diff --git a/docs/eve-migration-roadmap.md b/docs/eve-migration-roadmap.md
index f9d48a6..d4d20fe 100644
--- a/docs/eve-migration-roadmap.md
+++ b/docs/eve-migration-roadmap.md
@@ -286,6 +286,14 @@ Exit criteria:
 
 Recently cut:
 
+- The web reference now has a schema-backed layout probe for the
+  `embedded-surface` fixture. `scripts/run-web-reference-layout-probe-smoke.ps1`
+  builds the browser lowerer, runs Chrome headless through
+  `tools/web-reference/run-layout-probe.mjs`, writes
+  `gamecult.eve.web_layout_probe.v1` evidence under
+  `artifacts/web-reference-layout-probe/latest/embedded-surface.json`, and
+  parity consumes that artifact so `web:embedded-surface:bounding-boxes` is
+  measured runtime evidence instead of `pending-runtime-probe`.
 - The conformance export now carries `screenshotComparisonMetrics[]` records.
   Runtime owners get structure, color-token, bounding-box, and text-presence
   metrics per runtime/fixture pair without relying on byte-identical screenshots
diff --git a/docs/parity-testing-harness.md b/docs/parity-testing-harness.md
index 41fc2d4..2b27e91 100644
--- a/docs/parity-testing-harness.md
+++ b/docs/parity-testing-harness.md
@@ -434,6 +434,14 @@ box records name whether authored layout boxes exist or whether a runtime still
 owes a capture/layout probe. A missing Unity, Electron, TUI, or Direct2D capture
 body therefore appears as `pending-capture`, not as fake visual parity.
 
+The web reference has the first measured bounding-box probe. The harness runs
+`scripts/run-web-reference-layout-probe-smoke.ps1`, which builds the browser
+lowerer and uses Chrome headless to write
+`artifacts/web-reference-layout-probe/latest/embedded-surface.json` as
+`gamecult.eve.web_layout_probe.v1`. Parity consumes that artifact and marks
+`web:embedded-surface:bounding-boxes` as `pass` with
+`evidenceLayer: runtime-layout-probe`.
+
 The fixture matrix also includes `embedded-surface`, which proves that nested
 CultMesh document slots survive the shared surface contract. The web reference,
 Flutter parity body, Unity UI Toolkit lowerer, iOS UIKit renderer, and native
@@ -501,9 +509,8 @@ Pending runtimes are allowed. Silent fake parity is not.
 
 ## Next Cuts
 
-1. Attach runtime-owned image/layout probes to the screenshot comparison metric
-   lane so bounding-box records can move from `pending-runtime-probe` or
-   `pending-capture` to measured runtime evidence.
+1. Extend runtime-owned image/layout probes beyond web `embedded-surface`,
+   starting with Sai VN in web and the Unity/Electron/TUI capture blockers.
 2. Normalize text scale and font loading across web, Flutter Android, Flutter
    desktop, and iOS.
 3. Give iOS a real `vn.stage` scene compositor instead of compact stacked
diff --git a/packages/eve-browser-lowering/dist/index.js b/packages/eve-browser-lowering/dist/index.js
index c1a9573..32b9bce 100644
--- a/packages/eve-browser-lowering/dist/index.js
+++ b/packages/eve-browser-lowering/dist/index.js
@@ -2109,6 +2109,10 @@ function withJapaneseGuiFallback(stack) {
 function assignId(element, node) {
     if (node.id)
         element.id = node.id;
+    if (node.id)
+        element.dataset.eveNodeId = node.id;
+    if (node.kind)
+        element.dataset.eveKind = node.kind;
 }
 function objectProps(value) {
     return value && typeof value === "object" && !Array.isArray(value) ? value : {};
diff --git a/packages/eve-browser-lowering/src/index.ts b/packages/eve-browser-lowering/src/index.ts
index 25c1aa2..b94a177 100644
--- a/packages/eve-browser-lowering/src/index.ts
+++ b/packages/eve-browser-lowering/src/index.ts
@@ -2454,6 +2454,8 @@ function withJapaneseGuiFallback(stack: string): string {
 
 function assignId(element: HTMLElement, node: EveSurfaceComponent): void {
   if (node.id) element.id = node.id;
+  if (node.id) element.dataset.eveNodeId = node.id;
+  if (node.kind) element.dataset.eveKind = node.kind;
 }
 
 function objectProps(value: unknown): Record<string, unknown> {
diff --git a/schemas/gamecult.eve.web_layout_probe.v1.schema.json b/schemas/gamecult.eve.web_layout_probe.v1.schema.json
new file mode 100644
index 0000000..abd26a4
--- /dev/null
+++ b/schemas/gamecult.eve.web_layout_probe.v1.schema.json
@@ -0,0 +1,108 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "gamecult.eve.web_layout_probe.v1",
