diff --git a/skills-manifest.json b/skills-manifest.json
index 11e90f1fa4..ceab4acf60 100644
--- a/skills-manifest.json
+++ b/skills-manifest.json
@@ -50,8 +50,8 @@
       "files": 12
     },
     "media-use": {
-      "hash": "e870f18213f27c8b",
-      "files": 154
+      "hash": "a397849a32047f7e",
+      "files": 156
     },
     "motion-graphics": {
       "hash": "853ac75cbab69036",
diff --git a/skills/media-use/audio/scripts/audio.mjs b/skills/media-use/audio/scripts/audio.mjs
index bc005eeff9..167eb679ca 100644
--- a/skills/media-use/audio/scripts/audio.mjs
+++ b/skills/media-use/audio/scripts/audio.mjs
@@ -39,7 +39,7 @@
 // the generate path it is spawned detached (bgm_pending:true) — run wait-bgm.mjs
 // before assembling.
 
-import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { existsSync, mkdirSync, readFileSync } from "node:fs";
 import { dirname, join, resolve } from "node:path";
 import { fileURLToPath } from "node:url";
 import { heygenAuthHeaders, heygenCredential, loadEnvFromDir } from "./lib/heygen.mjs";
@@ -54,6 +54,7 @@ import {
 import { generateBgmDetached, inferBgmPrompt, retrieveBgm } from "./lib/bgm.mjs";
 import { resolveSfx } from "./lib/sfx.mjs";
 import { mapWithConcurrency } from "./lib/concurrency.mjs";
+import { openAudioMeta } from "./lib/audio-meta.mjs";
 
 const HERE = dirname(fileURLToPath(import.meta.url));
 const argv = process.argv.slice(2);
@@ -115,7 +116,8 @@ const heygenOK = heygenCredential() !== null;
 const headers = heygenOK ? heygenAuthHeaders() : null;
 
 // ── merge base: preserve sections not selected by --only ──────────────────────
-const prev = existsSync(outPath) ? JSON.parse(readFileSync(outPath, "utf8")) : {};
+const audioMeta = openAudioMeta(outPath);
+const prev = audioMeta.value;
 const anomalies = [];
 
 // ── TTS ───────────────────────────────────────────────────────────────────────
@@ -279,7 +281,7 @@ const meta = {
   total_duration_s: totalDuration,
 };
 mkdirSync(dirname(outPath), { recursive: true });
-writeFileSync(outPath, JSON.stringify(meta, null, 2));
+audioMeta.write(meta);
 
