Phases 2-6: detection, visual timeline, backend hand-off, voiceprints

Phase 2 (call detection): CallDetector using CoreAudio per-process mic
attribution (anarlog technique) — robust start+stop for Zoom/Teams/Signal/Meet,
ignoring our own recording; auto-record toggle. Built; pending live multi-app
confirmation by the user.

Phase 3 (visual timeline foundation): AppAdapter protocol + SpeakerObservation,
TimelineBuilder (hysteresis/overlap/self-merge/aliases), VisualTimeline (schema
1.1), TextRecognizer (Vision OCR), FrameSampler + GridCallAnalyzer (name OCR +
saturated-highlight active-speaker attribution), SignalAdapter, VisualObserver
(window capture; frames released, never saved; minimized->visual_gap, idle != gap).
Synthetic-frame tested; adapter geometry pending real Signal fixtures + live
VisualObserver validation.

Phase 5 (backend hand-off): SparkControlClient (multipart label-merge, sequential,
TLS-skip, 503 Retry-After/413), SessionPackager (chunk plan + WAV slice + timeline
slice/rebase), TranscriptAssembler + SpeakersFile, TranscriptPipeline. Validated
END-TO-END against the live backend (chunk -> label-merge -> speakers.json).

Phase 6 (voiceprints): VoiceprintStore (known_voiceprints, persist named
fingerprints, skip Unknown). Wired: 'Send to backend' button + transcript status,
auto-send toggle (default off) + self-name setting.

All adversarial-review findings fixed. App + XCTest suite build; tests pass.

Ten31Transcripts/Audio/Resampler.swift

@@ -24,7 +24,12 @@ final class Resampler {
         guard !ended, input.frameLength > 0 else { return nil }
 
         if converter == nil || sourceFormat != input.format {
-            converter = AVAudioConverter(from: input.format, to: Self.targetFormat)
+            let c = AVAudioConverter(from: input.format, to: Self.targetFormat)
+            // Highest-quality sample-rate conversion: best anti-aliasing on the
+            // 48k→16k downsample, which avoids harsh artifacts on loud/bright speech.
+            c?.sampleRateConverterQuality = .max
+            c?.sampleRateConverterAlgorithm = AVSampleRateConverterAlgorithm_Mastering
+            converter = c
             sourceFormat = input.format
         }
         guard let converter else { return nil }