diff --git a/packages/cli/src/tts/synthesize.cache.test.ts b/packages/cli/src/tts/synthesize.cache.test.ts
new file mode 100644
index 0000000000..f31f4e77d8
--- /dev/null
+++ b/packages/cli/src/tts/synthesize.cache.test.ts
@@ -0,0 +1,106 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import * as fs from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { execFileSync } from "node:child_process";
+
+const paths = vi.hoisted(() => ({ home: "" }));
+vi.mock("node:os", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("node:os")>()),
+  homedir: () => paths.home,
+}));
+vi.mock("node:fs", async (importOriginal) => {
+  const original = await importOriginal<typeof fs>();
+  return { ...original, existsSync: vi.fn(original.existsSync) };
+});
+vi.mock("node:child_process", () => ({ execFileSync: vi.fn() }));
+vi.mock("./python.js", () => ({
+  findPython: () => "test-python",
+  hasPythonPackage: () => true,
+}));
+vi.mock("./manager.js", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("./manager.js")>()),
+  ensureModel: vi.fn().mockResolvedValue("model.onnx"),
+  ensureVoices: vi.fn().mockResolvedValue("voices.bin"),
+}));
+
+describe("synthesis script cache", () => {
+  let cacheDir: string;
+  let scriptPath: string;
+  let outputPath: string;
+
+  beforeEach(() => {
+    vi.resetModules();
+    vi.clearAllMocks();
+    paths.home = fs.mkdtempSync(join(tmpdir(), "hf-tts-cache-"));
+    cacheDir = join(paths.home, ".cache", "hyperframes", "tts");
+    scriptPath = join(cacheDir, "synth-v3.py");
+    outputPath = join(paths.home, "speech.wav");
+    fs.mkdirSync(cacheDir, { recursive: true });
+    vi.mocked(execFileSync).mockImplementation(() => {
+      fs.writeFileSync(outputPath, "stub audio");
+      return JSON.stringify({
+        outputPath,
+        sampleRate: 24000,
+        durationSeconds: 1,
+        langApplied: true,
+      });
+    });
+  });
+
+  afterEach(() => {
+    expect(fs.readdirSync(cacheDir).filter((name) => name.startsWith(".hf-create-"))).toEqual([]);
+    fs.rmSync(paths.home, { recursive: true, force: true });
+  });
+
+  it("creates the script, removes only old script versions, and reuses the current cache", async () => {
+    fs.writeFileSync(join(cacheDir, "synth-v2.py"), "old script");
+    fs.writeFileSync(join(cacheDir, "notes.txt"), "keep");
+    const { synthesize } = await import("./synthesize.js");
+    await synthesize("Hello", outputPath);
+    const script = fs.readFileSync(scriptPath, "utf-8");
+    expect(script).toContain("import kokoro_onnx");
+    expect(script).toContain('"durationSeconds": round(duration, 3)');
+    expect(fs.existsSync(join(cacheDir, "synth-v2.py"))).toBe(false);
+    expect(fs.readFileSync(join(cacheDir, "notes.txt"), "utf-8")).toBe("keep");
+    fs.writeFileSync(scriptPath, "existing current script");
+    await synthesize("Again", outputPath);
+    expect(fs.readFileSync(scriptPath, "utf-8")).toBe("existing current script");
+  });
+
+  it.each(["concurrent file", "dangling symlink"])(
+    "preserves a %s at publication",
+    async (kind) => {
+      const target = join(paths.home, "missing.py");
+      const original = await vi.importActual<typeof fs>("node:fs");
+      let injected = false;
+      vi.mocked(fs.existsSync).mockImplementation((path) => {
+        if (path === scriptPath && !injected) {
+          injected = true;
+          if (kind === "dangling symlink") fs.symlinkSync(target, scriptPath);
+          else fs.writeFileSync(scriptPath, "concurrent script");
+          return false;
+        }
+        return original.existsSync(path);
+      });
+      try {
+        const { synthesize } = await import("./synthesize.js");
+        await synthesize("Hello", outputPath);
+        expect(injected).toBe(true);
+        if (kind === "dangling symlink") {
+          expect(fs.lstatSync(scriptPath).isSymbolicLink()).toBe(true);
+          expect(fs.existsSync(target)).toBe(false);
+        } else {
+          expect(fs.readFileSync(scriptPath, "utf-8")).toBe("concurrent script");
+        }
+        expect(execFileSync).toHaveBeenCalledWith(
+          "test-python",
+          expect.arrayContaining([scriptPath, "model.onnx", "voices.bin", "Hello", outputPath]),
+          expect.objectContaining({ timeout: 300_000 }),
+        );
+      } finally {
+        vi.mocked(fs.existsSync).mockImplementation(original.existsSync);
+      }
+    },
+  );
+});
diff --git a/packages/cli/src/tts/synthesize.ts b/packages/cli/src/tts/synthesize.ts
index 21ee5f52c0..a32f299ebd 100644
--- a/packages/cli/src/tts/synthesize.ts
+++ b/packages/cli/src/tts/synthesize.ts
@@ -1,6 +1,6 @@
 // fallow-ignore-file complexity
 import { execFileSync } from "node:child_process";
-import { existsSync, writeFileSync, mkdirSync, readdirSync, unlinkSync } from "node:fs";
+import { existsSync, mkdirSync, readdirSync, unlinkSync } from "node:fs";
 import { join, dirname, basename } from "node:path";
 import { homedir } from "node:os";
 import {
@@ -11,6 +11,7 @@ import {
   type SupportedLang,
 } from "./manager.js";
 import { findPython, hasPythonPackage } from "./python.js";
+import { writeNewFileSync } from "../utils/writeNewFile.js";
 
 // ---------------------------------------------------------------------------
 // Inline Python script for Kokoro synthesis
@@ -100,7 +101,7 @@ const SCRIPT_PATH = join(SCRIPT_DIR, "synth-v3.py");
 function ensureSynthScript(): string {
   if (!existsSync(SCRIPT_PATH)) {
     mkdirSync(SCRIPT_DIR, { recursive: true });
-    writeFileSync(SCRIPT_PATH, SYNTH_SCRIPT);
+    writeNewFileSync(SCRIPT_PATH, SYNTH_SCRIPT);
     // Best-effort: delete older versioned scripts left behind by previous
     // CLI releases so users don't accumulate stale files in ~/.cache.
     const currentName = basename(SCRIPT_PATH);