[Tests] pin full texture staging extents beside scattered upload regions

MobileGL/MG_Pipe/MGPipeTypes.h

@@ -1266,7 +1266,7 @@ namespace MobileGL::MG_Pipe {
         // bytes an untransformed level shadow?
         Uint8 SourceIsVerbatimLevelShadow;
         // P5 (b1): DOES THIS RESOURCE HAVE A LIVE HOST WRITER RIGHT NOW? One byte out of the
-        // pad, so MGP_ASSERT_POD(MGPSubData, 72) below does not move.
+        // original pad; the complete mip extent below is a separate payload extension.
         //
         // It is here rather than on MGPResourceDesc, and that is a ruling with a reason. The
         // fact is CONTENT-shaped - "someone may be writing these bytes without telling you" -

MobileGL/MG_Remote/Client/SlotCaps.h

@@ -54,8 +54,8 @@
 // Converted, because the fallback is right:
 //   FenceSync used this fallback through P5. P5b §9 moved it to class B: the frontend
 //   now calls the emitter and the server preserves the optional/native-null fallback.
-//   GL_Texture.cpp:6537 GetTextureImage      -> the frontend's own CPU readback, which is exact
-//   GL_Texture.cpp:6799 GetTexImage          -> the same
+//   GetTexImage/GetTextureImage now emit owned texture readback replies. Their
+//   split path must never use the frontend shadow after GPU writes.
 //   GL_Getter.cpp x2 GetGpuTimestampNs and GL_Query.cpp's query probes now use their
 //   timer/occlusion/primitive capability bits. An advertised path emits real query
 //   records; only an unavailable native capability reports COUNTER_BITS 0.

MobileGL/MG_Test/Pipe/TextureEmitTest.cpp

@@ -515,6 +515,10 @@ TEST(TextureEmit, AScatteredUploadCarriesTheLevelShadowsStridesAndNotZero) {
                                     IntVec3{2, 2, 1});
     Textures().DrainTextureSubData(Ctx());
     const Vector<MGPSubRegion> regions = Textures().LastRegions();
+    const auto& record = Textures().LastSubData();
+    EXPECT_EQ(record.LevelWidth, 256u);
+    EXPECT_EQ(record.LevelHeight, 256u);
+    EXPECT_EQ(record.LevelDepth, 1u);
     ASSERT_GE(regions.size(), 2u);
     // A SUB-RECT'S ROWS ARE NOT CONTIGUOUS IN THE SHADOW, so it must carry the LEVEL's pitches -
     // not its own width - or the staging planner on the far side repacks the wrong bytes.