diff --git a/README.md b/README.md
index 6916e6a..d8ef6e8 100644
--- a/README.md
+++ b/README.md
@@ -193,3 +193,8 @@ This optional test uses `web-ext` and a disposable headless profile, never your
 signed-in profile. It exercises the real compatibility layer against local
 HTTP fixtures and verifies lifecycle delivery and foreground-tab preservation.
 It does not exercise the signed-in Codex native transport.
+
+For an unsigned review build on macOS, Linux, or Windows, commit the working tree
+and run `pnpm package:portable`. It uses Node and Git, writes ZIP/XPI and a review-source
+archive under `dist/`, and preserves the release checksum filenames. The existing
+PowerShell packaging command and release workflow are unchanged.
diff --git a/package.json b/package.json
index 6326b76..c0ba6fe 100644
--- a/package.json
+++ b/package.json
@@ -7,8 +7,10 @@
   "scripts": {
     "check": "node scripts/check-version.mjs && node scripts/verify-extension.mjs",
     "version:set": "node scripts/set-version.mjs",
-    "test": "npm run check && node tests/test-amo-auth.mjs && node tests/test-companion-required.mjs && node tests/test-sidepanel-focus-compat.mjs && node tests/test-sidepanel-host-access.mjs && node tests/test-sidepanel-bootstrap.mjs && node tests/test-sidepanel-companion-setup.mjs && node tests/test-chatgpt-feature-parity.mjs && node tests/test-firefox-compat.mjs && node tests/test-editing-assets.mjs && node tests/test-native-host.mjs",
+    "test": "npm run check && node tests/test-amo-auth.mjs && node tests/test-companion-required.mjs && node tests/test-sidepanel-focus-compat.mjs && node tests/test-sidepanel-host-access.mjs && node tests/test-sidepanel-bootstrap.mjs && node tests/test-sidepanel-companion-setup.mjs && node tests/test-chatgpt-feature-parity.mjs && node tests/test-firefox-compat.mjs && node tests/test-editing-assets.mjs && node tests/test-native-host.mjs && node tests/test-portable-packaging.mjs",
     "package": "powershell -NoProfile -ExecutionPolicy Bypass -File scripts/package-extension.ps1",
-    "test:live": "node tests/test-firefox-lifecycle-live.mjs"
+    "test:package": "node tests/test-portable-packaging.mjs",
+    "test:live": "node tests/test-firefox-lifecycle-live.mjs",
+    "package:portable": "node scripts/package-extension.mjs"
   }
 }
diff --git a/scripts/package-extension.mjs b/scripts/package-extension.mjs
new file mode 100644
index 0000000..7517b81
--- /dev/null
+++ b/scripts/package-extension.mjs
@@ -0,0 +1,131 @@
+#!/usr/bin/env node
+import fs from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { execFileSync } from "node:child_process";
+import { deflateRawSync } from "node:zlib";
+import { createHash } from "node:crypto";
+
+const root = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
+process.chdir(root);
+for (const script of ["check-version.mjs", "verify-extension.mjs"]) {
+  execFileSync(process.execPath, [path.join("scripts", script)], { stdio: "inherit" });
+}
+if (execFileSync("git", ["status", "--porcelain", "--untracked-files=normal"], { encoding: "utf8" }).trim()) {
+  throw new Error("Commit the source before packaging so the source archive matches the extension.");
+}
+// Freeze one tree for both artifacts. Checkout filters (such as autocrlf)
+// and ignored local files must never affect the reviewed package bytes.
