fix(dedup): hash WAV fmt+data only, skipping render-varying metadata chunks

hashWavContent walks RIFF chunks and feeds only fmt body + data payload
through FNV-1a ('W' domain-separation prefix), skipping bext/iXML/LIST that
REAPER embeds with per-render origination timestamps. Fallback to whole-file
hashBytes for non-WAV. Wired into both capture commit paths.

Legacy entries keep their stored whole-file hash; a re-capture will not
collapse onto a pre-fix entry -- a one-time clean capture resolves it.

src/capture_paths.h

@@ -15,6 +15,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <string>
+#include <vector>
 
 namespace reasampler {
 
@@ -42,6 +43,29 @@ struct BankPaths {
 // files would share, but real WAV files are never empty).
 std::string hashBytes(const std::uint8_t* data, std::size_t len);
 
+// WAV-aware content hash: hashes only the audio-defining content of a 32-bit-float
+// RIFF/WAVE file — the `fmt ` chunk body + the `data` chunk payload — skipping all
+// other RIFF chunks (e.g. `bext` origination timestamp, `iXML`, `LIST`/`INFO`, SMED).
+//
+// WHY: REAPER's offline renderer embeds render-varying metadata chunks (at minimum a
+// `bext` chunk containing the origination date/time) even when the format config blob
+// requests no BWF metadata. Two renders of identical audio therefore differ in those
+// bytes, making whole-file hashes diverge and preventing dedup collapse.
+//
+// DOMAIN SEPARATION: the FNV-1a input is prefixed with the tag byte 'W' (0x57) before
+// the fmt/data bytes are fed in, so a content hash can never equal a whole-file
+// hashBytes result for a different file of the same size.
+//
+// FALLBACK: if `bytes` does not parse as a valid RIFF/WAVE with both a `fmt ` and a
+// `data` chunk, the function falls back to whole-file hashBytes (no prefix tag) —
+// identical to calling hashBytes(bytes.data(), bytes.size()). This ensures that an
+// unrecognized or malformed file still gets a non-empty hash rather than silently
+// skipping dedup.
+//
+// Called by both capture commit paths (offline and realtime) in place of the raw
+// hashBytes call.
+std::string hashWavContent(const std::vector<std::uint8_t>& bytes);
+
 // Normalizes a path to forward slashes and strips any trailing slash. Empty in
 // -> empty out. Pure string transform (does not consult the filesystem).
 std::string normalizeSlashes(const std::string& path);