fix(persist): use project-object identity to stop forked-bank cross-contamination

M4's GUID-only classifier read a tab-switch between two Save-As forks (shared
copied GUID, different paths) as a Save-As and clobbered a bank. Thread
sameProjectObject into classifyProjectTransition: a different object always
Loads, never relocates; a forked sibling gets re-GUID'd to diverge.

src/persist.h

@@ -48,15 +48,18 @@ inline constexpr const char* kProjExtGuidKey = "project_guid";
 // Owns the session's BankIndex and drives persistence against the active REAPER
 // project. One instance lives for the extension's lifetime (main.cpp). It tracks
 // the project identity it last saw so the timer tick can detect a project load
-// (identity changed) and a Save-As (same project, path changed) and react:
+// (a different project became active) and a Save-As (SAME project, path changed):
 //
 //   * project load       -> load the index from ext state, resolve bank paths
 //   * Save-As (new dir)   -> relocate the bank folder under the new .rpp
 //
-// Identity is CONTENT-BASED, not pointer-based: persist keys Load/Save-As off a
-// GUID it mints and stores in each project's ext state, not the ReaProject*
-// pointer (REAPER recycles pointer addresses across close/open, which let a
-// project switch masquerade as a Save-As and clobber a bank — the M4 defect).
+// Identity rests on the live ReaProject* pointer FIRST (a genuine Save-As is one
+// object saved to a new path — same pointer; a tab-switch/open is a different
+// object), with a minted GUID as a SECONDARY signal to survive pointer *reuse*
+// (REAPER recycles a closed project's address). The pointer is what distinguishes
+// a Save-As from a switch between two FORKED siblings that share a copied GUID on
+// disk (the W10 data-integrity defect: dropping the pointer let a fork tab-switch
+// masquerade as a Save-As and clobber a bank).
 //
 // The bank itself is exposed for the capture/action layer to mutate; persist
 // only reads it on save and replaces it on load.
@@ -95,12 +98,15 @@ private:
     ViewModeModel view_;
 
     // The project identity last observed by poll(), used to detect load/Save-As.
-    // Identity is the GUID we mint per project (kProjExtGuidKey), NOT the raw
-    // ReaProject* pointer — see the class comment for why. The .rpp path is
-    // tracked alongside so a same-GUID path change (Save-As) is distinguishable
-    // from a same-GUID same-path idle tick (Save in place / no change).
+    // The pointer is the PRIMARY signal (same object across ticks = a candidate
+    // Save-As; different object = a switch/open, never a relocate). The GUID and
+    // path travel alongside: the GUID distinguishes pointer *reuse* and drives
+    // forked-sibling re-divergence; the path tells a Save-As from an idle tick.
+    // Held as void* so the header stays REAPER-free; it is a compared-only opaque
+    // handle (never dereferenced), so a stale/recycled address is harmless.
+    void*       lastProject_ = nullptr;   // last active ReaProject* (opaque; compare only)
     std::string lastGuid_;                // "" until the first saved project is seen
-    std::string lastRppPath_;             // .rpp path last seen for lastGuid_
+    std::string lastRppPath_;             // .rpp path last seen for lastProject_
     bool        primed_ = false;          // false until the first poll() observes state
 
     // Load the index from the given project's ext state and resolve bank paths