fix: 修复 waitForProcess race condition，添加调试日志

Sources/StreamRecorderKit/FFmpegRecorder.swift

@@ -15,6 +15,21 @@ final class ProgressState: @unchecked Sendable {
     }
 }
 
+/// Thread-safe atomic boolean for one-shot guards
+final class AtomicBool: @unchecked Sendable {
+    private var value = false
+    private let lock = NSLock()
+    
+    /// Returns true if this call set it from false to true (first caller wins)
+    func setTrue() -> Bool {
+        lock.lock()
+        defer { lock.unlock() }
+        guard !value else { return false }
+        value = true
+        return true
+    }
+}
+
 public final class FFmpegRecorder: StreamRecorderEngine {
     public weak var delegate: StreamRecorderDelegate?
     public private(set) var isRecording = false
@@ -108,6 +123,7 @@ public final class FFmpegRecorder: StreamRecorderEngine {
         
         // 异步等待进程完成（不阻塞 cooperative thread）
         await waitForProcess(proc)
+        NSLog("[Recorder] ffmpeg process exited, status: %d", proc.terminationStatus)
         stderrPipe.fileHandleForReading.readabilityHandler = nil
         isRecording = false
         
@@ -119,9 +135,11 @@ public final class FFmpegRecorder: StreamRecorderEngine {
             throw RecordingError.outputNotFound
         }
         
+        NSLog("[Recorder] Analyzing output file...")
         // 分析输出文件
         let ffprobePath = ffmpegPath.replacingOccurrences(of: "ffmpeg", with: "ffprobe")
         let result = try await analyzeOutput(path: outputPath, ffprobePath: ffprobePath)
+        NSLog("[Recorder] Analysis complete, notifying delegate")
         delegate?.recorder(self, didFinishWithResult: result)
     }
     
@@ -141,13 +159,18 @@ public final class FFmpegRecorder: StreamRecorderEngine {
     private func waitForProcess(_ proc: Process) async {
         guard proc.isRunning else { return }
         await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
+            let resumed = AtomicBool()
             proc.terminationHandler = { _ in
-                continuation.resume()
+                if resumed.setTrue() {
+                    continuation.resume()
+                }
             }
             // Race condition: process may have exited between isRunning check and setting handler
             if !proc.isRunning {
                 proc.terminationHandler = nil
-                continuation.resume()
+                if resumed.setTrue() {
+                    continuation.resume()
+                }
             }
         }
     }