feat: switch HUD to QwenASR output once it starts producing text

In DualEngine mode, HUD initially shows Paraformer output for fast
feedback (~100ms latency). Once QwenASR produces its first text
(~2s), HUD automatically switches to QwenASR which provides better
accuracy and richer partial results (including unfixedText). This
gives users consistent preview-to-final output while maintaining
the snappy initial response.

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

Author: ZhaoChaoqun

Sources/DualEngineASR.swift

@@ -6,15 +6,18 @@ private let logger = Logger(subsystem: "com.typeless.app", category: "DualEngine
 /// 双引擎 ASR：Streaming Paraformer 实时预览 + QwenASR 流式精转写
 ///
 /// 录音过程中：
-/// - Streaming Paraformer 流式处理音频，实时输出到 HUD
+/// - 前期（~2s）：Streaming Paraformer 流式处理音频，实时输出到 HUD（低延迟预览）
 /// - QwenASR 同步接收相同音频流，持续增量推理
+/// - QwenASR 产出首段文本后，自动切换 HUD 显示源为 QwenASR（含 unfixedText）
+/// - 切换后 Paraformer 回调被忽略，但仍继续接收音频
 ///
 /// 松开 Fn 后：
 /// - QwenASR finalize 并输出最终结果（含标点）
 ///
 /// 并发模型：
 /// - `qwenQueue`（serial）：保护 QwenASR 引擎的所有调用（pushAudio / getResult / reset）
 /// - `paraformerEngine` 使用自己内部的 `recognitionQueue`，完全独立
+/// - `qwenHasOutput` 标志通过 os_unfair_lock 保护，确保跨队列安全读写
 class DualEngineASR: ASREngine {
 
     // MARK: - Constants
@@ -32,9 +35,33 @@ class DualEngineASR: ASREngine {
 
     private let qwenQueue = DispatchQueue(label: "com.typeless.dualengine.qwen", qos: .userInitiated)
 
+    // MARK: - HUD 切换状态
+
+    /// QwenASR 是否已产出文本。一旦为 true，HUD 由 QwenASR 驱动，Paraformer 回调被忽略。
+    /// 该标志只会从 false → true 单向转变（每次录音期间），在 reset()/flush() 中重置。
+    /// 被 Paraformer 的 recognitionQueue 和 qwenQueue 两个队列读写，
+    /// 使用 os_unfair_lock 保护以确保线程安全。
+    private var _qwenHasOutput = false
+    private var _qwenLock = os_unfair_lock_s()
+
     let needsPunctuation = false
     let needsITN = true
 
+    /// 线程安全读取 qwenHasOutput
+    private var qwenHasOutput: Bool {
+        get {
+            os_unfair_lock_lock(&_qwenLock)
+            let value = _qwenHasOutput
+            os_unfair_lock_unlock(&_qwenLock)
+            return value
+        }
+        set {
+            os_unfair_lock_lock(&_qwenLock)
+            _qwenHasOutput = newValue
+            os_unfair_lock_unlock(&_qwenLock)
+        }
+    }
+
     // MARK: - 初始化
 
     /// - Parameters:
@@ -50,13 +77,28 @@ class DualEngineASR: ASREngine {
     // MARK: - ASREngine 协议
 
     func processAudio(samples: [Float], onPartialResult: @escaping (String, String?) -> Void) {
-        // 1. 转发给 Paraformer 做实时预览
-        paraformerEngine.processAudio(samples: samples, onPartialResult: onPartialResult)
+        // 1. 转发给 Paraformer 做实时预览（QwenASR 接管后跳过回调）
+        paraformerEngine.processAudio(samples: samples) { [weak self] text, unfixed in
+            guard let self = self, !self.qwenHasOutput else { return }
+            onPartialResult(text, unfixed)
+        }
 
-        // 2. 同步推送给 QwenASR 流式引擎
+        // 2. 同步推送给 QwenASR 流式引擎，产出文本后接管 HUD
         qwenQueue.async { [weak self] in
             guard let self = self else { return }
             _ = self.qwenRecognizer.pushAudio(samples: samples, finalize: false)
+
+            let stableText = self.qwenRecognizer.getResult()
+            let unfixedText = self.qwenRecognizer.getUnfixed()
+
+            let hasContent = !stableText.isEmpty || (unfixedText != nil && !unfixedText!.isEmpty)
+            if hasContent {
+                if !self.qwenHasOutput {
+                    self.qwenHasOutput = true
+                    logger.info("HUD 切换：QwenASR 已产出文本，接管 HUD 显示")
+                }
+                onPartialResult(stableText, unfixedText)
+            }
         }
     }
 
@@ -75,6 +117,9 @@ class DualEngineASR: ASREngine {
             let result = self.qwenRecognizer.getResult()
             self.qwenRecognizer.reset()
 
+            // 重置 HUD 切换标志，为下一次录音做准备
+            self.qwenHasOutput = false
+
             // 同步 reset Paraformer，防止下次录音 HUD 残留上次的累积文本
             self.paraformerEngine.reset()
 
@@ -87,6 +132,7 @@ class DualEngineASR: ASREngine {
     }
 
     func reset() {
+        qwenHasOutput = false
         paraformerEngine.reset()
         qwenQueue.sync {
             qwenRecognizer.reset()