diff --git a/packages/web/app/src/components/schema-editor.ts b/packages/web/app/src/components/schema-editor.ts
index 77c489bd2..c6cc0a96a 100644
--- a/packages/web/app/src/components/schema-editor.ts
+++ b/packages/web/app/src/components/schema-editor.ts
@@ -1,6 +1,18 @@
 import { lazy } from 'react';
+// Import from `editor.api` rather than the `monaco-editor` main entry to keep
+// the bundle lean — the main entry auto-registers every basic language, which
+// bloats our client sourcemaps. We opt in to the contributions we actually use
+// via the side-effect imports below.
 import * as monaco from 'monaco-editor/esm/vs/editor/editor.api';
+// Enables the read-only tooltip shown when users type into a read-only model.
 import 'monaco-editor/esm/vs/editor/contrib/readOnlyMessage/browser/contribution.js';
+// Registers the basic GraphQL Monarch tokenizer so `language="graphql"` models
+// get syntax highlighting. Without this, `editor.api` ships no languages.
+import 'monaco-editor/esm/vs/basic-languages/graphql/graphql.contribution.js';
+// Registers the JSON language service (`monaco.languages.json`) — required by
+// the policy naming-convention rule editor, which configures JSON schema
+// diagnostics in `beforeMount`.
+import 'monaco-editor/esm/vs/language/json/monaco.contribution.js';
 import {
   loader,
   DiffEditor as MonacoDiffEditor,
diff --git a/packages/web/app/src/lib/preflight/graphiql-plugin.tsx b/packages/web/app/src/lib/preflight/graphiql-plugin.tsx
index 1776a0aa9..7e48477e2 100644
--- a/packages/web/app/src/lib/preflight/graphiql-plugin.tsx
+++ b/packages/web/app/src/lib/preflight/graphiql-plugin.tsx
@@ -660,7 +660,11 @@ function PreflightModal({
   }, []);
 
   const handleMonacoEditorBeforeMount = useCallback(async (monaco: Monaco) => {
-    if (monaco.languages.typescript) {
+    // Lazy-load the TS language service on first preflight mount if it hasn't
+    // already been registered. `schema-editor.ts` configures Monaco with the
+    // lean `editor.api` entry (no languages bundled), so `monaco.languages
+    // .typescript` is only defined after this side-effect import has run.
+    if (!monaco.languages.typescript) {
       await import('monaco-editor/esm/vs/language/typescript/monaco.contribution');
     }