diff --git a/src/gpu/ganesh/ops/OpsTask.cpp b/src/gpu/ganesh/ops/OpsTask.cpp
index d7e49fe50b6..ca522761d32 100644
--- a/src/gpu/ganesh/ops/OpsTask.cpp
+++ b/src/gpu/ganesh/ops/OpsTask.cpp
@@ -38,9 +38,24 @@
 #include <cstddef>
 #include <cstdint>
 #include <functional>
+#include <map>
 #include <memory>
 #include <utility>
 
+// === [STENCIL-POC] Instrumentation =========================================
+// Tracks, per stencil GrAttachment*, the union of regions that have actually
+// been cleared via VK_ATTACHMENT_LOAD_OP_CLEAR (which is renderArea-scoped).
+// Detects when a kLoad is issued over a region that was never cleared, which
+// on a non-zeroing Vulkan driver loads uninitialised VRAM into the stencil
+// buffer that the Redbook cover pass then exposes to getImageData().
+namespace {
+struct StencilPocTracker {
+    std::map<const void*, SkIRect> cleared;  // attachment* -> union of cleared
+};
+StencilPocTracker& StencilPoc() { static StencilPocTracker t; return t; }
+}  // namespace
+// ===========================================================================
+
 class GrDrawingManager;
 enum GrSurfaceOrigin : int;
 
@@ -617,6 +632,71 @@ bool OpsTask::onExecute(GrOpFlushState* flushState) {
             break;
     }
 
+    // === [STENCIL-POC] =====================================================
+    if (stencil) {
+        const SkISize dims = stencil->dimensions();
+        const SkIRect full = SkIRect::MakeSize(dims);
+        const GrBackendApi api = renderTarget->backendFormat().backend();
+        const char* be = (api == GrBackendApi::kVulkan)   ? "Vulkan"
+                       : (api == GrBackendApi::kOpenGL)   ? "OpenGL"
+                       : (api == GrBackendApi::kMetal)    ? "Metal"
+                       : (api == GrBackendApi::kDirect3D) ? "D3D"
+                                                          : "?";
+        const char* opName = (stencilLoadOp == GrLoadOp::kClear)   ? "kClear"
+                           : (stencilLoadOp == GrLoadOp::kLoad)    ? "kLoad"
+                           : (stencilLoadOp == GrLoadOp::kDiscard) ? "kDiscard"
+                                                                   : "?";
+        fprintf(stderr,
+                "[STENCIL-POC] backend=%s stencil=%p rt=%p dims=%dx%d loadOp=%s "
+                "renderArea=[%d,%d,%d,%d] initialContent=%d hasInitClear=%d\n",
+                be,
+                (void*)stencil, (void*)renderTarget, dims.width(), dims.height(),
+                opName, fClippedContentBounds.fLeft, fClippedContentBounds.fTop,
+                fClippedContentBounds.fRight, fClippedContentBounds.fBottom,
+                (int)fInitialStencilContent,
+                stencil->hasPerformedInitialClear() ? 1 : 0);
+        auto& cleared = StencilPoc().cleared;
+        if (stencilLoadOp == GrLoadOp::kClear) {
+            SkIRect& region = cleared[stencil];
+            if (region.isEmpty()) region = fClippedContentBounds;
+            else region.join(fClippedContentBounds);
+            if (!fClippedContentBounds.contains(full)) {
+                fprintf(stderr,
+                        "[STENCIL-POC]   ** PARTIAL initial clear: only "
+                        "[%d,%d,%d,%d] of %dx%d cleared, but "
+                        "fHasPerformedInitialClear will latch TRUE for the "
+                        "WHOLE attachment **\n",
+                        fClippedContentBounds.fLeft, fClippedContentBounds.fTop,
+                        fClippedContentBounds.fRight,
+                        fClippedContentBounds.fBottom, dims.width(),
+                        dims.height());
+            }
+        } else if (stencilLoadOp == GrLoadOp::kLoad &&
+                   fInitialStencilContent == StencilContent::kUserBitsCleared) {
+            auto it = cleared.find(stencil);
+            SkIRect prev = (it != cleared.end()) ? it->second : SkIRect::MakeEmpty();
+            if (!prev.contains(fClippedContentBounds)) {
+                fprintf(stderr,
+                        "[STENCIL-POC]   ******** BUG TRIGGERED ********\n"
+                        "[STENCIL-POC]   stencilLoadOp=kLoad (fallthrough from "
+                        "kUserBitsCleared because hasPerformedInitialClear()=="
+                        "true) over renderArea=[%d,%d,%d,%d], but this stencil "
+                        "attachment was only ever LOAD_OP_CLEAR'd over "
+                        "[%d,%d,%d,%d]. The remainder is uninitialised VkImage "
+                        "memory (vkCreateImage initialLayout=UNDEFINED, never "
+                        "written). VK_ATTACHMENT_LOAD_OP_LOAD will read it; the "
+                        "Redbook cover pass (kNotEqual 0) exposes it to "
+                        "getImageData(). CWE-908.\n"
+                        "[STENCIL-POC]   ********************************\n",
+                        fClippedContentBounds.fLeft, fClippedContentBounds.fTop,
+                        fClippedContentBounds.fRight,
+                        fClippedContentBounds.fBottom, prev.fLeft, prev.fTop,
+                        prev.fRight, prev.fBottom);
+            }
+        }
+    }
+    // =======================================================================
+
     // NOTE: If fMustPreserveStencil is set, then we are executing a surfaceDrawContext that split
     // its opsTask.
     //