Throttle new-content enumeration to 500ms, off the 30/s OnTimer tick

src/shell/panel/panel_input.cpp

@@ -135,8 +135,9 @@ void enumerateLiveGuids(ReaProject* proj, std::set<std::string>& allGuids,
 }
 
 // One detection tick: REAPER exposes no "item/track added" callback, so this diffs live
-// GUIDs against the baseline and auto-tags the new ones into the active mode. Runs every
-// timer tick regardless of panel open/close. READ-ONLY on the project; mutates only the
+// GUIDs against the baseline and auto-tags the new ones into the active mode. Called every
+// timer tick regardless of panel open/close, but the enumeration itself is throttled to
+// kDetectIntervalMs (see the gate below). READ-ONLY on the project; mutates only the
 // in-memory membership index — deliberately OUTSIDE any Undo block (auto-tag is a
 // background metadata update, not a destructive edit; an Undo block here would flood
 // REAPER's history with an entry per tick that sees new content).
@@ -146,6 +147,14 @@ void enumerateLiveGuids(ReaProject* proj, std::set<std::string>& allGuids,
 bool detectNewContent() {
     if (!g_panel.session) return false;
 
+    // Throttles the enumeration (O(T+I) REAPER calls + allocations) to kDetectIntervalMs,
+    // independent of how often the caller ticks. A skipped tick leaves reloadPending/the
+    // baseline untouched, so the guards below still run before the NEXT diff whenever this
+    // gate next opens — only the diff's cadence changes, not its correctness.
+    const unsigned int now = GetTickCount();
+    if (now - g_panel.lastDetectTick < kDetectIntervalMs) return false;
+    g_panel.lastDetectTick = now;
+
     ReaProject* proj = EnumProjects(-1, nullptr, 0);
 
     // A project (re)load re-arms the first-poll guard so we never diff across two
@@ -538,17 +547,19 @@ void unregisterAccel() {
 namespace reasampler {
 
 void bankPanelNotifyProjectLoaded() {
-    // Arms the new-content detector to re-baseline on its next tick so the just-loaded
-    // project's pre-existing content is the baseline (nothing new) rather than diffed
-    // against the previous project and mass-tagged. A flag, not an inline reset, because
-    // detectNewContent owns the baseline and runs later in the SAME OnTimer tick.
+    // Arms the new-content detector to re-baseline on its next ENUMERATING tick (the flag
+    // persists across any throttled/skipped ticks in between) so the just-loaded project's
+    // pre-existing content is the baseline (nothing new) rather than diffed against the
+    // previous project and mass-tagged. A flag, not an inline reset, because detectNewContent
+    // owns the baseline and drains this before its own diff.
     panel::g_panel.reloadPending = true;
 }
 
 void bankPanelRefresh() {
-    // New-content auto-tag detection runs EVERY tick regardless of panel open/close:
-    // tracks/items are created in the arrange view, not the panel. READ-ONLY on the
-    // project; only mutates the in-memory membership index.
+    // New-content auto-tag detection is CALLED every tick regardless of panel open/close
+    // (tracks/items are created in the arrange view, not the panel), but the enumeration
+    // it drives is throttled — see kDetectIntervalMs. READ-ONLY on the project; only
+    // mutates the in-memory membership index.
     const bool tagged = panel::detectNewContent();
 
     // Lane minting runs ONLY when detection just tagged new content — a track can only

src/shell/panel/panel_state.h

@@ -206,6 +206,13 @@ inline constexpr unsigned int kTooltipDelayMs = 500;
 inline constexpr int kTooltipCharPx = 7;
 inline constexpr int kTooltipTextH  = 14;
 
+// New-content detection's enumeration cadence — matches the VST3 side's own
+// kSyncTimerIntervalMs (editor_platform.cpp), this codebase's established interval for a
+// background poll nothing visible depends on. Auto-tag is an invisible metadata update
+// (see detectNewContent), so a 15x cadence cut (30/s -> 2/s) costs latency no one watches
+// for, not correctness.
+inline constexpr unsigned int kDetectIntervalMs = 500;
+
 // Client area top to bottom: top toolbar | split body | bottom toolbar | footer.
 // 26, not 24: Font::RegionTitle's line box (19px em + Segoe UI's leading) is ~25px, and
 // DT_VCENTER clips to the rect.
@@ -345,12 +352,18 @@ struct PanelState {
     bool previewActive = false;
     bool previewInited = false;  // guards double init / deinit
 
-    // Each timer tick diffs the live track+item GUID set against the previous tick to
-    // auto-tag new content. GuidBaseline self-arms on first observe() so pre-existing
-    // content is never mass-tagged. Project-load re-arm is driven by persist's load
-    // signal, not a ReaProject* compare — a recycled address previously mis-tagged tracks.
+    // Each enumerating tick (kDetectIntervalMs-throttled) diffs the live track+item GUID
+    // set against the prior enumeration to auto-tag new content. GuidBaseline self-arms on
+    // first observe() so pre-existing content is never mass-tagged. Project-load re-arm is
+    // driven by persist's load signal, not a ReaProject* compare — a recycled address
+    // previously mis-tagged tracks.
     GuidBaseline contentBaseline;
     bool         reloadPending = false;  // set by bankPanelNotifyProjectLoaded; drained next detect tick
+
+    // Throttles enumerateLiveGuids to kDetectIntervalMs regardless of how often
+    // bankPanelRefresh itself is called (the OnTimer poll, ~30/s, plus a handful of
+    // post-capture/ingest/bake call sites). 0 forces the very first tick through.
+    unsigned int lastDetectTick = 0;
 };
 
 // Defined in panel_window.cpp (the lifecycle owner).