diff --git a/npm/code-cli/README.md b/npm/code-cli/README.md
index ed88f94..ad2bd3a 100644
--- a/npm/code-cli/README.md
+++ b/npm/code-cli/README.md
@@ -149,7 +149,9 @@ npm test
 # Dry-run `npm pack` and inspect the published file list
 npm run pack:dry
 
-# Pre-publish guard: version check + tests
+# Pre-publish guard: version check, pin release checksums, tests.
+# Publish only after the GitHub release for v<version> exists: the pin step downloads
+# each release binary and writes checksums.json into the package.
 npm run prepublishOnly
 
 # Full CI/presubmit checks
diff --git a/npm/code-cli/lib/download.mjs b/npm/code-cli/lib/download.mjs
index 1611f58..4e7f7ee 100644
--- a/npm/code-cli/lib/download.mjs
+++ b/npm/code-cli/lib/download.mjs
@@ -10,6 +10,7 @@ import { execFileSync } from "node:child_process";
 import { createHash } from "node:crypto";
 import { existsSync, mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
+import { loadPinnedChecksums, pinnedSha256 } from "./pinned-checksums.mjs";
 import { detectTarget, UnsupportedPlatformError } from "./platform.mjs";
 
 export const RELEASE_BASE = "https://github.com/frontal-labs/code/releases/download";
@@ -51,7 +52,7 @@ export async function fetchSha256(version, assetName) {
   }
 }
 
-async function downloadTo({ version, destDir, log = () => undefined }) {
+async function downloadTo({ version, destDir, log = () => undefined, pinned }) {
   const { target, assetName, binName } = detectTarget();
   const url = releaseAssetUrl(version, assetName);
   log(`Downloading ${assetName} (${target}) from ${url}`);
@@ -72,7 +73,15 @@ async function downloadTo({ version, destDir, log = () => undefined }) {
   if (!verifySha256(buf, expected)) {
     throw new Error(`SHA-256 mismatch for ${assetName}`);
   }
-  log(`Verified SHA-256 for ${assetName}`);
+  // The sidecar comes from the same release as the binary, so it cannot catch a release
+  // that was replaced wholesale. The checksum pinned at publish time can.
+  if (!verifySha256(buf, pinnedSha256(pinned, version, assetName))) {
+    throw new Error(
+      `SHA-256 for ${assetName} does not match the checksum pinned in this npm package. ` +
+        `The release may have been altered after publish; refusing to install it.`,
+    );
+  }
+  log(`Verified SHA-256 for ${assetName} against the pinned checksum`);
 
   const binDir = join(destDir, "vendor", target, "bin");
   mkdirSync(binDir, { recursive: true });
@@ -82,7 +91,12 @@ async function downloadTo({ version, destDir, log = () => undefined }) {
 }
 
 // Public entry point. Returns the resolved binary path under vendor/.
-export async function downloadRelease({ version, destDir, log = () => undefined }) {
+export async function downloadRelease({
+  version,
+  destDir,
+  log = () => undefined,
+  pinned = loadPinnedChecksums(),
+}) {
   if (!version || /dev$/.test(version) || version === "0.0.0") {
     throw new Error(
       `Refusing to download for dev version "${version}". Use a tagged release version.`,
@@ -90,7 +104,7 @@ export async function downloadRelease({ version, destDir, log = () => undefined
   }
   let binPath;
   try {
-    binPath = await downloadTo({ version, destDir, log });
+    binPath = await downloadTo({ version, destDir, log, pinned });
   } catch (e) {
     if (e instanceof UnsupportedPlatformError) throw e;
     throw e;
diff --git a/npm/code-cli/lib/pinned-checksums.mjs b/npm/code-cli/lib/pinned-checksums.mjs
new file mode 100644
index 0000000..649c51e
--- /dev/null
+++ b/npm/code-cli/lib/pinned-checksums.mjs
@@ -0,0 +1,43 @@
+// Checksums pinned into the npm package at publish time.
+//
+// `checksums.json` is written by `scripts/pin-checksums.mjs` from the release binaries
+// during `prepublishOnly`, so it ships inside the npm tarball. The launcher checks a
+// downloaded binary against these hashes as well as the release's `.sha256` sidecar.
+// A tampered GitHub release that replaces a binary and its sidecar still fails here,
+// because the npm package was published from the genuine release.
+
+import { readFileSync } from "node:fs";
+
+export const CHECKSUMS_URL = new URL("../checksums.json", import.meta.url);
+
+// Load the pinned file. Returns null when it is absent (for example, a source checkout
+// that has not been through the publish step).
+export function loadPinnedChecksums(url = CHECKSUMS_URL) {
+  try {
+    return JSON.parse(readFileSync(url, "utf8"));
+  } catch (e) {
+    if (e.code === "ENOENT") return null;
+    throw e;
+  }
+}
+
+// Return the pinned SHA-256 for one asset of one version. Throws when the pinned file is
+// for another version or has no entry for the asset.
+export function pinnedSha256(pinned, version, assetName) {
+  if (!pinned) {
+    throw new Error(
+      `No pinned checksums are bundled with this package, so ${assetName} cannot be verified. ` +
+        `Reinstall a published release, or build from source with \`cargo build --release -p cli\`.`,
+    );
+  }
+  if (pinned.version !== version) {
+    throw new Error(
+      `Bundled checksums are for v${pinned.version}, not v${version}. Reinstall the package for this version.`,
+    );
+  }
+  const hex = pinned.assets?.[assetName];
+  if (!hex) {
+    throw new Error(`No pinned SHA-256 for ${assetName} in v${version}.`);
+  }
+  return hex;
+}
diff --git a/npm/code-cli/lib/platform.mjs b/npm/code-cli/lib/platform.mjs
index 90d50bf..b00bb6f 100644
--- a/npm/code-cli/lib/platform.mjs
+++ b/npm/code-cli/lib/platform.mjs
@@ -28,6 +28,12 @@ const TARGETS = {
   "win32/x64": { target: "x86_64-pc-windows-msvc", ext: ".exe" },
 };
 