 console.log(`✓ audio engine → ${outPath}`);
 console.log(`  heygen: ${heygenOK ? "yes" : "no"}  ·  ran: ${[...only].join(",")}`);
diff --git a/skills/media-use/audio/scripts/lib/audio-meta.mjs b/skills/media-use/audio/scripts/lib/audio-meta.mjs
new file mode 100644
index 0000000000..f3c032a9c4
--- /dev/null
+++ b/skills/media-use/audio/scripts/lib/audio-meta.mjs
@@ -0,0 +1,39 @@
+import { closeSync, ftruncateSync, openSync, readFileSync, writeSync } from "node:fs";
+
+// Keep the merge base and output on the same file even if its pathname changes
+// while audio generation runs. The CLI owns this handle until write or exit.
+export function openAudioMeta(path) {
+  let fd;
+  try {
+    fd = openSync(path, "r+");
+  } catch (error) {
+    if (error.code !== "ENOENT") throw error;
+  }
+  let value = {};
+  if (fd !== undefined) {
+    try {
+      value = JSON.parse(readFileSync(fd, "utf8"));
+    } catch (error) {
+      closeSync(fd);
+      throw error;
+    }
+  }
+  return {
+    value,
+    write(meta) {
+      const bytes = Buffer.from(JSON.stringify(meta, null, 2));
+      // Defer new-file creation until generation succeeds. Never overwrite a
+      // file (or follow a link) that appeared since the missing merge base.
+      if (fd === undefined) fd = openSync(path, "wx");
+      try {
+        let offset = 0;
+        while (offset < bytes.length) {
+          offset += writeSync(fd, bytes, offset, bytes.length - offset, offset);
+        }
+        ftruncateSync(fd, bytes.length);
+      } finally {
+        closeSync(fd);
+      }
+    },
+  };
+}
diff --git a/skills/media-use/audio/scripts/lib/audio-meta.test.mjs b/skills/media-use/audio/scripts/lib/audio-meta.test.mjs
new file mode 100644
index 0000000000..2fa3a68807
--- /dev/null
+++ b/skills/media-use/audio/scripts/lib/audio-meta.test.mjs
@@ -0,0 +1,136 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  mkdtempSync,
+  readFileSync,
+  renameSync,
+  rmSync,
+  statSync,
+  symlinkSync,
+  writeFileSync,
+} from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { spawnSync } from "node:child_process";
+import { fileURLToPath } from "node:url";
+import { openAudioMeta } from "./audio-meta.mjs";
+
+function fixture(t) {
+  const dir = mkdtempSync(join(tmpdir(), "audio-meta-"));
+  t.after(() => rmSync(dir, { recursive: true, force: true }));
+  return dir;
+}
+
+test("updates the read file from byte zero, truncates, and retains its mode", (t) => {
+  const path = join(fixture(t), "meta.json");
+  writeFileSync(path, JSON.stringify({ voices: ["long existing voice metadata"] }), {
+    mode: 0o600,
+  });
+  const originalMode = statSync(path).mode;
+  const handle = openAudioMeta(path);
+  assert.deepEqual(handle.value, { voices: ["long existing voice metadata"] });
+  handle.write({ voices: ["声"] });
+  assert.equal(readFileSync(path, "utf8"), JSON.stringify({ voices: ["声"] }, null, 2));
+  assert.equal(statSync(path).mode, originalMode);
+});
+
+test("pathname replacement cannot redirect the existing-file write", (t) => {
+  const dir = fixture(t);
+  const path = join(dir, "meta.json");
+  const moved = join(dir, "original.json");
+  writeFileSync(path, "{}");
+  const handle = openAudioMeta(path);
+  renameSync(path, moved);
+  writeFileSync(path, "replacement must survive");
+  handle.write({ voices: [] });
+  assert.equal(readFileSync(path, "utf8"), "replacement must survive");
+  assert.deepEqual(JSON.parse(readFileSync(moved, "utf8")), { voices: [] });
+});
+
+test("existing symlink outputs retain their original target even after retargeting", (t) => {
+  const dir = fixture(t);
+  const path = join(dir, "meta.json");
+  const target = join(dir, "target.json");
+  const victim = join(dir, "victim.json");
+  writeFileSync(target, "{}");
+  writeFileSync(victim, "untouched");
+  symlinkSync(target, path);
+  const handle = openAudioMeta(path);
+  rmSync(path);
+  symlinkSync(victim, path);
+  handle.write({ bgm: null });
+  assert.equal(readFileSync(victim, "utf8"), "untouched");
+  assert.deepEqual(JSON.parse(readFileSync(target, "utf8")), { bgm: null });
+});
+
+test("missing output is created only when saved", (t) => {
+  const path = join(fixture(t), "meta.json");
+  const handle = openAudioMeta(path);
+  assert.deepEqual(handle.value, {});
+  assert.throws(() => statSync(path), { code: "ENOENT" });
+  handle.write({ sfx: [] });
+  assert.deepEqual(JSON.parse(readFileSync(path, "utf8")), { sfx: [] });
+});
+
+for (const replacement of ["file", "symlink"]) {
+  test(`new output does not overwrite a racing ${replacement}`, (t) => {
+    const dir = fixture(t);
+    const path = join(dir, "meta.json");
+    const victim = join(dir, "victim.json");
+    const handle = openAudioMeta(path);
+    writeFileSync(victim, "untouched");
+    if (replacement === "symlink") symlinkSync(victim, path);
+    else writeFileSync(path, "untouched");
+    assert.throws(() => handle.write({}), { code: "EEXIST" });
+    assert.equal(readFileSync(path, "utf8"), "untouched");
+    assert.equal(readFileSync(victim, "utf8"), "untouched");
+  });
+}
+
+test("malformed merge base remains an error without changing bytes", (t) => {
+  const path = join(fixture(t), "meta.json");
+  writeFileSync(path, "bad json");
+  assert.throws(() => openAudioMeta(path), SyntaxError);
+  assert.equal(readFileSync(path, "utf8"), "bad json");
+});
+
+test("CLI partial run retains unselected voices, BGM and SFX", (t) => {
+  const dir = fixture(t);
+  const path = join(dir, "meta.json");
+  const request = join(dir, "request.json");
+  const previous = {
+    voices: [{ id: "a", duration_s: 2 }],
+    bgm: { path: "bgm.wav" },
+    sfx: [{ name: "click" }],
+    tts_provider: "kokoro",
+    voice_id: "voice-a",
+  };
+  writeFileSync(path, JSON.stringify(previous));
+  writeFileSync(request, "{}");
+  const result = spawnSync(
+    process.execPath,
+    [
+      fileURLToPath(new URL("../audio.mjs", import.meta.url)),
+      "--request",
+      request,
+      "--hyperframes",
+      dir,
+      "--out",
+      path,
+      "--only",
+      "none",
+    ],
+    {
+      encoding: "utf8",
+      env: {
+        ...process.env,
+        HEYGEN_CONFIG_DIR: dir,
+        HEYGEN_API_KEY: "",
+        HYPERFRAMES_API_KEY: "",
+      },
+    },
+  );
+  assert.equal(result.status, 0, result.stderr);
+  const actual = JSON.parse(readFileSync(path, "utf8"));
+  for (const key of Object.keys(previous)) assert.deepEqual(actual[key], previous[key]);
+});