capture: refuse the multi-track ranged item render, silence the track's children and receives for it, and gate every exact-bounds capture on its frame count

src/shell/capture/capture.cpp

@@ -32,6 +32,7 @@
 #include "core/capture/wav_codec.h"   // hashWavContent — the one WAV/RIFF owner
 #include "core/util/file_bytes.h"
 #include "core/capture/render_settings.h"
+#include "core/capture/render_window.h"  // frameCountFor — the exact-bounds number
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_EnumProjects
@@ -394,6 +395,35 @@ CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
         return result;
     }
 
+    // Exact bounds, made structural: with no tail requested the file must contain
+    // exactly the requested window's frames, so a source mode that silently widened
+    // the render fails loudly here instead of landing as a successful capture. Auto
+    // and Manual add frames by design and are skipped. UNVERIFIED: that REAPER
+    // resolves the window's two edges to frame indices the same way frameCountFor
+    // does — a DAW pass decides whether this equality is exact or off by a frame.
+    // (The file is read again by stampCaptureSample below; the duplicate read is a
+    // once-per-capture cost on an already-warm file.)
+    if (request.tailMode == TailMode::None) {
+        const WavLayout layout =
+            parseWavLayout(util::readFileBytes(expectedPath));
+        const long long expectedFrames = layout.valid
+            ? frameCountFor(request.startSeconds, request.endSeconds,
+                            static_cast<int>(layout.sampleRate))
+            : 0;
+        const long long actualFrames = static_cast<long long>(layout.frameCount());
+        if (expectedFrames > 0 && actualFrames != expectedFrames) {
+            result.status  = CaptureStatus::BoundsMismatch;
+            result.message = "Render produced " + std::to_string(actualFrames) +
+                             " frames but the requested range is " +
+                             std::to_string(expectedFrames) + " at " +
+                             std::to_string(layout.sampleRate) +
+                             " Hz -- the render did not honor the requested bounds. "
+                             "Nothing was added to the bank; the file is at: " +
+                             expectedPath;
+            return result;
+        }
+    }
+
     // Record the request's own bounds (exact) rather than re-measuring the file.
     Sample s;
     // Same uniqueTag that named the file — calling makeUniqueTag() again could