
-                &session,
-                SelectSourcesOptions::default()
-                    .set_cursor_mode(CursorMode::Embedded)
-                    .set_sources(ashpd::enumflags2::BitFlags::from(SourceType::Monitor))
-                    .set_multiple(false)
-                    .set_persist_mode(PersistMode::DoNot),
-            )
+            .select_sources(&session, options)
             .await
             .map_err(|e| {
-                anyhow::anyhow!("屏幕共享权限被拒绝 / Screen sharing permission denied: {e}")
+                anyhow::anyhow!("Screen sharing permission denied: {e}")
             })?;
 
-        // 启动录制会话，此时桌面环境会弹出权限确认对话框
-        // 用户确认后返回包含 PipeWire 流信息的响应
         let response = proxy
             .start(&session, None, Default::default())
             .await
@@ -217,18 +222,19 @@ impl CapPortal {
             .response()
             .map_err(|e| anyhow::anyhow!("ScreenCast response error: {e}"))?;
 
-        // 获取返回的第一个（也是唯一的）视频流
-        // 每个流对应一个 PipeWire 节点
+        if !no_persist && version_supported {
+            if let Some(new_token) = response.restore_token() {
+                save_restore_token(new_token);
+            }
+        }
+
         let stream = response
             .streams()
             .first()
             .ok_or_else(|| anyhow::anyhow!("No streams returned from ScreenCast"))?;
 
-        // 提取 PipeWire 节点 ID，用于后续连接到该节点的视频流
         let node_id = stream.pipe_wire_node_id();
 
-        // 打开 PipeWire 远程连接，获取文件描述符
-        // 这个 fd 允许直接与 PipeWire 守护进程通信
         let fd = proxy
             .open_pipe_wire_remote(&session, Default::default())
             .await
@@ -240,6 +246,30 @@ impl CapPortal {
     }
 }
 
+fn token_path() -> PathBuf {
+    let base = dirs::cache_dir()
+        .unwrap_or_else(|| PathBuf::from("/tmp"));
+    base.join("wl-webrtc").join("portal-restore-token")
+}
+
+fn load_restore_token() -> Option<String> {
+    let path = token_path();
+    let token = std::fs::read_to_string(&path).ok()?;
+    let trimmed = token.trim().to_string();
+    if trimmed.is_empty() { None } else { Some(trimmed) }
+}
+
+fn save_restore_token(token: &str) {
+    let path = token_path();
+    if let Some(parent) = path.parent() {
+        let _ = std::fs::create_dir_all(parent);
+    }
+    match std::fs::write(&path, token) {
+        Ok(()) => tracing::info!("Saved portal restore token"),
+        Err(e) => tracing::warn!("Failed to save restore token: {e}"),
+    }
+}
+
 impl Drop for CapPortal {
     /// 析构时安全关闭 PipeWire 线程
     ///