Ψ-W2-T2: collapse a capture whose channels are bit-identical to one lossless mono channel, index value measured off the landed file

src/shell/capture/capture_realtime_finalize.cpp

@@ -184,6 +184,10 @@ CaptureResult finalizeRecording(ReaProject* proj, MediaTrack* temp,
                                                 request.endSeconds);
     }
 
+    // Channel-domain rewrite, after the frame-domain trim so it acts on the final
+    // frame set; it preserves the frame count, so the trimmed length above still holds.
+    collapseCapturedFileToMono(destPath);
+
     // Pure recorded-capture -> Sample mapping (identity, bounds echo, tier).
     RecordedCapture cap;
     cap.relativePath = paths.relativePath;
@@ -194,7 +198,9 @@ CaptureResult finalizeRecording(ReaProject* proj, MediaTrack* temp,
     cap.wetDry       = request.wetDry;
     cap.displayName  = request.baseName;
     cap.trackGuids   = request.trackGuids;
-    cap.channelCount = request.channelCount;
+    // channelCount deliberately left unset here: stampCaptureSample measures it from
+    // the file below. Echoing the request was this path's own defect — it parsed the
+    // recorded layout for the trim and still reported the requested 2.
 
     result.status  = CaptureStatus::Ok;
     result.sample  = sampleFromRecordedCapture(cap);