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/CLAUDE.md

@@ -89,6 +89,14 @@ Detail specific to these pure modules:
   which is what the bit-identical-repeats invariant actually asks for. Do not "fix"
   this by hashing pre-collapse — that would make two entries with different audio
   layouts share one identity.
+- **The collapse's minimal rebuild also drops `bext`/iXML/LIST — a source-position
+  consequence, not only a hashing one.** REAPER's renderer writes a `bext` time
+  reference, and REAPER's own import paths can position an item at that BWF timestamp,
+  so a collapsed capture loses it while a declined (non-collapsed) capture from the same
+  action keeps it — two captures from one action behave differently on re-import.
+  `shell/capture/insert.cpp` is unaffected (it drives `SetEditCurPos` + `InsertMedia`
+  rather than reading BWF), so this is not a defect in the shipped insert path.
+  Accepted, not verified against a DAW re-import: `[verify — DAW]`.
 - `tail_control`'s `kDefaultManualTailMs`/`kManualStepMs` and
   `render_settings`'s `kMaxTailMs`/`kAutoTrimThresholdDb` are separate constants
   in separate files by design (panel-facing default/step vs. runaway-guard cap)

src/core/capture/wav_codec.cpp

@@ -284,8 +284,13 @@ MonoCollapse collapseToMono(const std::vector<std::uint8_t>& bytes) {
         }
     }
 
-    // float -> double -> float round-trips exactly (double represents every float),
-    // so channel 0 reaches the rebuilt file unaltered.
+    // float -> double -> float round-trips exactly for every finite value and for
+    // +-0/+-infinity (double represents every float bit pattern in those classes), so
+    // channel 0 reaches the rebuilt file unaltered. The one hole: a signaling NaN is
+    // quieted by the float->double promotion, so an identical-bit sNaN pair could
+    // collapse to a different bit pattern than it started with. Not reachable from
+    // REAPER-rendered audio, but the bit-identical predicate above admits NaN inputs,
+    // so this rebuild is not exempt from the claim it makes.
     std::vector<double> mono(frames);
     for (std::size_t f = 0; f < frames; ++f)
         mono[f] = static_cast<double>(pcm[f * stride]);

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) -----------------------------------------