zero-alloc audio pipeline: pointer-based IO from ring buffer to stdout

Replace Data/AudioPacket allocations with raw pointer callbacks through
the entire audio pipeline. Ring buffer hands out direct pointers (or
linearizes into a pre-allocated scratch buffer on wrap-around), converter
accepts/emits pointers via its cached buffers, and output handler writes
to stdout via write(2) with EINTR handling.

Remove AudioPacket (dead code), --flush flag (no-op with raw write(2)).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Sources/AudioTeeCLI/AudioTee.swift

@@ -9,7 +9,6 @@ struct AudioTee {
   var stereo: Bool = false
   var sampleRate: Double?
   var chunkDuration: Double = 0.2
-  var flush: Bool = false
 
   init() {}
 
@@ -33,7 +32,6 @@ struct AudioTee {
           audiotee --include-processes 1234 5678 9012  # Tap only these processes
           audiotee --exclude-processes 1234 5678       # Tap everything except these
           audiotee --mute                       # Mute processes being tapped
-          audiotee --flush                      # Flush stdout after each chunk
         """
     )
 
@@ -45,8 +43,6 @@ struct AudioTee {
       name: "exclude-processes", help: "Process IDs to exclude (space-separated)")
     parser.addFlag(name: "mute", help: "Mute processes being tapped")
     parser.addFlag(name: "stereo", help: "Records in stereo")
-    parser.addFlag(
-      name: "flush", help: "Flush stdout after each audio chunk (reduces latency when piping)")
     parser.addOption(
       name: "sample-rate",
       help: "Target sample rate (8000, 16000, 22050, 24000, 32000, 44100, 48000)")
@@ -64,7 +60,6 @@ struct AudioTee {
       audioTee.excludeProcesses = try parser.getArrayValue("exclude-processes", as: Int32.self)
       audioTee.mute = parser.getFlag("mute")
       audioTee.stereo = parser.getFlag("stereo")
-      audioTee.flush = parser.getFlag("flush")
       audioTee.sampleRate = try parser.getOptionalValue("sample-rate", as: Double.self)
       audioTee.chunkDuration = try parser.getValue("chunk-duration", as: Double.self)
 
@@ -142,7 +137,7 @@ struct AudioTee {
       throw ExitCode.failure
     }
 
-    let outputHandler = BinaryAudioOutputHandler(flushAfterWrite: flush)
+    let outputHandler = BinaryAudioOutputHandler()
     let recorder = try AudioRecorder(
       deviceID: deviceID, outputHandler: outputHandler, convertToSampleRate: sampleRate,
       chunkDuration: chunkDuration)

Sources/AudioTeeCLI/BinaryOutputHandler.swift

@@ -4,17 +4,19 @@ import Foundation
 /// CLI-specific output handler that writes raw PCM audio to stdout
 /// and lifecycle messages to stderr via the logger.
 class BinaryAudioOutputHandler: AudioOutputHandler {
-  private let flushAfterWrite: Bool
+  private let fd = STDOUT_FILENO
 
-  init(flushAfterWrite: Bool = false) {
-    self.flushAfterWrite = flushAfterWrite
-  }
-
-  func handleAudioPacket(_ packet: AudioPacket) {
-    // Write raw binary audio data directly to stdout
-    FileHandle.standardOutput.write(packet.data)
-    if flushAfterWrite {
-      fflush(stdout)
+  func handleAudioData(_ pointer: UnsafeRawPointer, count: Int) {
+    var written = 0
+    while written < count {
+      let result = write(fd, pointer.advanced(by: written), count - written)
+      if result >= 0 {
+        written += result
+      } else if errno == EINTR {
+        continue
+      } else {
+        break  // EPIPE, EIO, etc — consumer gone or real error
+      }
     }
   }