diff --git a/.changeset/inline-portable-text-hydration.md b/.changeset/inline-portable-text-hydration.md
new file mode 100644
index 0000000000..59d78a9382
--- /dev/null
+++ b/.changeset/inline-portable-text-hydration.md
@@ -0,0 +1,5 @@
+---
+"emdash": patch
+---
+
+Fixes the inline Portable Text editor failing to hydrate in development when visual editing is enabled. The editor's code-block extension loads lowlight, which default-imports a CommonJS highlight.js module. The Vite client optimizer now pre-bundles `lowlight`, `highlight.js`, and `highlight.js/lib/core` so the deep CJS import is wrapped with ESM interop before it reaches the browser.
diff --git a/e2e/tests/visual-editing.spec.ts b/e2e/tests/visual-editing.spec.ts
index ad4cfa142c..2d6ab42da1 100644
--- a/e2e/tests/visual-editing.spec.ts
+++ b/e2e/tests/visual-editing.spec.ts
@@ -99,6 +99,22 @@ test.describe("Inline Editor", () => {
 		await enableEditMode(page);
 	});
 
+	test("PT editor shows up in visual editing mode", async ({ page }) => {
+		await gotoWithRetry(page, POST_WITH_IMAGE_PATH);
+
+		const editor = page.locator(".emdash-inline-editor");
+		await expect(editor).toBeVisible({ timeout: 15000 });
+
+		// The island failed to hydrate with zero height when highlight.js/lib/core
+		// was served raw as CommonJS, so also assert some static content rendered
+		// inside the editor rather than disappearing.
+		const box = await editor.boundingBox();
+		expect(box).not.toBeNull();
+		expect(box!.height).toBeGreaterThan(0);
+		await expect(editor.locator("text=Text before image.")).toBeVisible();
+		await expect(editor.locator("text=Text after image.")).toBeVisible();
+	});
+
 	test("loads without crashing on posts with image blocks", async ({ page }) => {
 		await gotoWithRetry(page, POST_WITH_IMAGE_PATH);
 
diff --git a/packages/core/src/astro/integration/vite-config.ts b/packages/core/src/astro/integration/vite-config.ts
index 8a8cbe987c..98a0b7d90f 100644
--- a/packages/core/src/astro/integration/vite-config.ts
+++ b/packages/core/src/astro/integration/vite-config.ts
@@ -572,9 +572,17 @@ export function createViteConfig(
 		optimizeDeps: {
 			// When using source, don't pre-bundle JS — let Vite transform on the fly for HMR.
 			// When using dist, pre-bundle to avoid re-optimization on first hydration.
+			// lowlight pulls in a CommonJS highlight.js entry, so the inline Portable
+			// Text editor requires these to be pre-bundled with ESM interop in dev.
 			include: useSource
-				? ["@astrojs/react/client.js"]
-				: ["@emdash-cms/admin", "@astrojs/react/client.js"],
+				? ["@astrojs/react/client.js", "lowlight", "highlight.js", "highlight.js/lib/core"]
+				: [
+						"@emdash-cms/admin",
+						"@astrojs/react/client.js",
+						"lowlight",
+						"highlight.js",
+						"highlight.js/lib/core",
+					],
 			exclude: cloudflare ? ["virtual:emdash"] : [...NODE_NATIVE_EXTERNALS, "virtual:emdash"],
 		},
 	};
diff --git a/packages/core/tests/unit/astro/vite-config.test.ts b/packages/core/tests/unit/astro/vite-config.test.ts
index 0b547587b6..79fde2ce15 100644
--- a/packages/core/tests/unit/astro/vite-config.test.ts
+++ b/packages/core/tests/unit/astro/vite-config.test.ts
@@ -171,6 +171,44 @@ describe("createViteConfig use-sync-external-store shim aliasing", () => {
 	}
 });
 
+describe("createViteConfig inline Portable Text hydration deps", () => {
+	const monorepoDemoRoot = new URL("../../../../../demos/simple/", import.meta.url);
+	const externalProjectRoot = new URL("file:///workspace/emdash-site/");
+
+	function buildConfig(root: URL) {
+		return createViteConfig(
+			{
+				serializableConfig: {},
+				resolvedConfig: {} as never,
+				pluginDescriptors: [],
+				astroConfig: {
+					root,
+					adapter: { name: "@astrojs/node" },
+				} as AstroConfig,
+			},
+			"dev",
+		);
+	}
+
+	it("pre-bundles lowlight and highlight.js in source-mode dev", () => {
+		const config = buildConfig(monorepoDemoRoot);
+		const include = config.optimizeDeps?.include ?? [];
+
+		expect(include).toContain("lowlight");
+		expect(include).toContain("highlight.js");
+		expect(include).toContain("highlight.js/lib/core");
+	});
+
+	it("pre-bundles lowlight and highlight.js in external dist-mode dev", () => {
+		const config = buildConfig(externalProjectRoot);
+		const include = config.optimizeDeps?.include ?? [];
+
+		expect(include).toContain("lowlight");
+		expect(include).toContain("highlight.js");
+		expect(include).toContain("highlight.js/lib/core");
+	});
+});
+
 describe("createViteConfig Astro logger optimization", () => {
 	const astroSevenRoot = new URL("../../../../../demos/cloudflare/", import.meta.url);
 	const astroSixRoot = new URL("../../../../../docs/", import.meta.url);