[MG_Impl, MG_IntegrationTest, ci] (P7): the first perturbation block's falsifier is the DirectVulkan entry

- measured with one block removed at a time: without the re-applied block both server halves drop to 1 (DirectGLES 1 / DirectVulkan 1, both entries red); without the first block DirectVulkan drops to 1 (red) while DirectGLES stays at 2 (green), because the GLES backend reads the pack field twice after the neutral pack is installed (3 = the saved-pack read + 2 post-install) and DirectVulkan once (2 = 1 + 1)
- so the >= 2 requirement falsifies the re-applied block on both backends and the first block on DirectVulkan; the CI step runs both backends and needs both, which it already does
- the scenario, hook and CI comments now say exactly that, instead of "removing either block drops it to 1"

.github/workflows/test.yml

@@ -1099,8 +1099,11 @@ jobs:
       # installs the neutral one, the backend's ReadPixels reads it after - and the hook perturbs
       # its oracle once per read, because the ID-49 overwrite inside the window wipes the first
       # perturbation before the second read's compare. A step satisfied by ONE line was satisfied
-      # by either perturbation alone and falsified neither; two is one per read, each falsified on
-      # its own. Measured at landing: 3 (DirectGLES) / 2 (DirectVulkan).
+      # by either perturbation alone and falsified neither. Measured at landing: 3 (DirectGLES,
+      # whose backend reads the field twice after the install) / 2 (DirectVulkan); without the
+      # re-applied perturbation both drop to 1, without the first one DirectVulkan drops to 1
+      # while DirectGLES stays at 2 - so BOTH backends are required, and the first perturbation's
+      # falsifier is the DirectVulkan entry.
       #
       # THE GREEN HALF is the lane run above: the same hook, the same window, with no corruption
       # armed, across 1070 entries at zero divergences.

MobileGL/MG_Impl/Pipe/PipeFill.cpp

@@ -779,8 +779,11 @@ namespace MobileGL::MG_Pipe {
             // GetPixelStoreParameters cannot turn red - and a control that accepted ONE report
             // would never notice, because the saved-pack read still reports through the block
             // above. The VerifySplitReadCorrupted. entries and the CI step therefore require at
-            // least TWO `where=read` reports in the server half: one per block, each falsified
-            // alone (V1 fix round 2).
+            // least TWO `where=read` reports in the server half (V1 fix round 2). Measured: 3 on
+            // DirectGLES (its backend reads the field twice after the install) / 2 on
+            // DirectVulkan; without this block both drop to 1, without the block above
+            // DirectVulkan drops to 1 while DirectGLES's two post-install reports keep it at 2 -
+            // so this block is falsified on both backends and the one above on DirectVulkan.
             if (g_verify.Corrupt && *g_verify.Corrupt == field) {
                 MGPipeApplyVerifyCorruption(g_readScratch, field);
             }

MobileGL/MG_IntegrationTest/Scenarios/PipeVerifyArmingScenario.cpp

@@ -380,7 +380,11 @@ void main() { o_color = vec4(0.25, 0.5, 0.75, 1.0); }
             // after the window's overwrite can turn the post-install read red, because there the
             // stored value IS the neutral pack. A control satisfied by ONE line is satisfied by
             // either block alone and so falsified neither. Measured at landing the server half
-            // carries 3 (DirectGLES) / 2 (DirectVulkan); removing either block drops it to 1.
+            // carries 3 (DirectGLES: the saved-pack read and TWO post-install reads) / 2
+            // (DirectVulkan: one of each). Removing the re-applied block drops both backends to
+            // 1; removing the first block drops DirectVulkan to 1 and leaves DirectGLES at 2, so
+            // the first block's falsifier is the DirectVulkan entry - which is why the CI step
+            // runs both backends and needs both.
             const std::size_t reads = CountReadReports(server, expected);
             EXPECT_GE(reads, std::size_t{2})
                 << "the server half carries " << reads << " `where=read` report(s) for " << expected