diff --git a/packages/runtime-playground/src/editor-command-runners.ts b/packages/runtime-playground/src/editor-command-runners.ts
index abe80bbb..438d529c 100644
--- a/packages/runtime-playground/src/editor-command-runners.ts
+++ b/packages/runtime-playground/src/editor-command-runners.ts
@@ -30,6 +30,7 @@ const EDITOR_PRESENTATION_MIN_OBSERVATION_MS = 4_000
 const EDITOR_PRESENTATION_POLL_MS = 50
 const EDITOR_PRESENTATION_IFRAME_DISCOVERY_MS = 1_000
 const EDITOR_PRESENTATION_MAX_CAPTURE_MS = 10_000
+const EDITOR_PRESENTATION_VERSION_PARAM = "ver"
 const EDITOR_PRESENTATION_CONTRACT_MARKER = "WP_CODEBOX_EDITOR_PRESENTATION_CONTRACT:"
 const EDITOR_VALIDITY_WARNING_SELECTORS = [
   ".block-editor-warning",
@@ -846,11 +847,32 @@ interface EditorPresentationCapture {
   inlineStyleContents: string[]
 }
 
-export function summarizeEditorPresentation(capture: EditorPresentationCapture): BrowserEditorPresentationSummary {
+// A generated stylesheet delivered as an external asset carries its content
+// hash in the canonical cache-busting version parameter rather than in inline
+// marker text. Read that version so bounded external delivery stays observable.
+function externalStylesheetPresentationIdentity(url: string): string | undefined {
+  let version: string | null = null
+  try {
+    version = new URL(url, "https://wp-codebox.invalid").searchParams.get(EDITOR_PRESENTATION_VERSION_PARAM)
+  } catch {
+    return undefined
+  }
+  const identity = version?.trim().toLowerCase()
+  return identity && /^[a-f0-9]{64}$/.test(identity) ? identity : undefined
+}
+
+export function summarizeEditorPresentation(capture: EditorPresentationCapture, expectedIdentities: readonly string[] = []): BrowserEditorPresentationSummary {
   const iframeStylesheetUrls = [...new Set(capture.stylesheetUrls.map((url) => url.trim()).filter(Boolean))].sort()
-  const generatedPresentationIdentities = [...new Set(
-    capture.inlineStyleContents.flatMap((content) => [...content.matchAll(/blocks-engine-presentation:([a-f0-9]{64})/gi)].map((match) => match[1]!.toLowerCase())),
-  )].sort()
+  const inlineIdentities = capture.inlineStyleContents.flatMap((content) => [...content.matchAll(/blocks-engine-presentation:([a-f0-9]{64})/gi)].map((match) => match[1]!.toLowerCase()))
+  // Only an expected identity can be certified from a URL version. An
+  // unrequested or arbitrary version stays out of the observed set so the
+  // expected-set comparison remains fail-closed.
+  const expected = new Set(expectedIdentities.map((identity) => identity.trim().toLowerCase()).filter(Boolean))
+  const externalIdentities = iframeStylesheetUrls.flatMap((url) => {
+    const identity = externalStylesheetPresentationIdentity(url)
+    return identity && expected.has(identity) ? [identity] : []
+  })
+  const generatedPresentationIdentities = [...new Set([...inlineIdentities, ...externalIdentities])].sort()
   return {
     schema: "wp-codebox/editor-presentation/v1",
     canvasDocumentType: capture.canvasDocumentType,
@@ -901,7 +923,7 @@ export async function captureEditorPresentation(page: import("playwright").Page,
       }
     }, { canvasDocumentType, iframeCount: canvasDocumentType === "iframe" ? 1 : 0 }).catch(() => null) as (EditorPresentationCapture & { documentIdentity: string; documentAgeMs: number }) | null
     if (capture) {
-      const summary = summarizeEditorPresentation(capture)
+      const summary = summarizeEditorPresentation(capture, expectedIdentities)
       const fingerprint = `${capture.documentIdentity}\n${JSON.stringify(summary)}`
       const observedAtMs = Date.now()
       const expectedIdentitiesObserved = expectedIdentities.length > 0
diff --git a/tests/editor-actions.test.ts b/tests/editor-actions.test.ts
index 98054d79..19295c55 100644
--- a/tests/editor-actions.test.ts
+++ b/tests/editor-actions.test.ts
@@ -96,6 +96,58 @@ assert.deepEqual(summarizeEditorPresentation({ canvasDocumentType: "parent", ifr
   generatedPresentationIdentities: [],
 })
 
+// Bounded external delivery: a generated stylesheet enqueued as a real asset
+// carries its content hash in the version parameter instead of inline marker
+// text. Automattic/blocks-engine#1478 delivers presentation styles this way.