+  "title": "Eve Web Layout Probe",
+  "type": "object",
+  "required": [
+    "schema",
+    "runtimeId",
+    "providerId",
+    "surfaceId",
+    "fixtureId",
+    "generatedAt",
+    "viewport",
+    "summary",
+    "nodes"
+  ],
+  "properties": {
+    "schema": {
+      "const": "gamecult.eve.web_layout_probe.v1"
+    },
+    "runtimeId": {
+      "const": "web"
+    },
+    "providerId": {
+      "type": "string",
+      "minLength": 1
+    },
+    "surfaceId": {
+      "type": "string",
+      "minLength": 1
+    },
+    "fixtureId": {
+      "type": "string",
+      "minLength": 1
+    },
+    "generatedAt": {
+      "type": "string",
+      "minLength": 1
+    },
+    "viewport": {
+      "type": "object",
+      "required": ["width", "height"],
+      "properties": {
+        "width": {
+          "type": "number"
+        },
+        "height": {
+          "type": "number"
+        }
+      },
+      "additionalProperties": true
+    },
+    "summary": {
+      "type": "object",
+      "required": ["nodeCount", "measuredNodeCount", "zeroAreaCount"],
+      "properties": {
+        "nodeCount": {
+          "type": "number"
+        },
+        "measuredNodeCount": {
+          "type": "number"
+        },
+        "zeroAreaCount": {
+          "type": "number"
+        }
+      },
+      "additionalProperties": true
+    },
+    "nodes": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "required": ["nodeId", "kind", "rect"],
+        "properties": {
+          "nodeId": {
+            "type": "string",
+            "minLength": 1
+          },
+          "kind": {
+            "type": "string",
+            "minLength": 1
+          },
+          "rect": {
+            "type": "object",
+            "required": ["x", "y", "width", "height"],
+            "properties": {
+              "x": {
+                "type": "number"
+              },
+              "y": {
+                "type": "number"
+              },
+              "width": {
+                "type": "number"
+              },
+              "height": {
+                "type": "number"
+              }
+            },
+            "additionalProperties": true
+          }
+        },
+        "additionalProperties": true
+      }
+    }
+  },
+  "additionalProperties": true
+}
diff --git a/scripts/run-conformance-consumer-smoke.ps1 b/scripts/run-conformance-consumer-smoke.ps1
index 9f89975..2b2b7e2 100644
--- a/scripts/run-conformance-consumer-smoke.ps1
+++ b/scripts/run-conformance-consumer-smoke.ps1
@@ -47,6 +47,7 @@ try {
     --expect-schema gamecult.eve.provider_handoff.v1 `
     --expect-schema gamecult.eve.electron_shell_projection.v1 `
     --expect-schema gamecult.eve.tui_grid.v1 `
+    --expect-schema gamecult.eve.web_layout_probe.v1 `
     --expect-capability-gap runtime:Fensalir:direct2d:capture:missing `
     --expect-world-lowering-coverage aetheria:aetheria.daemon.game:web-reference:claimed:Eve:web `
     --expect-world-lowering-coverage aetheria:aetheria.daemon.game:unity-uitoolkit:claimed:EveUnity:unity-uitoolkit `
@@ -65,7 +66,7 @@ try {
     --expect-screenshot-metric web:embedded-surface:structure:pass `
     --expect-screenshot-metric web:embedded-surface:color-tokens:pass `
     --expect-screenshot-metric web:embedded-surface:text-presence:pass `
-    --expect-screenshot-metric web:embedded-surface:bounding-boxes:pending-runtime-probe `
+    --expect-screenshot-metric web:embedded-surface:bounding-boxes:pass `
     --expect-screenshot-metric electron-shell:aetheria-world:bounding-boxes:pending-capture `
     --expect-capability-gap "split-target:EveUnity:EveUnity:proof:Tagged UPM release" `
     --expect-conformance-handoff
diff --git a/scripts/run-eveconformance-handoff-smoke.ps1 b/scripts/run-eveconformance-handoff-smoke.ps1
index 49835c6..e85377d 100644
--- a/scripts/run-eveconformance-handoff-smoke.ps1
+++ b/scripts/run-eveconformance-handoff-smoke.ps1
@@ -92,6 +92,7 @@ foreach ($contract in @(
   "gamecult.eve.provider_handoff.v1",
   "gamecult.eve.electron_shell_projection.v1",
   "gamecult.eve.tui_grid.v1",
+  "gamecult.eve.web_layout_probe.v1",
   "gamecult.eve.runtime_capability.v1",
   "gamecult.eve.runtime_lifecycle.v1",
   "gamecult.eve.runtime_split_handoff.v1"
@@ -128,6 +129,7 @@ if (Test-Path -LiteralPath (Join-Path $absoluteExportDirectory "index.json")) {