+// Every release asset name the launcher can download. The checksum pin script uses this
+// list so the packaged checksums cover every platform, not just the one that publishes.
+export function allAssetNames() {
+  return Object.values(TARGETS).map((entry) => `code-cli-${entry.target}${entry.ext}`);
+}
+
 // Pure helper: resolve a descriptor from explicit platform/arch.
 export function targetFor(platform, arch) {
   const entry = TARGETS[`${platform}/${arch}`];
diff --git a/npm/code-cli/package.json b/npm/code-cli/package.json
index 6733066..ad85267 100644
--- a/npm/code-cli/package.json
+++ b/npm/code-cli/package.json
@@ -26,6 +26,7 @@
   "files": [
     "bin/index.js",
     "lib/**/*.mjs",
+    "checksums.json",
     "scripts/postinstall.sh",
     "README.md"
   ],
diff --git a/npm/code-cli/scripts/pin-checksums.mjs b/npm/code-cli/scripts/pin-checksums.mjs
new file mode 100755
index 0000000..953a4c9
--- /dev/null
+++ b/npm/code-cli/scripts/pin-checksums.mjs
@@ -0,0 +1,48 @@
+#!/usr/bin/env node
+// Writes checksums.json for one release version. Run from prepublishOnly, after the
+// GitHub release for `v<version>` exists.
+//
+// It downloads every platform binary and hashes the bytes. It also checks each hash
+// against the release's `.sha256` sidecar, so a mismatch fails the publish instead of
+// pinning a bad value.
+
+import { createHash } from "node:crypto";
+import { writeFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { fetchSha256, fetchUrl, releaseAssetUrl } from "../lib/download.mjs";
+import { allAssetNames } from "../lib/platform.mjs";
+
+export async function pinChecksums(
+  version,
+  { out, fetchBinary = fetchUrl, fetchSidecar = fetchSha256 } = {},
+) {
+  const assets = {};
+  for (const assetName of allAssetNames()) {
+    const bytes = await fetchBinary(releaseAssetUrl(version, assetName));
+    const actual = createHash("sha256").update(bytes).digest("hex");
+    const sidecar = await fetchSidecar(version, assetName);
+    if (!sidecar) {
+      throw new Error(`No .sha256 sidecar published for ${assetName} in v${version}.`);
+    }
+    if (sidecar.toLowerCase() !== actual) {
+      throw new Error(
+        `Sidecar for ${assetName} does not match the binary (sidecar ${sidecar}, binary ${actual}).`,
+      );
+    }
+    assets[assetName] = actual;
+  }
+  const pinned = { version, assets };
+  if (out) writeFileSync(out, `${JSON.stringify(pinned, null, 2)}\n`);
+  return pinned;
+}
+
+if (process.argv[1] === fileURLToPath(import.meta.url)) {
+  const version = process.argv[2];
+  if (!version || /dev$/.test(version) || version === "0.0.0") {
+    console.error("usage: pin-checksums.mjs <release-version>  (refuses dev versions)");
+    process.exit(1);
+  }
+  const out = fileURLToPath(new URL("../checksums.json", import.meta.url));
+  await pinChecksums(version, { out });
+  console.log(`Pinned ${allAssetNames().length} checksums for v${version} -> checksums.json`);
+}
diff --git a/npm/code-cli/scripts/prepublish.sh b/npm/code-cli/scripts/prepublish.sh
index 9d7026d..4fa16e8 100755
--- a/npm/code-cli/scripts/prepublish.sh
+++ b/npm/code-cli/scripts/prepublish.sh
@@ -18,5 +18,9 @@ for f in bin/index.js lib/platform.mjs lib/resolve-binary.mjs lib/download.mjs s
   fi
 done
 
