diff --git a/codex-cli/src/utils/agent/exec.ts b/codex-cli/src/utils/agent/exec.ts
index f0177979..9c763ef5 100644
--- a/codex-cli/src/utils/agent/exec.ts
+++ b/codex-cli/src/utils/agent/exec.ts
@@ -9,6 +9,7 @@ import { exec as rawExec } from "./sandbox/raw-exec.js";
 import { formatCommandForDisplay } from "../../format-command.js";
 import fs from "fs";
 import os from "os";
+import path from "path";
 import { parse } from "shell-quote";
 import { resolvePathAgainstWorkdir } from "src/approvals.js";
 
@@ -63,7 +64,7 @@ export function exec(
 
 export function execApplyPatch(
   patchText: string,
-  workdir: string | undefined,
+  workdir: string | undefined = undefined,
 ): ExecResult {
   // This is a temporary measure to understand what are the common base commands
   // until we start persisting and uploading rollouts
@@ -72,8 +73,20 @@ export function execApplyPatch(
     const result = process_patch(
       patchText,
       (p) => fs.readFileSync(resolvePathAgainstWorkdir(p, workdir), "utf8"),
-      (p, c) =>
-        fs.writeFileSync(resolvePathAgainstWorkdir(p, workdir), c, "utf8"),
+      (p, c) => {
+        const resolvedPath = resolvePathAgainstWorkdir(p, workdir);
+
+        // Ensure the parent directory exists before writing the file. This
+        // mirrors the behaviour of the standalone apply_patch CLI (see
+        // write_file() in apply-patch.ts) and prevents errors when adding a
+        // new file in a not‑yet‑created sub‑directory.
+        const dir = path.dirname(resolvedPath);
+        if (dir !== ".") {
+          fs.mkdirSync(dir, { recursive: true });
+        }
+
+        fs.writeFileSync(resolvedPath, c, "utf8");
+      },
       (p) => fs.unlinkSync(resolvePathAgainstWorkdir(p, workdir)),
     );
     return {
diff --git a/codex-cli/tests/exec-apply-patch.test.ts b/codex-cli/tests/exec-apply-patch.test.ts
new file mode 100644
index 00000000..d28411fa
--- /dev/null
+++ b/codex-cli/tests/exec-apply-patch.test.ts
@@ -0,0 +1,44 @@
+import { execApplyPatch } from "../src/utils/agent/exec.js";
+import fs from "fs";
+import os from "os";
+import path from "path";
+import { test, expect } from "vitest";
+
+/**
+ * This test verifies that `execApplyPatch()` is able to add a new file whose
+ * parent directory does not yet exist. Prior to the fix, the call would throw
+ * because `fs.writeFileSync()` could not create intermediate directories. The
+ * test creates an isolated temporary directory to avoid polluting the project
+ * workspace.
+ */
+test("execApplyPatch creates missing directories when adding a file", () => {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "apply-patch-test-"));
+
+  // Ensure we start from a clean slate.
+  const nestedFileRel = path.join("foo", "bar", "baz.txt");
+  const nestedFileAbs = path.join(tmpDir, nestedFileRel);
+  expect(fs.existsSync(nestedFileAbs)).toBe(false);
+
+  const patch = `*** Begin Patch\n*** Add File: ${nestedFileRel}\n+hello new world\n*** End Patch`;
+
+  // Run execApplyPatch() with cwd switched to tmpDir so that the relative
+  // path in the patch is resolved inside the temporary location.
+  const prevCwd = process.cwd();
+  try {
+    process.chdir(tmpDir);
+
+    const result = execApplyPatch(patch);
+    expect(result.exitCode).toBe(0);
+    expect(result.stderr).toBe("");
+  } finally {
+    process.chdir(prevCwd);
+  }
+
+  // The file (and its parent directories) should have been created with the
+  // expected contents.
+  const fileContents = fs.readFileSync(nestedFileAbs, "utf8");
+  expect(fileContents).toBe("hello new world");
+
+  // Cleanup to keep tmpdir tidy.
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+});