diff --git a/runner/run.py b/runner/run.py
index b748adf..dd64657 100644
--- a/runner/run.py
+++ b/runner/run.py
@@ -194,6 +194,7 @@
         # Automation cohorts opt into on-demand layout explicitly.
         "launch_profile_args": {
             "all_resources": ("--resource",),
+            "browser_automation": ("--enable-automation",),
         },
     },
     "lightpanda": {
diff --git a/tasks/L1/raw_cdp/v2_diag_layoutmetrics_viewport.json b/tasks/L1/raw_cdp/v2_diag_layoutmetrics_viewport.json
index e916b3a..8be8a3f 100644
--- a/tasks/L1/raw_cdp/v2_diag_layoutmetrics_viewport.json
+++ b/tasks/L1/raw_cdp/v2_diag_layoutmetrics_viewport.json
@@ -1,10 +1,19 @@
 {
   "artifact_profile": "l1_standard",
   "chrome_gate": "off",
-  "description": "[diagnostic lane] This method is on the real framework main path (on_framework_main_path); routed to the diagnostic lane per bench policy. Page.getLayoutMetrics viewport consistency: cssLayoutViewport.clientWidth, cssContentSize.width and the (deprecated) layoutViewport.clientWidth must all agree (780 under the pinned Chrome headless viewport).",
+  "description": "Sets an explicit 780\u00d7600 CSS viewport with DPR 1, then checks layout/content/visual viewport widths. This removes platform-dependent headless window defaults from the contract.",
   "driver": {
     "kind": "raw_cdp",
     "steps": [
+      {
+        "method": "Emulation.setDeviceMetricsOverride",
+        "params": {
+          "width": 780,
+          "height": 600,
+          "deviceScaleFactor": 1,
+          "mobile": false
+        }
+      },
       {
         "method": "Page.getLayoutMetrics",
         "save_result_as": "lm"
@@ -34,6 +43,12 @@
         "kind": "saved_path_equals",
         "name": "lm",
         "path": "layoutViewport.clientWidth"
+      },
+      {
+        "expected": 780,
+        "kind": "saved_path_equals",
+        "name": "lm",
+        "path": "cssVisualViewport.clientWidth"
       }
     ],
     "kind": "inline_assertions"
@@ -50,7 +65,7 @@
     "version.v0_2"
   ],
   "task_id": "v2_diag_layoutmetrics_viewport",
-  "task_version": 1,
+  "task_version": 2,
   "timeouts": {
     "hard_kill_ms": 30000,
     "task_ms": 15000
diff --git a/test/test_unit_checks.py b/test/test_unit_checks.py
index 3e8c03f..ac10288 100644
--- a/test/test_unit_checks.py
+++ b/test/test_unit_checks.py
@@ -446,7 +446,7 @@ def test_moli_all_resources_profile_enables_full_resource_fetch():
     ]
 
 
-def test_browser_automation_profile_is_chrome_only():
+def test_chrome_browser_automation_profile_is_opt_in():
     automation = runner_run.chrome_launch_command(
         pathlib.Path("/tmp/chrome"),
         9336,
@@ -459,7 +459,20 @@ def test_browser_automation_profile_is_chrome_only():
     assert "--enable-automation" in automation
     assert "--enable-automation" not in default
     assert automation[-1] == "about:blank"
-    assert runner_run.engine_serve_args("moli", "browser_automation") == ()
+
+
+@pytest.mark.parametrize("engine", ["moli", "lightpanda", "obscura"])
+def test_browser_automation_profile_only_enables_supported_serve_engines(engine):
+    binary = pathlib.Path("/tmp") / engine
+    default = runner_run.serve_engine_launch_command(engine, binary, 9333)
+    automation = runner_run.serve_engine_launch_command(
+        engine, binary, 9333, "browser_automation"
+    )
+    assert "--enable-automation" not in default
+    if engine == "moli":
+        assert automation == [*default, "--enable-automation"]
+    else:
+        assert automation == default
 
 
 def test_serve_command_keeps_engine_specific_flags_isolated():