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/actions.cpp

@@ -453,7 +453,9 @@ gaccel_register_t g_accelBankBanksFull{};
 // persists. This is an intentional divergence from persistViewState (above), which
 // DOES prompt Save-As on an unsaved project; do not "align" the two — a bank mutation
 // follows capture's quiet-persist idiom, a Design-View mutation follows the prompt idiom.
-void persistBook() { g_session->saveToActiveProject(); }
+// Returns whether a persist actually happened (false on an unsaved/no-active project),
+// so persistBankOp can skip its undo block when nothing was written.
+bool persistBook() { return g_session->saveToActiveProject(); }
 
 // Persists a completed bank index verb (create/rename/reorder/delete/evacuate/
 // move/copy) as a SINGLE batched REAPER undo point (R-B) — one bank op = one Ctrl-Z.
@@ -469,11 +471,22 @@ void persistBook() { g_session->saveToActiveProject(); }
 //
 // NO-OP GUARDRAIL: callers invoke this ONLY after the model mutation succeeded — a
 // rejected op (duplicate name, un-deletable pool, etc.) returns before reaching here,
-// so no dangling/empty undo point is ever opened.
+// so no dangling/empty undo point is ever opened for a rejected op.
+//
+// UNSAVED-PROJECT GUARDRAIL: on an unsaved / no-active project persistBook() no-ops
+// (nothing is written to ext state). We must still CLOSE the block we opened, but with
+// an EMPTY label and a zero flag so REAPER DISCARDS the point instead of recording a
+// no-effect undo entry — mirroring view.cpp's empty-plan close. The in-session model
+// change stands and persists on the user's next save; it just earns no undo point until
+// there is a project to persist into (undo of an unsaved bank op has nothing to roll
+// back to anyway). The Begin/End must still be balanced, hence the close-either-way.
 void persistBankOp(const char* label) {
     Undo_BeginBlock2(nullptr);
-    persistBook();
-    Undo_EndBlock2(nullptr, label, UNDO_STATE_MISCCFG);
+    const bool persisted = persistBook();
+    if (persisted)
+        Undo_EndBlock2(nullptr, label, UNDO_STATE_MISCCFG);
+    else
+        Undo_EndBlock2(nullptr, "", 0);  // no ext-state write -> discard the empty point
 }
 
 // Prompts the user for a single line of text via REAPER's stock input dialog.
@@ -713,11 +726,15 @@ void doBankTransferSelected(bool copy) {
             case TransferResult::RejectedSameBank: break;
         }
     }
-    // No-op guardrail: if nothing actually changed the index (every selected sample was
-    // absent, or all were pre-checked rejects), don't open an undo point. `collapsed`
-    // counts a hash-collapse — that DID mutate the index (source entry removed on a
-    // move, or dest already held the hash), so it belongs inside the undo point.
-    if (ok > 0 || collapsed > 0) {
+    // No-op guardrail — VERB-AWARE (a collapse means different things per verb):
+    //   * MOVE collapse: the source entry WAS removed (bank_book moveSample removes
+    //     unconditionally before the dest add collapses on hash), so the index DID
+    //     mutate — it counts toward opening an undo point.
+    //   * COPY collapse: the source is left intact AND the dest already held the hash,
+    //     so NOTHING changed — a true index no-op. It must NOT open an undo point.
+    // Hence: copy counts only real gains (ok); move counts gains OR collapses.
+    const bool mutated = copy ? (ok > 0) : (ok > 0 || collapsed > 0);
+    if (mutated) {
         const std::string label =
             std::string("ReaSampler: ") + verb + " sample(s)";
         persistBankOp(label.c_str());