fix(m10): item-scope take-FX fingerprint; Windows path case-fold; comments

Item scope now reads the active take's FX chain via TakeFX_* (new
fxChainIdentityForItems helper), not the owning track's chain.
normalizeSlashes lowercases on _WIN32 for detectParent. Stale
comments corrected; case-fold tests added.

src/provenance_shell.h

@@ -22,20 +22,26 @@
 #include "provenance.h"
 
 class MediaTrack;
+class MediaItem;
 
 namespace reasampler {
 
 class BankBook;
 
-// The in-scope FX-chain identity of a source track, folded to the pure
-// provenance string. For TRACK scope this is the track's own FX chain; for ITEM
-// scope the take/item FX are the in-scope chain — but item/take FX are not
-// enumerable via the TrackFX_* family, so an item-scope capture folds an EMPTY
-// chain identity (the drift signal then keys on scope + range only, which is
-// honest: we do not claim to fingerprint take FX we cannot read). TRACK scope reads
-// TrackFX_GetCount / GetFXName / GetFXGUID / GetEnabled in chain order.
+// The in-scope FX-chain identity of a source track (Track scope), folded to the
+// pure provenance string. Reads the track's own FX chain via TrackFX_GetCount /
+// TrackFX_GetFXName / TrackFX_GetFXGUID / TrackFX_GetEnabled in chain order.
 std::string fxChainIdentityForTrack(MediaTrack* tr);
 
+// The in-scope FX-chain identity for Item scope: enumerates each item's active
+// take FX chain via TakeFX_GetCount / TakeFX_GetFXName / TakeFX_GetFXGUID /
+// TakeFX_GetEnabled, in item order then FX order, combined with
+// combineChainIdentities so distinct per-item partitions never collide. Returns
+// the combined identity string (empty combined identity for a no-FX or no-item
+// set). The items vector is the same source-item set the shell collected for the
+// item-scope capture (selected items whose owning tracks were also collected).
+std::string fxChainIdentityForItems(const std::vector<MediaItem*>& items);
+
 // Reads the media-file path of every SELECTED media item's active take source
 // (GetMediaItemTake_Source -> GetMediaSourceFileName), normalized to forward-slash.
 // Unresolvable items (no take / no source / empty name) are omitted — never an