+# Pin the release binaries' checksums into the package. Requires the GitHub release
+# for v$VERSION to exist, so publish after the release workflow has finished.
+node ./scripts/pin-checksums.mjs "$VERSION"
+
 echo "==> Pre-publish checks passed (v$VERSION). Running tests."
 exec ./scripts/test.sh
diff --git a/npm/code-cli/tests/pinned-checksums.test.mjs b/npm/code-cli/tests/pinned-checksums.test.mjs
new file mode 100644
index 0000000..c2dcf76
--- /dev/null
+++ b/npm/code-cli/tests/pinned-checksums.test.mjs
@@ -0,0 +1,100 @@
+import assert from "node:assert/strict";
+import { createHash } from "node:crypto";
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { test } from "node:test";
+import { downloadRelease } from "../lib/download.mjs";
+import { pinnedSha256 } from "../lib/pinned-checksums.mjs";
+import { allAssetNames, detectTarget } from "../lib/platform.mjs";
+import { pinChecksums } from "../scripts/pin-checksums.mjs";
+
+const sha = (buf) => createHash("sha256").update(buf).digest("hex");
+const VERSION = "9.9.9";
+
+test("pinnedSha256 refuses when no checksums are bundled", () => {
+  assert.throws(() => pinnedSha256(null, VERSION, "code-cli-x"), /No pinned checksums/);
+});
+
+test("pinnedSha256 refuses checksums for a different version", () => {
+  const pinned = { version: "1.0.0", assets: { "code-cli-x": "aa" } };
+  assert.throws(() => pinnedSha256(pinned, VERSION, "code-cli-x"), /are for v1\.0\.0/);
+});
+
+test("pinnedSha256 refuses an asset with no entry and returns a matching one", () => {
+  const pinned = { version: VERSION, assets: { "code-cli-x": "abc" } };
+  assert.equal(pinnedSha256(pinned, VERSION, "code-cli-x"), "abc");
+  assert.throws(() => pinnedSha256(pinned, VERSION, "code-cli-y"), /No pinned SHA-256/);
+});
+
+test("allAssetNames lists every platform asset once", () => {
+  const names = allAssetNames();
+  assert.equal(new Set(names).size, names.length);
+  assert.equal(names.length, 5);
+  assert.ok(names.includes(detectTarget().assetName));
+});
+
+test("downloadRelease refuses a binary that matches its sidecar but not the pinned checksum", async () => {
+  // A release replaced wholesale: the binary and its sidecar agree with each other, but
+  // not with the checksum pinned when the npm package was published.
+  const { assetName } = detectTarget();
+  const tampered = Buffer.from("tampered binary");
+  const realFetch = globalThis.fetch;
+  globalThis.fetch = async (url) =>
+    String(url).endsWith(".sha256")
+      ? new Response(`${sha(tampered)}  ${assetName}`, { status: 200 })
+      : new Response(tampered, { status: 200 });
+  try {
+    const pinned = { version: VERSION, assets: { [assetName]: sha(Buffer.from("genuine")) } };
+    await assert.rejects(
+      downloadRelease({
+        version: VERSION,
+        destDir: mkdtempSync(join(tmpdir(), "fc-pin-")),
+        pinned,
+      }),
+      /does not match the checksum pinned/,
+    );
+  } finally {
+    globalThis.fetch = realFetch;
+  }
+});
+
+test("downloadRelease installs a binary that matches both the sidecar and the pinned checksum", async () => {
+  const { assetName } = detectTarget();
+  const genuine = Buffer.from("genuine binary");
+  const realFetch = globalThis.fetch;
+  globalThis.fetch = async (url) =>
+    String(url).endsWith(".sha256")
+      ? new Response(`${sha(genuine)}  ${assetName}`, { status: 200 })
+      : new Response(genuine, { status: 200 });
+  try {
+    const pinned = { version: VERSION, assets: { [assetName]: sha(genuine) } };
+    const binPath = await downloadRelease({
+      version: VERSION,
+      destDir: mkdtempSync(join(tmpdir(), "fc-pin-")),
+      pinned,
+    });
+    assert.ok(binPath.endsWith(detectTarget().binName));
+  } finally {
+    globalThis.fetch = realFetch;
+  }
+});
+
+test("pinChecksums hashes the binaries and rejects a sidecar that disagrees", async () => {
+  const bytes = Buffer.from("release bytes");
+  const ok = await pinChecksums(VERSION, {
+    fetchBinary: async () => bytes,
+    fetchSidecar: async () => sha(bytes),
+  });
+  assert.equal(ok.version, VERSION);
+  assert.equal(Object.keys(ok.assets).length, allAssetNames().length);
+  for (const hex of Object.values(ok.assets)) assert.equal(hex, sha(bytes));
+
+  await assert.rejects(
+    pinChecksums(VERSION, {
+      fetchBinary: async () => bytes,
+      fetchSidecar: async () => sha(Buffer.from("other")),
+    }),
+    /does not match the binary/,
+  );
+});