     "gamecult.eve.provider_handoff.v1",
     "gamecult.eve.electron_shell_projection.v1",
     "gamecult.eve.tui_grid.v1",
+    "gamecult.eve.web_layout_probe.v1",
     "gamecult.eve.runtime_capability.v1",
     "gamecult.eve.runtime_lifecycle.v1",
     "gamecult.eve.runtime_split_handoff.v1",
diff --git a/scripts/run-parity-harness.ps1 b/scripts/run-parity-harness.ps1
index c4c6230..6cda988 100644
--- a/scripts/run-parity-harness.ps1
+++ b/scripts/run-parity-harness.ps1
@@ -13,6 +13,7 @@ $env:EVE_PARITY_OUTPUT = if ([System.IO.Path]::IsPathRooted($OutputDirectory)) {
 
 Push-Location $projectRoot
 try {
+  & (Join-Path $PSScriptRoot "run-web-reference-layout-probe-smoke.ps1")
   node .\tools\parity\run-parity.mjs
   & (Join-Path $PSScriptRoot "run-eveconformance-handoff-smoke.ps1")
   & (Join-Path $PSScriptRoot "run-plugin-handoff-smoke.ps1")
diff --git a/scripts/run-runtime-owner-conformance-consumer-smoke.ps1 b/scripts/run-runtime-owner-conformance-consumer-smoke.ps1
index caa374b..9ff8da3 100644
--- a/scripts/run-runtime-owner-conformance-consumer-smoke.ps1
+++ b/scripts/run-runtime-owner-conformance-consumer-smoke.ps1
@@ -47,6 +47,7 @@ node $consumerScript $consumerExport `
   --expect-schema gamecult.eve.runtime_split_handoff.v1 `
   --expect-schema gamecult.eve.electron_shell_projection.v1 `
   --expect-schema gamecult.eve.tui_grid.v1 `
+  --expect-schema gamecult.eve.web_layout_probe.v1 `
   --expect-runtime-status web:active `
   --expect-runtime-status windows-flutter:active `
   --expect-runtime-status linux-flutter:active `
@@ -126,7 +127,7 @@ node $consumerScript $consumerExport `
   --expect-screenshot-metric web:embedded-surface:structure:pass `
   --expect-screenshot-metric web:embedded-surface:color-tokens:pass `
   --expect-screenshot-metric web:embedded-surface:text-presence:pass `
-  --expect-screenshot-metric web:embedded-surface:bounding-boxes:pending-runtime-probe `
+  --expect-screenshot-metric web:embedded-surface:bounding-boxes:pass `
   --expect-screenshot-metric unity-scene:aetheria-world:bounding-boxes:pending-capture `
   --expect-screenshot-metric electron-shell:aetheria-world:bounding-boxes:pending-capture `
   --expect-screenshot-metric tui:aetheria-world:bounding-boxes:pending-capture `
diff --git a/scripts/run-web-reference-layout-probe-smoke.ps1 b/scripts/run-web-reference-layout-probe-smoke.ps1
new file mode 100644
index 0000000..f6a4dd7
--- /dev/null
+++ b/scripts/run-web-reference-layout-probe-smoke.ps1
@@ -0,0 +1,59 @@
+param(
+  [string] $ProviderId = "gamecult.eve.embedded-demo",
+  [string] $FixtureId = "embedded-surface",
+  [string] $OutputPath = "artifacts\web-reference-layout-probe\latest\embedded-surface.json",
+  [int] $Port = 8892,
+  [int] $Width = 1280,
+  [int] $Height = 720
+)
+
+$ErrorActionPreference = "Stop"
+
+$projectRoot = Split-Path -Parent $PSScriptRoot
+$absoluteOutputPath = if ([System.IO.Path]::IsPathRooted($OutputPath)) {
+  $OutputPath
+} else {
+  Join-Path $projectRoot $OutputPath
+}
+
+Push-Location $projectRoot
+try {
+  npm --prefix packages/eve-browser-lowering run build | Out-Host
+  if ($LASTEXITCODE -ne 0) {
+    throw "Eve browser lowering build failed with exit code $LASTEXITCODE"
+  }
+
+  node .\tools\web-reference\run-layout-probe.mjs `
+    --provider $ProviderId `
+    --fixture $FixtureId `
+    --output $OutputPath `
+    --port $Port `
+    --width $Width `
+    --height $Height | Out-Host
+  if ($LASTEXITCODE -ne 0) {
+    throw "Web reference layout probe failed with exit code $LASTEXITCODE"
+  }
+
+  if (-not (Test-Path $absoluteOutputPath)) {
+    throw "Web reference layout probe did not write output: $absoluteOutputPath"
+  }
+  $probe = Get-Content $absoluteOutputPath -Raw | ConvertFrom-Json
+  if ($probe.schema -ne "gamecult.eve.web_layout_probe.v1") {
+    throw "Unexpected web layout probe schema: $($probe.schema)"
+  }
+  if ($probe.runtimeId -ne "web") {
+    throw "Unexpected web layout probe runtime: $($probe.runtimeId)"
+  }
+  if ($probe.providerId -ne $ProviderId) {
+    throw "Unexpected web layout probe provider: $($probe.providerId)"
+  }
+  if ($probe.fixtureId -ne $FixtureId) {
+    throw "Unexpected web layout probe fixture: $($probe.fixtureId)"
+  }
+  if ($probe.summary.measuredNodeCount -le 0) {
+    throw "Web layout probe measured no node boxes."
