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

src/core/capture/wav_codec.h

@@ -113,7 +113,8 @@ struct MonoCollapse {
 // The rebuild is a canonical minimal WAV, so non-audio chunks (a renderer's `bext`
 // timestamp, iXML, LIST) do not survive it. That much hashWavContent already skips —
 // but the collapse rewrites the `fmt ` body and the `data` payload too, which moves
-// the file's content identity; see this directory's CLAUDE.md for what that costs.
+// the file's content identity; see this directory's CLAUDE.md for what that costs,
+// including the bext/source-position consequence beyond hashing.
 MonoCollapse collapseToMono(const std::vector<std::uint8_t>& bytes);
 
 // --- Content identity (dedup hashes) -----------------------------------------