+const commit = execFileSync("git", ["rev-parse", "HEAD"], { encoding: "utf8" }).trim();
+const entries = execFileSync("git", ["ls-tree", "-rz", "--full-tree", commit], {
+  encoding: "utf8", maxBuffer: 16 * 1024 * 1024,
+}).split("\0").filter(Boolean).map(entry => {
+  const match = /^(\d+) (\w+) ([a-f\d]+)\t([\s\S]+)$/u.exec(entry);
+  if (!match || match[2] !== "blob" || !["100644", "100755"].includes(match[1])) {
+    throw new Error(`Refusing to package non-regular committed entry ${entry}`);
+  }
+  return { name: match[4], object: match[3], mode: parseInt(match[1], 8) };
+}).sort((a, b) => a.name < b.name ? -1 : a.name > b.name ? 1 : 0);
+const blobs = execFileSync("git", ["cat-file", "--batch"], {
+  input: entries.map(entry => entry.object).join("\n") + "\n",
+  maxBuffer: 256 * 1024 * 1024,
+});
+let cursor = 0;
+const sourceFiles = entries.map(entry => {
+  const end = blobs.indexOf(10, cursor);
+  const header = blobs.subarray(cursor, end).toString("ascii").split(" ");
+  const size = Number(header[2]);
+  if (end < 0 || header[0] !== entry.object || header[1] !== "blob" || !Number.isSafeInteger(size)) {
+    throw new Error(`Invalid committed blob for ${entry.name}`);
+  }
+  cursor = end + 1;
+  const data = blobs.subarray(cursor, cursor + size);
+  cursor += size + 1;
+  return { name: entry.name, data, mode: entry.mode };
+});
+const { version } = JSON.parse(sourceFiles.find(file => file.name === "version.json").data);
+const stem = `codex-computer-use-firefox-zen-${version}`;
+const dist = path.join(root, "dist");
+fs.mkdirSync(dist, { recursive: true });
+
+const crcTable = Array.from({ length: 256 }, (_, value) => {
+  for (let bit = 0; bit < 8; bit++) value = value & 1 ? 0xedb88320 ^ (value >>> 1) : value >>> 1;
+  return value >>> 0;
+});
+function crc32(data) {
+  let crc = 0xffffffff;
+  for (const byte of data) crc = crcTable[(crc ^ byte) & 255] ^ (crc >>> 8);
+  return (crc ^ 0xffffffff) >>> 0;
+}
+
+const files = sourceFiles.filter(file => file.name.startsWith("extension/"))
+  .map(file => ({ name: file.name.slice("extension/".length), data: file.data, mode: file.mode }));
+
+function zip(files) {
+  if (files.length >= 65535) throw new Error("ZIP64 is not supported by this packager.");
+  const parts = [];
+  const central = [];
+  let offset = 0;
+  for (const { name, data, mode } of files) {
+    const filename = Buffer.from(name);
+    const compressed = deflateRawSync(data, { level: 9 });
+    const crc = crc32(data);
+    if (filename.length > 65535 || data.length > 0xffffffff || offset > 0xffffffff) {
+      throw new Error(`ZIP64 is required for ${name}.`);
+    }
+    // ZIP-standard paths, UTF-8 names, and a fixed 1980-01-01 timestamp.
+    const local = Buffer.alloc(30);
+    local.writeUInt32LE(0x04034b50);
+    local.writeUInt16LE(20, 4);
+    local.writeUInt16LE(0x800, 6);
+    local.writeUInt16LE(8, 8);
+    local.writeUInt16LE(0x21, 12);
+    local.writeUInt32LE(crc, 14);
+    local.writeUInt32LE(compressed.length, 18);
+    local.writeUInt32LE(data.length, 22);
+    local.writeUInt16LE(filename.length, 26);
+    const entry = Buffer.alloc(46);
+    entry.writeUInt32LE(0x02014b50);
+    entry.writeUInt16LE((3 << 8) | 20, 4); // Unix creator: preserve committed file modes.
+    entry.writeUInt16LE(20, 6);
+    entry.writeUInt16LE(0x800, 8);
+    entry.writeUInt16LE(8, 10);
+    entry.writeUInt16LE(0x21, 14);
+    entry.writeUInt32LE(crc, 16);
+    entry.writeUInt32LE(compressed.length, 20);
+    entry.writeUInt32LE(data.length, 24);
+    entry.writeUInt16LE(filename.length, 28);
+    entry.writeUInt32LE((mode << 16) >>> 0, 38);
+    entry.writeUInt32LE(offset, 42);
+    parts.push(local, filename, compressed);
+    central.push(entry, filename);
+    offset += local.length + filename.length + compressed.length;
+  }
+  const centralData = Buffer.concat(central);
+  if (offset + centralData.length > 0xffffffff) throw new Error("ZIP64 is required for this archive.");
+  const end = Buffer.alloc(22);
+  end.writeUInt32LE(0x06054b50);
+  end.writeUInt16LE(files.length, 8);
+  end.writeUInt16LE(files.length, 10);
+  end.writeUInt32LE(centralData.length, 12);
+  end.writeUInt32LE(offset, 16);
+  return Buffer.concat([...parts, centralData, end]);
+}
+const archive = zip(files);
+for (const suffix of ["zip", "xpi"]) fs.writeFileSync(path.join(dist, `${stem}.${suffix}`), archive);
+fs.writeFileSync(path.join(dist, `${stem}-source.zip`), zip(sourceFiles));
+
+const artifacts = [`${stem}.zip`, `${stem}.xpi`, `${stem}-source.zip`];
+const checksums = artifacts.map((name) => {
+  const checksum = `${createHash("sha256").update(fs.readFileSync(path.join(dist, name))).digest("hex")}  ${name}\n`;
+  // Preserve the existing release workflow's per-artifact checksum names.
