Ψ-W1-T2: disjoint per-mode solo surfaces and a playback-gated mode switch

Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.

tests/test_footer_bar.cpp

@@ -228,6 +228,25 @@ static void testResizeSweepNoOverlap() {
     }
 }
 
+// --- Mode-segment enablement (the playback gate's visible half) ---------------
+
+static void testModeSegmentsAreLiveWithTheTransportStopped() {
+    CHECK(modeSegmentEnabled(/*isActiveSegment=*/false, /*transportRunning=*/false));
+    CHECK(modeSegmentEnabled(/*isActiveSegment=*/true, /*transportRunning=*/false));
+}
+
+static void testInactiveSegmentGoesDeadWhileTheTransportRuns() {
+    // The one that would fire a real switch — refused while playing/recording, so it
+    // must read dead rather than invite a click that silently does nothing.
+    CHECK(!modeSegmentEnabled(/*isActiveSegment=*/false, /*transportRunning=*/true));
+}
+
+static void testActiveSegmentStaysLiveWhileTheTransportRuns() {
+    // Clicking the mode you are already in is a reapply, which is never gated;
+    // dimming it would read as "this mode is unavailable".
+    CHECK(modeSegmentEnabled(/*isActiveSegment=*/true, /*transportRunning=*/true));
+}
+
 int main() {
     testWideFooterAllPlaced();
     testOffsetFooterAnchorsLeft();
@@ -241,6 +260,9 @@ int main() {
     testHitEdgesAndOutside();
     testSuppressedClaimsNothing();
     testResizeSweepNoOverlap();
+    testModeSegmentsAreLiveWithTheTransportStopped();
+    testInactiveSegmentGoesDeadWhileTheTransportRuns();
+    testActiveSegmentStaysLiveWhileTheTransportRuns();
 
     if (g_fail == 0) std::printf("footer_bar: all tests passed\n");
     else std::printf("footer_bar: %d CHECK(s) FAILED\n", g_fail);