Buffer undo trace to a ring, add dump action, stop per-tick loadSaveProj spam

Trace lines fill a 4096-line ring instead of hitting the console per line;
DUMP_UNDO_TRACE drains it in one ShowConsoleMsg call. Overflow is marked, not silent.

src/app/main.cpp

@@ -108,6 +108,9 @@ static void RunShowVersion(int) {
     // the console window).
     ShowConsoleMsg(("ReaSampler " + reasampler::version::appVersion() + "\n").c_str());
 }
+// TEMPORARY: drains the undo-trace ring buffer to the console in one call. See
+// undo_trace.h; revert together with the rest of the undo-span tracing pass.
+static void RunDumpUndoTrace(int) { reasampler::undoTraceDump(); }
 
 // ONE row per bindable action this TU owns: FOREVER-STABLE id suffix, Actions-list
 // phrase, handler, per-row arg. Registration, hookcommand dispatch, and the unload
@@ -170,6 +173,9 @@ static std::vector<reasampler::ActionTableRow> buildMainActionTable() {
     rows.push_back({"IMPORT_BANK_PACKAGE", "import bank package (.rsbank)",
                     &RunImportBankPackage});
     rows.push_back({"SHOW_VERSION", "show version", &RunShowVersion});
+    // TEMPORARY: see undo_trace.h; revert together with the rest of the undo-span
+    // tracing pass.
+    rows.push_back({"DUMP_UNDO_TRACE", "DIAG: dump undo trace", &RunDumpUndoTrace});
 
     return rows;
 }
@@ -185,10 +191,15 @@ static void OnTimer()
     if (capture::g_rtCapture) capture::DriveRealtimeCapture(g_session);
 
     // TEMPORARY: captured in a local (rather than calling GetCurrentProjectInLoadSave()
-    // twice) so the trace can report the value on every tick, standoff or not, with no
-    // change to the call below. See undo_trace.h.
+    // twice) so the trace can report it without a second call, with no change to the
+    // call below. See undo_trace.h. Traced only on CHANGE — every tick reads this
+    // regardless of state, and the transition is the whole point of the line.
     ReaProject* const loadSaveProj = GetCurrentProjectInLoadSave();
-    REASAMPLER_TRACE("[Timer] loadSaveProj=%p", (void*)loadSaveProj);
+    static ReaProject* s_tracedLoadSaveProj = nullptr;
+    if (loadSaveProj != s_tracedLoadSaveProj) {
+        REASAMPLER_TRACE("[Timer] loadSaveProj=%p", (void*)loadSaveProj);
+        s_tracedLoadSaveProj = loadSaveProj;
+    }
 
     // A project load or save is IN FLIGHT, so this tick is running inside its own message
     // pump — a restore brings plugins online and a plugin load pumps. Everything below