Preserve Sortformer tentative tail during finalize

Sources/FluidAudio/Diarizer/Sortformer/SortformerDiarizerPipeline.swift

@@ -501,7 +501,9 @@ public final class SortformerDiarizer: Diarizer {
             }
 
             var lastResult: DiarizerChunkResult?
+            var tentativeToFlush = _timeline.numTentativeFrames
             if let chunk = try makeStreamingChunkLocked() {
+                tentativeToFlush = chunk.tentativeFrameCount
                 let finalizedChunk = DiarizerChunkResult(
                     startFrame: chunk.startFrame,
                     finalizedPredictions: chunk.finalizedPredictions,
@@ -514,7 +516,7 @@ public final class SortformerDiarizer: Diarizer {
                 lastResult = finalizedChunk
             }
 
-            let targetEndFrame = _numFramesProcessed + min(_timeline.numTentativeFrames, config.chunkLen)
+            let targetEndFrame = _numFramesProcessed + min(tentativeToFlush, config.chunkLen)
             let exactPaddingSamples = exactFinalizationPaddingSamples(targetEndFrame: targetEndFrame)
             if exactPaddingSamples > 0 {
                 audioBuffer.append(contentsOf: [Float](repeating: 0, count: exactPaddingSamples))

Tests/FluidAudioTests/Diarizer/Sortformer/SortformerStreamingIntegrationTests.swift

@@ -44,4 +44,35 @@ final class SortformerStreamingIntegrationTests: XCTestCase {
         XCTAssertEqual(finalChunk?.tentativePredictions.count, 0)
         XCTAssertEqual(streamingDiarizer.timeline.numTentativeFrames, 0)
     }
+
+    func testFinalizeSessionFlushesTentativeTailAfterAddAudioOnly() async throws {
+        let config = SortformerConfig.default
+        let models: SortformerModels
+        do {
+            models = try await loadModelsForTest(config: config)
+        } catch {
+            throw XCTSkip("Sortformer models unavailable in this environment: \(error)")
+        }
+        let samples = try DiarizationTestFixtures.fixtureAudio(sampleRate: config.sampleRate, limitSeconds: 4.0)
+
+        let bufferedDiarizer = SortformerDiarizer(config: config)
+        bufferedDiarizer.initialize(models: models)
+        bufferedDiarizer.addAudio(samples)
+        let bufferedFinalChunk = try bufferedDiarizer.finalizeSession()
+
+        let streamingDiarizer = SortformerDiarizer(config: config)
+        streamingDiarizer.initialize(models: models)
+        for chunk in DiarizationTestFixtures.chunk(samples, sizes: [4_800, 7_680, 9_600]) {
+            let _ = try streamingDiarizer.process(samples: chunk)
+        }
+        let _ = try streamingDiarizer.finalizeSession()
+
+        XCTAssertNotNil(bufferedFinalChunk)
+        XCTAssertEqual(bufferedFinalChunk?.tentativeFrameCount, 0)
+        XCTAssertEqual(bufferedDiarizer.timeline.numTentativeFrames, 0)
+        XCTAssertEqual(
+            bufferedDiarizer.timeline.numFinalizedFrames,
+            streamingDiarizer.timeline.numFinalizedFrames
+        )
+    }
 }