+  }
+  Write-Host "Web reference layout probe smoke passed: $absoluteOutputPath"
+} finally {
+  Pop-Location
+}
diff --git a/tools/conformance/eveconformance-handoff.json b/tools/conformance/eveconformance-handoff.json
index 280bd52..05b94ee 100644
--- a/tools/conformance/eveconformance-handoff.json
+++ b/tools/conformance/eveconformance-handoff.json
@@ -28,6 +28,7 @@
         "schemas/gamecult.eve.provider_handoff.v1.schema.json",
         "schemas/gamecult.eve.electron_shell_projection.v1.schema.json",
         "schemas/gamecult.eve.tui_grid.v1.schema.json",
+        "schemas/gamecult.eve.web_layout_probe.v1.schema.json",
         "schemas/gamecult.eve.runtime_capability.v1.schema.json",
         "schemas/gamecult.eve.runtime_lifecycle.v1.schema.json",
         "schemas/gamecult.eve.runtime_split_handoff.v1.schema.json",
@@ -92,6 +93,7 @@
     "gamecult.eve.provider_handoff.v1",
     "gamecult.eve.electron_shell_projection.v1",
     "gamecult.eve.tui_grid.v1",
+    "gamecult.eve.web_layout_probe.v1",
     "gamecult.eve.runtime_capability.v1",
     "gamecult.eve.runtime_lifecycle.v1",
     "gamecult.eve.runtime_split_handoff.v1"
diff --git a/tools/parity/parity-manifest.json b/tools/parity/parity-manifest.json
index 712eb83..68e1234 100644
--- a/tools/parity/parity-manifest.json
+++ b/tools/parity/parity-manifest.json
@@ -24,6 +24,7 @@
     "gamecult.eve.runtime_split_handoff.v1": "schemas/gamecult.eve.runtime_split_handoff.v1.schema.json",
     "gamecult.eve.runtime_release_request.v1": "schemas/gamecult.eve.runtime_release_request.v1.schema.json",
     "gamecult.eve.runtime_capture_request.v1": "schemas/gamecult.eve.runtime_capture_request.v1.schema.json",
+    "gamecult.eve.web_layout_probe.v1": "schemas/gamecult.eve.web_layout_probe.v1.schema.json",
     "gamecult.eve.provider_scenario.v1": "schemas/gamecult.eve.provider_scenario.v1.schema.json",
     "gamecult.eve.provider_advertisement.v1": "schemas/gamecult.eve.provider_advertisement.v1.schema.json",
     "gamecult.eve.provider_handoff.v1": "schemas/gamecult.eve.provider_handoff.v1.schema.json",
@@ -1112,7 +1113,17 @@
       },
       "capture": {
         "status": "chrome-headless",
-        "note": "Chrome headless captures phone, tablet, and desktop PNGs through the provider query parameter."
