diff --git a/apps/web/vite.config.ts b/apps/web/vite.config.ts
index c0f372ec..e47f76b0 100644
--- a/apps/web/vite.config.ts
+++ b/apps/web/vite.config.ts
@@ -284,7 +284,7 @@ export default defineConfig({
       ? false
       : {
           resolveDependencies: (_filename, dependencies) => dependencies.filter((dependency) =>
-            !/(?:vendor-code-highlight|vendor-(?:mermaid|D3|tiptap|prosemirror|floating|codemirror|x6|infographic|zod)|vendor~(?:wasm|emacs-lisp)-|vendor-radix(?!-slot)|ui-primitives|ui-button-tooltip|i18n-ja-)/.test(dependency),
+            !/(?:vendor-code-highlight|vendor-(?:mermaid|D3|tiptap|prosemirror|floating|codemirror|x6|infographic|zod|streamdown)|vendor~(?:wasm|emacs-lisp)-|vendor-radix(?!-slot)|ui-primitives|ui-button-tooltip|i18n-ja-)/.test(dependency),
           ),
         },
     rolldownOptions: {
diff --git a/scripts/verify-web-performance.mjs b/scripts/verify-web-performance.mjs
index 6fef67a2..a570544e 100644
--- a/scripts/verify-web-performance.mjs
+++ b/scripts/verify-web-performance.mjs
@@ -27,7 +27,7 @@ assert.deepEqual(
 );
 assert.doesNotMatch(serviceWorker, /edgeever-offline-shell/, "PWA must not retain a versioned offline HTML shell");
 const modulePreloads = indexHtml.match(/<link rel="modulepreload"[^>]+>/g)?.join("\n") ?? "";
-const initialOptionalPattern = /vendor-code-highlight|vendor-D3|beautiful-mermaid|vendor-(?:mermaid|tiptap|prosemirror|floating|codemirror|x6|infographic)|vendor~(?:wasm|emacs-lisp)-|ui-primitives|mermaid\.core|[^"']*Diagram(?:EditorPane)?-/;
+const initialOptionalPattern = /vendor-code-highlight|vendor-D3|beautiful-mermaid|vendor-(?:mermaid|tiptap|prosemirror|floating|codemirror|x6|infographic|streamdown)|vendor~(?:wasm|emacs-lisp)-|ui-primitives|mermaid\.core|[^"']*Diagram(?:EditorPane)?-/;
 assert.doesNotMatch(modulePreloads, initialOptionalPattern, "Optional editor and diagram chunks must remain out of the initial HTML modulepreload list");
 assert.doesNotMatch(modulePreloads, /ui-button-tooltip/, "Button tooltips must load only when a titled button is rendered");
 assert.doesNotMatch(modulePreloads, /vendor-radix(?!-slot)/, "Radix overlays must remain out of the initial HTML modulepreload list");
@@ -40,9 +40,10 @@ assert.ok(initialModulePreloadBytes <= INITIAL_MODULE_PRELOAD_BUDGET, `Initial m
 const DEFAULT_CHUNK_WARNING_BYTES = 500 * 1024;
 // Shiki, loaded with the infographic conversation, keeps the Oniguruma wasm
 // engine and the Emacs Lisp grammar above 500 KiB. AntV Infographic stays one
-// atomic deferred chunk so its registries initialize in order. All of these
-// stay off the initial modulepreload list.
-const allowedLargeChunkPattern = /^(?:vendor-(?:code-highlight|beautiful-mermaid|mermaid-(?:layout|render)|codemirror|x6|infographic)|vendor~(?:wasm|emacs-lisp)-|.*Diagram-).*\.js$/;
+// atomic deferred chunk so its registries initialize in order. Streamdown
+// keeps the unified/micromark parser graph atomic for the same reason; it
+// loads with the note editor. All of these stay off the initial modulepreload list.
+const allowedLargeChunkPattern = /^(?:vendor-(?:code-highlight|beautiful-mermaid|mermaid-(?:layout|render)|codemirror|x6|infographic|streamdown)|vendor~(?:wasm|emacs-lisp)-|.*Diagram-).*\.js$/;
 const largeChunks = readdirSync(join(distDirectory, "assets"))
   .filter((name) => name.endsWith(".js"))
   .map((name) => ({ name, size: statSync(join(distDirectory, "assets", name)).size }))