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

tests/test_bank_model.cpp

@@ -573,8 +573,26 @@ static void testSeamFieldsAdditiveInvariant() {
     CHECK(idx.query("id-z")->rootNote == 60);  // move did not disturb seam fields
 }
 
+// A collapsed capture is a 1-channel entry, and the JSON is the only thing carrying
+// that count across a project reload — the instrument's mono/stereo default reads it.
+static void testMonoChannelCountRoundTrip() {
+    BankModel idx;
+    Sample s = fullSample("mono");
+    s.channelCount = 1;
+    CHECK(idx.add(s) == AddResult::Added);
+
+    const std::string json = idx.serialize();
+    CHECK(json.find("\"channelCount\":1") != std::string::npos);
+
+    auto back = BankModel::deserialize(json);
+    CHECK(back.has_value());
+    CHECK(back && back->query("id-mono") &&
+          back->query("id-mono")->channelCount == 1);
+}
+
 int main() {
     testFullFieldRoundTrip();
+    testMonoChannelCountRoundTrip();
     testSerializeGoldenLiteral();
     testDedupByHash();
     testTierFilterAndMove();