Merge Θ-W1-T2: fix drag-out audio loss and FX-container drops, re-home ingest

tests/test_instrument_drop.cpp

@@ -235,6 +235,50 @@ static void testEmbedStripIsNotHotspot() {
     CHECK(!infoNamesFxHotspot("mcp.fxembed extra"));
 }
 
+// Do not reintroduce a per-surface "capture carries" loop test: buildInstrumentDropPreset takes
+// only sampleId (proven by testPresetRoundTripsThroughInstrumentReader), and per-surface hotspot
+// coverage already exists (testTcpMcpFxFamilyIsHotspot / testFxWindowStillHotspot) — a loop with
+// an identical body per surface string can't distinguish them.
+
+// --- All-or-nothing rollback --------------------------------------------------
+
+// The add failed: nothing was created, so there is nothing to delete and nothing loaded.
+static void testAddFailureLeavesNothingToRollBack() {
+    const DropOutcome out = decideDropOutcome(DropAttempt{-1, false});
+    CHECK(!out.loaded);
+    CHECK(out.rollbackFxIndex < 0);
+}
+
+// The instance was created but the preset did not apply: the caller MUST delete that exact
+// index — an instance without its capture is the orphan the contract forbids.
+static void testPresetFailureRollsBackTheCreatedIndex() {
+    const DropOutcome zero = decideDropOutcome(DropAttempt{0, false});
+    CHECK(!zero.loaded);
+    CHECK(zero.rollbackFxIndex == 0);
+    const DropOutcome later = decideDropOutcome(DropAttempt{4, false});
+    CHECK(!later.loaded);
+    CHECK(later.rollbackFxIndex == 4);
+    // Container-addressed indices (0x2000000-flagged) roll back by the same rule — the
+    // obligation follows the index REAPER handed back, whatever space it names.
+    const DropOutcome inContainer = decideDropOutcome(DropAttempt{0x2000000 + 5, false});
+    CHECK(!inContainer.loaded);
+    CHECK(inContainer.rollbackFxIndex == 0x2000000 + 5);
+}
+
+// Both halves succeeded: loaded, and nothing to undo.
+static void testSuccessKeepsTheInstance() {
+    const DropOutcome out = decideDropOutcome(DropAttempt{2, true});
+    CHECK(out.loaded);
+    CHECK(out.rollbackFxIndex < 0);
+}
+
+// A "preset applied" report with no instance behind it can never read as loaded.
+static void testNoInstanceIsNeverLoaded() {
+    const DropOutcome out = decideDropOutcome(DropAttempt{-1, true});
+    CHECK(!out.loaded);
+    CHECK(out.rollbackFxIndex < 0);
+}
+
 int main() {
     testClassIdHexPinnedPerChannel();
     testPresetRoundTripsThroughInstrumentReader();
@@ -249,6 +293,11 @@ int main() {
     testNonFxSurfacesAreNotHotspot();
     testEmbedStripIsNotHotspot();
 
+    testAddFailureLeavesNothingToRollBack();
+    testPresetFailureRollsBackTheCreatedIndex();
+    testSuccessKeepsTheInstance();
+    testNoInstanceIsNeverLoaded();
+
     if (g_fail == 0) std::printf("All tests passed.\n");
     return g_fail ? 1 : 0;
 }