Q-W1 pt2: core/shell/app relocation + sub-namespaces; one concrete ui::Rect (LTRB fork retired); slot_map split from bank_book; BankIndex→BankModel; 59/59 green

src/core/ui/mode_enable.cpp

@@ -0,0 +1,21 @@
+// mode_enable — pure implementation. See mode_enable.h. NO REAPER / SWELL / LICE / vendor.
+
+#include "core/ui/mode_enable.h"
+
+#include "core/view/view_mode_model.h"  // kArrangeModeId / kDesignModeId — the ONE home for the mode ids
+
+namespace reasampler::ui {
+
+bool tagButtonEnabled(const std::string& activeModeId, TagTarget target) {
+    // The target's own mode id, so the rule is a single "target != active" compare.
+    const char* targetId =
+        (target == TagTarget::Arrange) ? kArrangeModeId : kDesignModeId;
+
+    // Fail-open on an unrecognized active id (neither seed mode): every button live, so a
+    // future added mode never dead-locks the bar and the user can always reach the action.
+    if (activeModeId != kArrangeModeId && activeModeId != kDesignModeId) return true;
+
+    return activeModeId != targetId;
+}
+
+} // namespace reasampler::ui