+        "note": "Chrome headless captures phone, tablet, and desktop PNGs through the provider query parameter.",
+        "layoutProbes": [
+          {
+            "fixtureId": "embedded-surface",
+            "providerId": "gamecult.eve.embedded-demo",
+            "surfaceId": "gamecult.eve.embedded-demo",
+            "schema": "gamecult.eve.web_layout_probe.v1",
+            "path": "artifacts/web-reference-layout-probe/latest/embedded-surface.json",
+            "runner": "scripts/run-web-reference-layout-probe-smoke.ps1"
+          }
+        ]
       }
     },
     {
diff --git a/tools/parity/run-parity.mjs b/tools/parity/run-parity.mjs
index 9e8e995..ea034f9 100644
--- a/tools/parity/run-parity.mjs
+++ b/tools/parity/run-parity.mjs
@@ -2503,6 +2503,47 @@ function buildColorTokenMetric(runtime, fixture) {
 }
 
 function buildBoundingBoxMetric(runtime, fixture) {
+  const layoutProbe = readRuntimeLayoutProbe(runtime, fixture.id);
+  if (layoutProbe.config) {
+    if (layoutProbe.document && !layoutProbe.errors.length) {
+      const measured = Number(layoutProbe.document.summary?.measuredNodeCount || 0);
+      const total = Number(layoutProbe.document.summary?.nodeCount || 0);
+      return buildScreenshotMetric(runtime, fixture, {
+        metricKind: "bounding-boxes",
+        status: measured > 0 ? "pass" : "fail",
+        score: ratio(measured, total),
+        expected: {
+          schema: layoutProbe.config.schema || "",
+          path: layoutProbe.config.path || "",
+          providerId: layoutProbe.config.providerId || "",
+          surfaceId: layoutProbe.config.surfaceId || "",
+        },
+        actual: {
+          nodeCount: total,
+          measuredNodeCount: measured,
+          zeroAreaCount: Number(layoutProbe.document.summary?.zeroAreaCount || 0),
+          path: layoutProbe.config.path || "",
+        },
+        evidenceLayer: "runtime-layout-probe",
+        detail: "Compares runtime-owned DOM bounding boxes from the web reference layout probe.",
+      });
+    }
+    return buildScreenshotMetric(runtime, fixture, {
+      metricKind: "bounding-boxes",
+      status: "fail",
+      score: 0,
+      expected: {
+        schema: layoutProbe.config.schema || "",
+        path: layoutProbe.config.path || "",
+      },
+      actual: {
+        errors: layoutProbe.errors,
+      },
+      evidenceLayer: "runtime-layout-probe",
+      detail: "Declared runtime layout probe exists, but the artifact is missing or invalid.",
+    });
+  }
+
   const captureStatus = runtime.capture?.status || "";
   const runtimeHasCaptureBody = ["chrome-headless", "ssh-png", "adb-png", "golden", "ssh-golden"].includes(captureStatus);
   let status = "pass";
@@ -2564,7 +2605,7 @@ function buildScreenshotMetric(runtime, fixture, metric) {
     score: Number(metric.score.toFixed(3)),
     expected: metric.expected,
     actual: metric.actual,
-    evidenceLayer: "surface-structure",
+    evidenceLayer: metric.evidenceLayer || "surface-structure",
     detail: metric.detail,
   };
 }
@@ -2573,6 +2614,37 @@ function ratio(numerator, denominator) {
   return denominator ? Math.max(0, Math.min(1, numerator / denominator)) : 1;
 }
 
+function readRuntimeLayoutProbe(runtime, fixtureId) {
+  const config = (runtime.capture?.layoutProbes || []).find(candidate => candidate.fixtureId === fixtureId);
+  if (!config) return { config: null, document: null, errors: [] };
+  const errors = [];
+  const probePath = config.path || "";
+  const absoluteProbePath = path.join(repoRoot, probePath);
+  if (!probePath || !existsSync(absoluteProbePath)) {
+    return { config, document: null, errors: [`${probePath || "layoutProbe.path"}:missing`] };
+  }
+  let document;
+  try {
+    document = JSON.parse(readFileSync(absoluteProbePath, "utf8"));
+  } catch (error) {
+    return { config, document: null, errors: [`${probePath}:invalid-json:${error instanceof Error ? error.message : String(error)}`] };
+  }
+  if (config.schema && document.schema !== config.schema) errors.push(`${probePath}:schema:expected ${config.schema} got ${document.schema || ""}`);
+  if (config.providerId && document.providerId !== config.providerId) errors.push(`${probePath}:providerId:expected ${config.providerId} got ${document.providerId || ""}`);
+  if (config.surfaceId && document.surfaceId !== config.surfaceId) errors.push(`${probePath}:surfaceId:expected ${config.surfaceId} got ${document.surfaceId || ""}`);
+  if (document.fixtureId !== fixtureId) errors.push(`${probePath}:fixtureId:expected ${fixtureId} got ${document.fixtureId || ""}`);
+  const schemaPath = config.schema ? manifest.schemas?.[config.schema] : "";
+  if (schemaPath) {
+    try {
+      const schema = JSON.parse(readFileSync(path.join(repoRoot, schemaPath), "utf8"));
+      errors.push(...validateSchemaSubset(schema, document, `layoutProbe:${fixtureId}`));
+    } catch (error) {
+      errors.push(`${schemaPath}:unreadable:${error instanceof Error ? error.message : String(error)}`);
+    }
+  }
+  return { config, document, errors };
+}
+
 function collectSplitTargetBlockers(report) {
   return (report.splitTargets || []).flatMap(target => target.blockerRecords || []);
 }
diff --git a/tools/web-reference/run-layout-probe.mjs b/tools/web-reference/run-layout-probe.mjs
new file mode 100644
index 0000000..b7a56ef
--- /dev/null
