[Fix] (MG_Impl, PipeFill): make buffer_subdata_resident declare the live-host-writes bit - ApplyBufferWrite assigns it, so a silent content record writes false over a live write map

MobileGL/MG_Impl/Pipe/PipeFill.cpp

@@ -732,6 +732,15 @@ namespace MobileGL::MG_Pipe {
                 // store, or the pattern FillSubData expanded locally, and neither is this
                 // client's untransformed shadow of the level.
                 if (!MGPipeBuildSubDataRecord(handle, at, length, record, /*verbatimShadow=*/false)) return;
+#if MOBILEGL_BUILD_DISAGGREGATED
+                // P5 (b1): THE SECOND CONTENT EMITTER, and it has to speak for the same reason
+                // the first does. ApplyBufferWrite ASSIGNS the bit - a content record emitted
+                // while nothing maps the buffer is how the state goes back to false - so a
+                // resident sub-data that stayed silent would write false over a live write
+                // map. `glBufferSubData` against a persistently mapped arena is legal and is
+                // the ordinary Flywheel/Create shape, so that is not a corner.
+                record.HasLiveHostWrites = buffer.HasLiveHostWritesForWire() ? 1 : 0;
+#endif
                 // The application's STAGING store, valid for the duration of the call only.
                 MGPipeApplyBufferSubDataResident(record, base + (at - offset));
             });