diff --git a/.github/workflows/scripts-ios.yml b/.github/workflows/scripts-ios.yml
index 3c8b0b6315..37d21d3026 100644
--- a/.github/workflows/scripts-ios.yml
+++ b/.github/workflows/scripts-ios.yml
@@ -420,6 +420,16 @@ jobs:
           CN1SS_REPORT_TITLE: 'iOS Metal screenshot updates'
           CN1SS_SUCCESS_MESSAGE: '✅ Native iOS Metal screenshot tests passed.'
           CN1SS_COMMENT_LOG_PREFIX: '[run-ios-device-tests-metal]'
+          # Enable Apple's Metal API Validation in the simulator. Catches
+          # render-pass / pipeline-state mismatches at the moment they
+          # happen (issue #5103: stencil pixel-format mismatch shipped in
+          # four consecutive 7.0.x releases because no test exercised the
+          # validation layer). assert mode crashes the app on the first
+          # validation error -- the missed CN1SS:SUITE:FINISHED marker
+          # then fails this step. run-ios-ui-tests.sh forwards both vars
+          # to the launched app via simctl --setenv.
+          MTL_DEBUG_LAYER: '1'
+          MTL_DEBUG_LAYER_ERROR_MODE: 'assert'
         run: |
           set -euo pipefail
           mkdir -p "${ARTIFACTS_DIR}"
diff --git a/scripts/run-ios-ui-tests.sh b/scripts/run-ios-ui-tests.sh
index 6d1400154b..2f0a8f180a 100755
--- a/scripts/run-ios-ui-tests.sh
+++ b/scripts/run-ios-ui-tests.sh
@@ -625,6 +625,24 @@ APP_PROCESS_NAME="${WRAPPER_NAME%.app}"
 
   LAUNCH_LOG="$ARTIFACTS_DIR/simctl-launch.log"
 
+  # Thread Metal validation env vars (if set in the caller's environment)
+  # through to the launched app. simctl on Xcode 26 does NOT take a
+  # --setenv flag (`xcrun simctl help launch` confirms); the documented
+  # mechanism is exporting SIMCTL_CHILD_<NAME>=<value> in the shell that
+  # invokes simctl, which the launch helper unwraps into <NAME>=<value>
+  # for the child. CI's Metal job sets MTL_DEBUG_LAYER /
+  # MTL_DEBUG_LAYER_ERROR_MODE at the step level so iOS render-pass /
+  # pipeline-state mismatches (issue #5103) abort the app immediately
+  # instead of producing undefined behaviour off-CI.
+  if [ -n "${MTL_DEBUG_LAYER:-}" ]; then
+    export SIMCTL_CHILD_MTL_DEBUG_LAYER="${MTL_DEBUG_LAYER}"
+    ri_log "Forwarding MTL_DEBUG_LAYER=${MTL_DEBUG_LAYER} to simulator app (via SIMCTL_CHILD_)"
+  fi
+  if [ -n "${MTL_DEBUG_LAYER_ERROR_MODE:-}" ]; then
+    export SIMCTL_CHILD_MTL_DEBUG_LAYER_ERROR_MODE="${MTL_DEBUG_LAYER_ERROR_MODE}"
+    ri_log "Forwarding MTL_DEBUG_LAYER_ERROR_MODE=${MTL_DEBUG_LAYER_ERROR_MODE} to simulator app (via SIMCTL_CHILD_)"
+  fi
+
   launch_simulator_app() {
     local target="$1"
     local attempt=1