+  fs.writeFileSync(path.join(dist, name.endsWith(".zip") ? name.slice(0, -4) + ".sha256" : name + ".sha256"), checksum);
+  return checksum;
+});
+fs.writeFileSync(path.join(dist, "SHA256SUMS"), checksums.join(""));
+console.log(JSON.stringify({
+  version,
+  commit,
+  files: files.length,
+  artifacts: artifacts.map((name) => ({ path: path.join(dist, name), bytes: fs.statSync(path.join(dist, name)).size })),
+}, null, 2));
diff --git a/tests/test-portable-packaging.mjs b/tests/test-portable-packaging.mjs
new file mode 100644
index 0000000..0e92c75
--- /dev/null
+++ b/tests/test-portable-packaging.mjs
@@ -0,0 +1,65 @@
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { execFileSync } from "node:child_process";
+import { inflateRawSync } from "node:zlib";
+import { fileURLToPath } from "node:url";
+
+const root = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
+const temp = fs.mkdtempSync(path.resolve(os.tmpdir(), "portable-packaging-"));
+let checkout = path.join(temp, "checkout");
+const git = (...args) => execFileSync("git", args, { cwd: checkout, encoding: "utf8" });
+function zipEntries(buffer) {
+  const entries = new Map();
+  let offset = 0;
+  while (buffer.readUInt32LE(offset) === 0x04034b50) {
+    const compressedSize = buffer.readUInt32LE(offset + 18);
+    const nameSize = buffer.readUInt16LE(offset + 26);
+    const extraSize = buffer.readUInt16LE(offset + 28);
+    const name = buffer.subarray(offset + 30, offset + 30 + nameSize).toString();
+    const start = offset + 30 + nameSize + extraSize;
+    entries.set(name, inflateRawSync(buffer.subarray(start, start + compressedSize)));
+    offset = start + compressedSize;
+  }
+  return entries;
+}
+try {
+  execFileSync("git", ["clone", "--quiet", "--no-hardlinks", root, checkout]);
+  // Test the script being edited, even before its parent commit is published.
+  fs.copyFileSync(path.join(root, "scripts/package-extension.mjs"), path.join(checkout, "scripts/package-extension.mjs"));
+  git("add", "scripts/package-extension.mjs");
+  // A disposable fixture must not depend on the contributor's signing key.
+  git("-c", "user.name=Packaging regression", "-c", "user.email=packaging@localhost",
+    "-c", "commit.gpgsign=false", "commit", "--quiet", "--allow-empty", "-m", "Canonical packaging fixture");
+  const { version } = JSON.parse(fs.readFileSync(path.join(checkout, "version.json")));
+  const stem = `codex-computer-use-firefox-zen-${version}`;
+  const build = () => {
+    execFileSync(process.execPath, ["scripts/package-extension.mjs"], { cwd: checkout, stdio: "pipe" });
+    return ["zip", "xpi", "source.zip"].map(suffix => fs.readFileSync(
+      path.join(checkout, "dist", suffix === "source.zip" ? `${stem}-source.zip` : `${stem}.${suffix}`),
+    ));
+  };
+  const baseline = build();
+  assert.deepEqual(baseline[0], baseline[1], "ZIP and XPI must carry identical bytes.");
+  const packaged = zipEntries(baseline[0]);
+  const source = zipEntries(baseline[2]);
+  assert.equal(packaged.size, [...source.keys()].filter(name => name.startsWith("extension/")).length);
+  for (const [name, data] of packaged) {
+    assert.deepEqual(data, source.get(`extension/${name}`), `Review source must contain the exact bytes for ${name}`);
+  }
+  fs.appendFileSync(path.join(checkout, ".git/info/exclude"), "\nextension/debug.log\n");
+  fs.writeFileSync(path.join(checkout, "extension/debug.log"), "ignored local secret\n");
+  assert.equal(git("status", "--porcelain").trim(), "", "The contaminating local file is ignored.");
+  assert.deepEqual(build(), baseline, "Ignored local files must not affect either archive.");
+  const crlfCheckout = path.join(temp, "crlf-checkout");
+  execFileSync("git", ["clone", "--quiet", "--no-hardlinks", "--config", "core.autocrlf=true", checkout, crlfCheckout]);
+  checkout = crlfCheckout;
+  assert.equal(git("status", "--porcelain").trim(), "", "CRLF checkout remains clean.");
+  assert.ok(fs.readFileSync(path.join(checkout, "extension/manifest.json"), "utf8").includes("\r\n"),
+    "The fixture must actually exercise checkout byte conversion.");
+  assert.deepEqual(build(), baseline, "Checkout line-ending filters must not affect committed package bytes.");
+  console.log(JSON.stringify({ ok: true, exactReviewSource: true, ignoredFilesExcluded: true, checkoutFiltersIgnored: true }));
+} finally {
+  fs.rmSync(temp, { recursive: true, force: true });
+}