+++ b/tools/web-reference/run-layout-probe.mjs
@@ -0,0 +1,191 @@
+import { createServer } from "node:http";
+import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { existsSync, readFile as readFileCallback } from "node:fs";
+import { spawn } from "node:child_process";
+import os from "node:os";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const repoRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "../..");
+const args = parseArgs(process.argv.slice(2));
+const port = Number(args.port || 8892);
+const debugPort = Number(args.debugPort || 18892);
+const providerId = args.provider || "gamecult.eve.embedded-demo";
+const fixtureId = args.fixture || "embedded-surface";
+const width = Number(args.width || 1280);
+const height = Number(args.height || 720);
+const outputPath = path.resolve(repoRoot, args.output || `artifacts/web-reference-layout-probe/latest/${fixtureId}.json`);
+
+const server = createStaticServer(repoRoot);
+await new Promise(resolve => server.listen(port, "127.0.0.1", resolve));
+const profile = await mkdtemp(path.join(os.tmpdir(), "eve-web-layout-probe-"));
+
+try {
+  const url = `http://127.0.0.1:${port}/web/layout-probe.html?provider=${encodeURIComponent(providerId)}&fixture=${encodeURIComponent(fixtureId)}`;
+  const probe = await runChromeProbe(url, profile);
+  if (probe.error) throw new Error(probe.error);
+  if (probe.schema !== "gamecult.eve.web_layout_probe.v1") throw new Error(`Unexpected probe schema: ${probe.schema || ""}`);
+  if (probe.runtimeId !== "web") throw new Error(`Unexpected probe runtime: ${probe.runtimeId || ""}`);
+  if (probe.providerId !== providerId) throw new Error(`Unexpected probe provider: ${probe.providerId || ""}`);
+  if (probe.fixtureId !== fixtureId) throw new Error(`Unexpected probe fixture: ${probe.fixtureId || ""}`);
+  if (!probe.summary?.measuredNodeCount) throw new Error("Web layout probe measured no node boxes.");
+  await mkdir(path.dirname(outputPath), { recursive: true });
+  await writeFile(outputPath, `${JSON.stringify(probe, null, 2)}\n`);
+  console.log(outputPath);
+} finally {
+  server.close();
+  await rm(profile, { recursive: true, force: true });
+}
+
+function createStaticServer(root) {
+  const types = {
+    ".html": "text/html; charset=utf-8",
+    ".js": "text/javascript; charset=utf-8",
+    ".css": "text/css; charset=utf-8",
+    ".json": "application/json; charset=utf-8",
+    ".eve": "text/plain; charset=utf-8",
+  };
+  return createServer((request, response) => {
+    const urlPath = decodeURIComponent(new URL(request.url || "/", "http://localhost").pathname);
+    const clean = urlPath === "/" ? "/web/index.html" : urlPath;
+    const file = path.normalize(path.join(root, clean));
+    if (!file.startsWith(root)) {
+      response.writeHead(403);
+      response.end("forbidden");
+      return;
+    }
+    readFileCallback(file, (error, data) => {
+      if (error) {
+        response.writeHead(404);
+        response.end("not found");
+        return;
+      }
+      response.writeHead(200, { "content-type": types[path.extname(file)] || "application/octet-stream" });
+      response.end(data);
+    });
+  });
+}
+
+async function runChromeProbe(url, profile) {
+  const chrome = findChrome();
+  const child = spawn(chrome, [
+    "--headless=new",
+    "--disable-gpu",
+    "--hide-scrollbars",
+    `--remote-debugging-port=${debugPort}`,
+    `--user-data-dir=${profile}`,
+    `--window-size=${width},${height}`,
+    url,
+  ], { stdio: ["ignore", "pipe", "pipe"] });
+  let stderr = "";
+  let closed = false;
+  child.stderr.on("data", chunk => { stderr += chunk; });
+  child.once("close", () => { closed = true; });
+  try {
+    const target = await waitForPageTarget(url);
+    const client = await connectCdp(target.webSocketDebuggerUrl);
+    try {
+      await client.send("Runtime.enable");
+      for (let attempt = 0; attempt < 100; attempt += 1) {
+        const ready = await client.send("Runtime.evaluate", {
+          expression: "document.body?.dataset.probeReady === 'true'",
+          returnByValue: true,
+        });
+        if (ready.result?.value === true) break;
+        await delay(100);
+      }
+      const result = await client.send("Runtime.evaluate", {
+        expression: "document.querySelector('#eve-layout-probe-output')?.textContent || ''",
+        returnByValue: true,
+      });
+      const text = result.result?.value || "";
+      if (!text.trim()) throw new Error("Chrome layout probe produced an empty output document.");
+      return JSON.parse(text);
+    } finally {
+      client.close();
+    }
+  } finally {
+    if (!closed) {
+      child.kill();
+      await new Promise(resolve => child.once("close", resolve));
+    }
+    if (stderr && process.env.EVE_DEBUG_WEB_LAYOUT_PROBE) process.stderr.write(stderr);
+  }
+}
+
+async function waitForPageTarget(url) {
+  for (let attempt = 0; attempt < 100; attempt += 1) {
+    try {
+      const response = await fetch(`http://127.0.0.1:${debugPort}/json`);
+      const targets = await response.json();
+      const target = targets.find(candidate => candidate.type === "page" && candidate.url === url)
+        || targets.find(candidate => candidate.type === "page" && candidate.url?.includes("/web/layout-probe.html"));
+      if (target?.webSocketDebuggerUrl) return target;
+    } catch {
+      // Chrome is still booting.