+const externalIdentityA = "1".repeat(64)
+const externalIdentityB = "2".repeat(64)
+const unrequestedIdentity = "3".repeat(64)
+const externalOnlyPresentation = summarizeEditorPresentation({
+  canvasDocumentType: "iframe",
+  iframeCount: 1,
+  stylesheetUrls: [`https://example.test/wp-content/themes/fixture/assets/a.css?ver=${externalIdentityA.toUpperCase()}`],
+  inlineStyleContents: [],
+}, [externalIdentityA])
+assert.deepEqual(externalOnlyPresentation.generatedPresentationIdentities, [externalIdentityA], "expected external stylesheet version certifies its identity")
+assert.equal(externalOnlyPresentation.generatedPresentationIdentityCount, 1)
+
+// Mixed inline and external delivery contributes both identities exactly once.
+const inlineIdentity = "4".repeat(64)
+assert.deepEqual(summarizeEditorPresentation({
+  canvasDocumentType: "iframe",
+  iframeCount: 1,
+  stylesheetUrls: [`https://example.test/a.css?ver=${externalIdentityA}`, `https://example.test/b.css?ver=${externalIdentityB}`],
+  inlineStyleContents: [`:root{--blocks-engine-presentation:${inlineIdentity};}`],
+}, [externalIdentityA, externalIdentityB]).generatedPresentationIdentities, [externalIdentityA, externalIdentityB, inlineIdentity].sort(), "inline and external identities combine")
+
+// Fail closed: an unrequested hash, a non-hash version, and a missing expected
+// set never manufacture an observed identity from a URL alone.
+assert.deepEqual(summarizeEditorPresentation({
+  canvasDocumentType: "iframe",
+  iframeCount: 1,
+  stylesheetUrls: [
+    `https://example.test/a.css?ver=${unrequestedIdentity}`,
+    "https://example.test/b.css?ver=6.7.1",
+    "https://example.test/c.css",
+  ],
+  inlineStyleContents: [],
+}, [externalIdentityA]).generatedPresentationIdentities, [], "unrequested and non-hash versions are not identities")
+assert.deepEqual(summarizeEditorPresentation({
+  canvasDocumentType: "iframe",
+  iframeCount: 1,
+  stylesheetUrls: [`https://example.test/a.css?ver=${externalIdentityA}`],
+  inlineStyleContents: [],
+}).generatedPresentationIdentities, [], "no expected set certifies no external identity")
+
+// A delayed stylesheet that has not yet appeared leaves the expected identity
+// unobserved rather than reporting it as satisfied.
+assert.deepEqual(summarizeEditorPresentation({
+  canvasDocumentType: "iframe",
+  iframeCount: 1,
+  stylesheetUrls: [`https://example.test/a.css?ver=${externalIdentityA}`],
+  inlineStyleContents: [],
+}, [externalIdentityA, externalIdentityB]).generatedPresentationIdentities, [externalIdentityA], "a not-yet-loaded stylesheet stays unobserved")
+
 const idleCanvas = await captureEditorIdleCanvas({
   evaluate: async (callback: () => unknown) => {
     const globals = globalThis as typeof globalThis & { document?: unknown; getComputedStyle?: unknown }