feat(view): D4 Design View action family + reapply-on-open wiring

Register toggle/activate/tag/untag/show-both actions driving the D2
shell and D3 model; reapply saved active mode on project load via a
persist load-signal seam. Shared guidString helper; pure nextModeId
unit-tested.

src/main.cpp

@@ -20,10 +20,12 @@
 
 #include <string>
 
+#include "actions.h"
 #include "bank_model.h"
 #include "bank_panel.h"
 #include "capture.h"
 #include "persist.h"
+#include "view.h"
 
 // Persistent action-id prefix for the ReaSampler action family.
 // Every bindable action (capture / insert / slot / verify) mints its command id
@@ -63,6 +65,18 @@ static reasampler::ReaSamplerSession g_session;
 static void OnTimer()
 {
     g_session.poll();
+
+    // D4 reapply-on-open glue. persist stays MODEL-ONLY (it loads the saved view
+    // model but deliberately does NOT apply visibility — that would couple persist
+    // to the view shell). Instead poll() raises a one-shot load signal; here — the
+    // integration layer that already drives both persist and the view shell — we
+    // drain it and reapply the SAVED active mode's visibility/processing so opening a
+    // project saved in Design mode parks the Arrange tracks automatically, no manual
+    // toggle. Fires exactly once per load (consumeLoadSignal clears it); idle ticks
+    // skip it. proj = nullptr -> REAPER's active project (the one poll just loaded).
+    if (g_session.consumeLoadSignal())
+        reasampler::applyMode(g_session.view(), g_session.view().activeModeId(), nullptr);
+
     // Reflect a live bank change (capture / project load) in the docked grid.
     // Cheap when the bank is unchanged (a fingerprint compare); repaints only on
     // an actual change. No-op when the panel is closed.
@@ -118,6 +132,9 @@ static bool OnHookCommand(int command, int /*flag*/)
     if (command == 0) return false;
     if (command == g_cmdCaptureMasterSpike) { RunCaptureMasterSpike(); return true; }
     if (command == g_cmdToggleBankPanel)    { reasampler::bankPanelToggle(); return true; }
+    // Design View action family (D4). Claims only its own ids; returns false for the
+    // rest so this hook keeps looking (per the contract).
+    if (reasampler::designViewHandleCommand(command)) return true;
     return false;
 }
 
@@ -146,6 +163,9 @@ extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
             g_rec->Register("-timer", (void*)&OnTimer);
             g_rec->Register("-toggleaction", (void*)&OnToggleAction);
             g_rec->Register("-hookcommand", (void*)&OnHookCommand);
+            // Tear down the Design View action family (D4) — mirror-unregisters each
+            // gaccel + command_id with '-'-prefixed strings. After the hook is gone.
+            reasampler::designViewUnregisterActions(g_rec);
             g_rec->Register("-gaccel", (void*)&g_accelToggleBankPanel);
             g_rec->Register("-command_id",
                             (void*)(REASAMPLER_ACTION_PREFIX "TOGGLE_BANK_PANEL"));
@@ -201,8 +221,14 @@ extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
         rec->Register("toggleaction", (void*)&OnToggleAction);
     }
 
-    // One hookcommand routes every ReaSampler action (spike + toggle). Registered
-    // once, after both command ids are minted.
+    // Register the Design View action family (D4): toggle/activate mode, tag/untag/
+    // show-both selected tracks. Each mints its own command_id + gaccel; the single
+    // hookcommand below routes them via designViewHandleCommand. Registered before
+    // the hook so every id is minted first.
+    reasampler::designViewRegisterActions(rec, &g_session);
+
+    // One hookcommand routes every ReaSampler action (spike + toggle + Design View).
+    // Registered once, after all command ids are minted.
     rec->Register("hookcommand", (void*)&OnHookCommand);
 
     // Drive project-load / Save-As detection (M4 persist). The timer polls the