Ψ-W2-T2 remediation: atomic temp+rename collapse write, honest unknown-channel fallback, [verify — DAW] markers, corrected+filed bake-collapse deferral, observable collapse message, quiet-NaN test

tests/test_wav_codec.cpp

@@ -51,6 +51,16 @@ static void putFloat(std::vector<std::uint8_t>& b, float f) {
     std::memcpy(tmp, &f, 4);
     for (int i = 0; i < 4; ++i) b.push_back(tmp[i]);
 }
+static float floatFromBits(std::uint32_t bits) {
+    float f;
+    std::memcpy(&f, &bits, 4);
+    return f;
+}
+static std::uint32_t bitsFromFloat(float f) {
+    std::uint32_t bits;
+    std::memcpy(&bits, &f, 4);
+    return bits;
+}
 
 // A canonical 32-bit-float WAV: RIFF/WAVE, fmt (tag 3, 16-byte body), data holding
 // `frames` interleaved frames of `channels`. `leadingJunk` optionally inserts an
@@ -746,6 +756,25 @@ static void testCollapseChangesContentHash() {
     CHECK(hashWavContent(c.bytes) != hashWavContent(wav));
 }
 
+// The float->double->float rebuild's stated hole is a SIGNALING NaN (double promotion
+// quiets it); a QUIET NaN is not that hole. Both channels carry the identical
+// quiet-NaN bit pattern, so the predicate collapses; the rebuilt mono channel must
+// carry that exact bit pattern back, not merely "some NaN".
+static void testCollapsePreservesQuietNaNBitPattern() {
+    constexpr std::uint32_t kQuietNaNBits = 0x7FC12345u;  // exponent all-ones, mantissa MSB set
+    auto wav = buildFloatWav(2, 48000, 1,
+                             [kQuietNaNBits](std::size_t, std::uint16_t) {
+                                 return floatFromBits(kQuietNaNBits);
+                             });
+    const MonoCollapse c = collapseToMono(wav);
+    CHECK(c.collapsed);
+    const WavLayout L = parseWavLayout(c.bytes);
+    CHECK(L.valid && L.channelCount == 1 && L.frameCount() == 1);
+    const auto pcm = extractFloatFrames(c.bytes, L, 0, 1);
+    CHECK(pcm.size() == 1);
+    if (!pcm.empty()) CHECK(bitsFromFloat(pcm[0]) == kQuietNaNBits);
+}
+
 int main() {
     testParseCanonicalStereo();
     testParseMonoAndLeadingChunk();
@@ -780,6 +809,7 @@ int main() {
     testCollapseThroughOddPaddedLeadingChunk();
     testCollapseDeclinesOnUnparseableBytes();
     testCollapseChangesContentHash();
+    testCollapsePreservesQuietNaNBitPattern();
 
     if (g_fail == 0) std::printf("wav_codec: all tests passed\n");
     else             std::printf("wav_codec: %d CHECK(s) FAILED\n", g_fail);