feat(persist): reload book+view on undo/redo via projectconfig hook (R-B)

BeginLoadProjectState(isUndo) requests a deferred reload the timer drains
next tick, once REAPER has restored ext-state. Hook owns undo/redo; identity
poll still owns open/tab-switch/save-as. Fixes copy-collapse over-count
(verb-aware guard) and dangling undo point on unsaved-project bank ops.

src/persist.h

@@ -126,13 +126,35 @@ public:
     // to the active project's ext state (namespace "reasampler"), and clear the retired
     // legacy `bank_index` key. Non-destructive beyond writing our own ext-state keys.
     // Safe to call when there is no active/saved project (it no-ops).
-    void saveToActiveProject();
+    //
+    // Returns true iff a persist actually happened (an active, SAVED project existed);
+    // false when it no-op'd (no active project, or an unsaved one with no .rpp). Lets a
+    // caller wrapping this in an undo block skip the block when nothing was written, so
+    // no dangling no-effect undo entry is opened on an unsaved project.
+    bool saveToActiveProject();
 
     // Poll the active project. Detects a project load (active project changed)
     // and a Save-As (active project's .rpp path changed) and reacts accordingly.
     // Intended to be driven by REAPER's "timer" register. Idempotent per tick.
+    //
+    // Also drains a pending undo/redo reload (requestReload): a Ctrl-Z / Ctrl-Shift-Z
+    // keeps the SAME project identity (same ReaProject*/GUID/.rpp path), so the
+    // identity classifier below reads it as NoOp and would never re-read ext state.
+    // The projectconfig hook (main.cpp) raises the reload flag on an undo/redo state
+    // restore; poll() honours it FIRST — reloading book_ + view_ + tail_ from the
+    // (now-restored) ext state of the current project — before the identity check, so
+    // the undo is reflected in-session without any content polling.
     void poll();
 
+    // Request a reload of book_ + view_ + tail_ from the CURRENT active project's ext
+    // state on the next poll() tick. Raised by the projectconfig hook (main.cpp) ONLY
+    // on an undo/redo state restore (isUndo). Deferred (a flag, not an immediate read)
+    // because the projectconfig callback fires BEFORE REAPER has restored the project's
+    // <EXTSTATE> block — reading GetProjExtState synchronously there would return the
+    // PRE-undo value. Draining it on the next timer tick reads the restored value. This
+    // is REAPER-facing shell state; the request itself carries no REAPER types.
+    void requestReload();
+
     // Load signal for the D4 reapply-on-open glue. poll() raises this whenever it
     // (re)loads the view model from a project — prime, a project switch/open, or a
     // forked-sibling load. consumeLoadSignal() returns true ONCE per load and clears
@@ -171,6 +193,7 @@ private:
     std::string lastRppPath_;             // .rpp path last seen for lastProject_
     bool        primed_ = false;          // false until the first poll() observes state
     bool        loadPending_ = false;     // raised by loadFromProject; drained by consumeLoadSignal
+    bool        reloadRequested_ = false; // raised by requestReload (projectconfig undo/redo); drained by poll
 
     // Load the book from the given project's ext state (the `banks` key, else the
     // legacy `bank_index` key migrated into the pool) and resolve bank paths against