Fix drag-handoff bugs: gate FX re-resolve on outside-panel, cache unresolvable OS-drag verdict, block double FX-add retry

tests/test_instrument_drop.cpp

@@ -237,29 +237,15 @@ static void testEmbedStripIsNotHotspot() {
 // --- Drop surface parity: container vs FX button ------------------------------
 //
 // The container-drop regression (instance loads, capture does not): the two surfaces must be
-// one code path carrying one payload. The payload is a function of the capture alone, so the
-// surface cannot influence it — and both surfaces must classify as hotspots so both reach it.
-
-// Every surface a drop can land on admits the SAME capture and yields a payload that decodes
-// back to it. The payload takes the capture and nothing else, so the surface cannot influence
-// it — walking the surfaces here is what pins that the container family is not second-class.
-static void testEveryDropSurfaceCarriesTheCapture() {
-    const char* surfaces[] = {
-        "fx_chain",  // FX chain window / container list — the reported failing surface
-        "fx_0",      // floating FX window
-        "tcp.fx",    // TCP FX button — the reference path
-        "mcp.fx",    // MCP FX button
-    };
-    const std::string sampleId = "cap-7f3a";
-    for (const char* info : surfaces) {
-        CHECK(infoNamesFxHotspot(info));
-        const ParsedPreset p = parsePreset(buildInstrumentDropPreset(sampleId));
-        CHECK(p.ok);
-        CHECK(p.classId == vstClassIdHex());
-        const ComponentState cs = deserializeComponentState(p.compChunk, kRate);
-        CHECK(cs.selectionId == sampleId);
-    }
-}
+// one code path carrying one payload. buildInstrumentDropPreset takes only sampleId, so the
+// payload side of that claim is already proven once by testPresetRoundTripsThroughInstrumentReader
+// and every "fx_"/"tcp.fx"/"mcp.fx" surface classifying as a hotspot is proven by
+// testTcpMcpFxFamilyIsHotspot / testFxWindowStillHotspot. A loop that reruns both against a
+// fixed sampleId per surface string can't distinguish the surfaces (the loop body is identical
+// every iteration) — it isn't a stronger test than those two, so there is no separate test here.
+// The one thing that DOES vary by surface — the shell's TrackFX_AddByName `instantiate` value
+// picked for a container drop vs. a bare FX-button drop — lives in instrument_drop_win.cpp and
+// is untestable without a live DAW (GetThingFromPoint/TrackFX_AddByName have no pure model).
 
 // --- All-or-nothing rollback --------------------------------------------------
 
@@ -314,7 +300,6 @@ int main() {
     testNonFxSurfacesAreNotHotspot();
     testEmbedStripIsNotHotspot();
 
-    testEveryDropSurfaceCarriesTheCapture();
     testAddFailureLeavesNothingToRollBack();
     testPresetFailureRollsBackTheCreatedIndex();
     testSuccessKeepsTheInstance();