+    }
+    await delay(100);
+  }
+  throw new Error(`Timed out waiting for Chrome DevTools target on port ${debugPort}.`);
+}
+
+function connectCdp(webSocketUrl) {
+  return new Promise((resolve, reject) => {
+    const socket = new WebSocket(webSocketUrl);
+    let nextId = 1;
+    const pending = new Map();
+    socket.addEventListener("open", () => {
+      resolve({
+        send(method, params = {}) {
+          const id = nextId++;
+          socket.send(JSON.stringify({ id, method, params }));
+          return new Promise((messageResolve, messageReject) => {
+            pending.set(id, { resolve: messageResolve, reject: messageReject });
+          });
+        },
+        close() {
+          socket.close();
+        },
+      });
+    });
+    socket.addEventListener("message", event => {
+      const message = JSON.parse(event.data);
+      if (!message.id || !pending.has(message.id)) return;
+      const callbacks = pending.get(message.id);
+      pending.delete(message.id);
+      if (message.error) callbacks.reject(new Error(message.error.message || JSON.stringify(message.error)));
+      else callbacks.resolve(message.result || {});
+    });
+    socket.addEventListener("error", reject);
+  });
+}
+
+function delay(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+function findChrome() {
+  const candidates = [
+    process.env.CHROME_PATH,
+    path.join(process.env.ProgramFiles || "", "Google/Chrome/Application/chrome.exe"),
+    path.join(process.env["ProgramFiles(x86)"] || "", "Google/Chrome/Application/chrome.exe"),
+    "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+    "/usr/bin/google-chrome",
+    "/usr/bin/chromium",
+    "/usr/bin/chromium-browser",
+  ].filter(Boolean);
+  const chrome = candidates.find(candidate => existsSync(candidate));
+  if (!chrome) throw new Error("Chrome is required for the web layout probe and was not found.");
+  return chrome;
+}
+
+function parseArgs(values) {
+  const parsed = {};
+  for (let index = 0; index < values.length; index += 1) {
+    const key = values[index];
+    if (!key.startsWith("--")) continue;
+    parsed[key.slice(2)] = values[index + 1];
+    index += 1;
+  }
+  return parsed;
+}
diff --git a/web/eve-runtime-capability.json b/web/eve-runtime-capability.json
index 12fc411..7e2260b 100644
--- a/web/eve-runtime-capability.json
+++ b/web/eve-runtime-capability.json
@@ -92,6 +92,10 @@
       "status": "chrome-headless",
       "evidencePaths": [
         "scripts/capture-web-reference.ps1",
+        "scripts/run-web-reference-layout-probe-smoke.ps1",
+        "tools/web-reference/run-layout-probe.mjs",
+        "web/layout-probe.html",
+        "web/layout-probe.js",
         "scripts/run-parity-smoke.ps1",
         "tools/parity/render-contact-sheet.py"
       ],
diff --git a/web/layout-probe.html b/web/layout-probe.html
new file mode 100644
index 0000000..bbdcad9
--- /dev/null
+++ b/web/layout-probe.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1" />
+  <title>Eve Web Layout Probe</title>
+  <link rel="stylesheet" href="../packages/eve-browser-lowering/styles.css" />
+  <link rel="stylesheet" href="./cultui-reference-overrides.css" />
+</head>
+<body>
+  <main id="app" class="surface"></main>
+  <pre id="eve-layout-probe-output"></pre>
+  <script type="module" src="./layout-probe.js"></script>
+</body>
+</html>
diff --git a/web/layout-probe.js b/web/layout-probe.js
new file mode 100644
index 0000000..4ed49c9
--- /dev/null
+++ b/web/layout-probe.js
@@ -0,0 +1,110 @@
+import { renderEveSurface } from "../packages/eve-browser-lowering/dist/index.js";
+import { compileEveDsl } from "./eve-dsl.js";
+
+const app = document.querySelector("#app");
+const output = document.querySelector("#eve-layout-probe-output");
