diff --git a/package.json b/package.json
index 9dfde2719f..b24f168ca6 100644
--- a/package.json
+++ b/package.json
@@ -88,17 +88,7 @@
     "overrides": {
       "rollup": ">=4.59.0",
       "react": "^19.2.8",
-      "react-dom": "^19.2.8",
-      "lexical": "0.49.0",
-      "@lexical/clipboard": "0.49.0",
-      "@lexical/link": "0.49.0",
-      "@lexical/list": "0.49.0",
-      "@lexical/markdown": "0.49.0",
-      "@lexical/plain-text": "0.49.0",
-      "@lexical/react": "0.49.0",
-      "@lexical/rich-text": "0.49.0",
-      "@lexical/selection": "0.49.0",
-      "@lexical/utils": "0.49.0"
+      "react-dom": "^19.2.8"
     }
   }
 }
diff --git a/ui/package.json b/ui/package.json
index 520d91b203..38ccf73e10 100644
--- a/ui/package.json
+++ b/ui/package.json
@@ -33,7 +33,7 @@
     "@dnd-kit/core": "^6.3.1",
     "@dnd-kit/sortable": "^10.0.0",
     "@dnd-kit/utilities": "^3.2.2",
-    "@lexical/link": "0.49.0",
+    "@lexical/link": "0.48.0",
     "@mdxeditor/editor": "^4.2.1",
     "@paperclipai/adapter-claude-local": "workspace:*",
     "@paperclipai/adapter-codex-local": "workspace:*",
@@ -57,7 +57,7 @@
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
     "i18next": "^26.3.6",
-    "lexical": "0.49.0",
+    "lexical": "0.48.0",
     "lucide-react": "^1.32.0",
     "mermaid": "^11.16.1",
     "motion": "^12.42.2",
diff --git a/ui/src/lib/lexical-single-copy.test.ts b/ui/src/lib/lexical-single-copy.test.ts
new file mode 100644
index 0000000000..5ff3eddc4d
--- /dev/null
+++ b/ui/src/lib/lexical-single-copy.test.ts
@@ -0,0 +1,66 @@
+import { readFileSync } from "node:fs";
+import { createRequire } from "node:module";
+import { dirname, join, parse } from "node:path";
+import { describe, expect, it } from "vitest";
+
+/**
+ * Lexical must resolve to exactly one copy across the app and the rich editor.
+ *
+ * The editor registers the app's own nodes (mention-aware links, paste
+ * handling) into MDXEditor's Lexical instance. If the app and MDXEditor load
+ * different copies — or different versions of the same package — Lexical's
+ * `LexicalBuilder` invariant throws during render, the editor falls back to
+ * its raw-source textarea, and every markdown field in the product silently
+ * degrades.
+ *
+ * That is not hypothetical: root `pnpm.overrides` once force-pinned the
+ * Lexical family past the range `@mdxeditor/editor` supports, while leaving
+ * `@lexical/extension` (absent from the override list) on the older line. The
+ * mismatch shipped and broke the editor everywhere. These assertions fail
+ * fast on the resolution graph instead of waiting for a render crash.
+ */
+describe("lexical single copy", () => {
+  const requireFromUi = createRequire(import.meta.url);
+  const mdxEditorEntry = requireFromUi.resolve("@mdxeditor/editor");
+  const requireFromMdxEditor = createRequire(mdxEditorEntry);
+
+  /** These packages block "./package.json" in exports, so read it off disk. */
+  function manifestOf(specifier: string, from: NodeJS.Require): { version: string; dependencies?: Record<string, string> } {
+    let dir = dirname(from.resolve(specifier));
+    const { root } = parse(dir);
+    while (true) {
+      try {
+        return JSON.parse(readFileSync(join(dir, "package.json"), "utf8"));
+      } catch {
+        if (dir === root) throw new Error(`no package.json above ${specifier}`);
+        dir = dirname(dir);
+      }
+    }
+  }
+
+  function versionOf(specifier: string, from: NodeJS.Require): string {
+    return manifestOf(specifier, from).version;
+  }
+
+  it("resolves the same lexical copy for the app and the editor", () => {
+    expect(requireFromMdxEditor.resolve("lexical")).toBe(requireFromUi.resolve("lexical"));
+  });
+
+  it("keeps the app's lexical packages on the editor's version line", () => {
+    const core = versionOf("lexical", requireFromUi);
+    // @lexical/link carries the mention-aware LinkNode the app subclasses, so
+    // a version split here breaks node identity even with one core copy.
+    expect(versionOf("@lexical/link", requireFromUi)).toBe(core);
+    expect(versionOf("lexical", requireFromMdxEditor)).toBe(core);
+    // @lexical/extension owns the LexicalBuilder invariant that throws on a
+    // mixed graph, and it is reached transitively rather than declared.
+    expect(versionOf("@lexical/extension", requireFromMdxEditor)).toBe(core);
+  });
+
+  it("satisfies the editor's declared lexical range", () => {
+    const declared = manifestOf("@mdxeditor/editor", requireFromUi).dependencies?.lexical;
+    const [major, minor] = versionOf("lexical", requireFromUi).split(".");
+    // A caret range on a 0.x version pins the minor: ^0.48.0 means <0.49.0.
+    expect(declared).toBe(`^${major}.${minor}.0`);
+  });
+});