+const params = new URLSearchParams(location.search);
+const providerId = params.get("provider") || "gamecult.eve.embedded-demo";
+const fixtureId = params.get("fixture") || providerId;
+
+try {
+  const provider = await loadProvider(providerId);
+  const surfaceEntry = provider.surfaces?.[0];
+  if (!surfaceEntry) throw new Error(`${providerId} has no advertised surface`);
+  const state = await loadSurface(surfaceEntry);
+  renderEveSurface(state, app, {
+    activeSurfaceId: state.surface?.id,
+    body: document.body,
+    clientId: "browser.reference.layout-probe",
+    provider,
+    source: "web layout probe",
+  });
+  await animationFrame();
+  await animationFrame();
+  publishProbe(measureLayout(state, provider, fixtureId));
+} catch (error) {
+  publishProbe({
+    schema: "gamecult.eve.web_layout_probe.v1",
+    runtimeId: "web",
+    providerId,
+    surfaceId: "",
+    fixtureId,
+    generatedAt: new Date().toISOString(),
+    viewport: { width: window.innerWidth, height: window.innerHeight },
+    summary: { nodeCount: 0, measuredNodeCount: 0, zeroAreaCount: 0 },
+    nodes: [],
+    error: error instanceof Error ? error.message : String(error),
+  });
+}
+
+async function loadProvider(requestedProviderId) {
+  const response = await fetch("./local-provider-catalog.json", { cache: "no-store" });
+  const catalog = await response.json();
+  const provider = (catalog.providers || []).find(candidate =>
+    candidate.providerId === requestedProviderId || candidate.aliases?.includes(requestedProviderId));
+  if (!provider) throw new Error(`Unknown local provider: ${requestedProviderId}`);
+  if (!provider.advertisement) return provider;
+  const advertisement = await (await fetch(provider.advertisement, { cache: "no-store" })).json();
+  return {
+    ...advertisement,
+    ...provider,
+    surfaces: provider.surfaces || advertisement.surfaces || [],
+    localAdvertisement: advertisement,
+  };
+}
+
+async function loadSurface(surface) {
+  const response = await fetch(surface.url, { cache: "no-store" });
+  const source = await response.text();
+  if (surface.transport === "local-eve-dsl") return compileEveDsl(source);
+  if (surface.transport === "local-json") return JSON.parse(source);
+  throw new Error(`Unsupported probe surface transport: ${surface.transport}`);
+}
+
+function measureLayout(state, provider, fixture) {
+  const nodes = [...document.querySelectorAll("[data-eve-node-id]")].map(element => {
+    const rect = element.getBoundingClientRect();
+    return {
+      nodeId: element.dataset.eveNodeId || "",
+      kind: element.dataset.eveKind || "",
+      rect: {
+        x: round(rect.x),
+        y: round(rect.y),
+        width: round(rect.width),
+        height: round(rect.height),
+      },
+    };
+  }).filter(node => node.nodeId && node.kind);
+  const measuredNodeCount = nodes.filter(node => node.rect.width > 0 && node.rect.height > 0).length;
+  return {
+    schema: "gamecult.eve.web_layout_probe.v1",
+    runtimeId: "web",
+    providerId: state.providerId || provider.providerId || providerId,
+    surfaceId: state.surface?.id || "",
+    fixtureId: fixture,
+    generatedAt: new Date().toISOString(),
+    viewport: {
+      width: window.innerWidth,
+      height: window.innerHeight,
+    },
+    summary: {
+      nodeCount: nodes.length,
+      measuredNodeCount,
+      zeroAreaCount: nodes.length - measuredNodeCount,
+    },
+    nodes,
+  };
+}
+
+function publishProbe(probeDocument) {
+  output.textContent = JSON.stringify(probeDocument, null, 2);
+  document.body?.setAttribute?.("data-probe-ready", "true");
+}
+
+function animationFrame() {
+  return new Promise(resolve => requestAnimationFrame(() => resolve()));
+}
+
+function round(value) {
+  return Math.round(value * 100) / 100;
+}