diff --git a/.github/scripts/set-release-version.mjs b/.github/scripts/set-release-version.mjs
new file mode 100644
index 000000000..0559e611b
--- /dev/null
+++ b/.github/scripts/set-release-version.mjs
@@ -0,0 +1,66 @@
+#!/usr/bin/env node
+// Sets the release version in package.json AND package-lock.json.
+//
+// prerelease.yml and promote.yml used to `sed` package.json alone, so every
+// release shipped a lockfile whose root version disagreed with the package it
+// locks:
+//
+//   v1.7.0  package.json=1.7.0  lock=1.6.0
+//   v1.8.0  package.json=1.8.0  lock=1.8.0-rc.4
+//   v1.9.0  package.json=1.9.0  lock=1.8.0
+//
+// Nothing caught it for three releases because `npm ci` only fails on
+// dependency drift, never on this field — the mismatch is inert until someone
+// reads the diff, which is how it was eventually noticed.
+//
+// Both files are tab-indented JSON that JSON.stringify round-trips byte for
+// byte, so rewriting them whole still produces a one-line-per-file diff. The
+// test pins that: if npm ever changes how it formats a lockfile, a release
+// commit would otherwise silently become a 40k-line reformat.
+
+import { readFileSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { argv } from "node:process";
+
+/**
+ * @param {string} version Version to write, e.g. "1.9.0" or "1.9.0-rc.2".
+ * @param {string} dir Directory holding package.json and package-lock.json.
+ */
+export function setReleaseVersion(version, dir) {
+	if (!version) throw new Error("a version is required");
+
+	const edit = (name, mutate) => {
+		const file = join(dir, name);
+		const json = JSON.parse(readFileSync(file, "utf8"));
+		mutate(json);
+		writeFileSync(file, `${JSON.stringify(json, null, "\t")}\n`);
+	};
+
+	edit("package.json", (pkg) => {
+		pkg.version = version;
+	});
+
+	edit("package-lock.json", (lock) => {
+		lock.version = version;
+		// lockfileVersion 3 repeats the root version inside packages[""]. Optional
+		// chaining would quietly skip it if the shape ever changed — the same
+		// silent half-bump this script exists to end — so demand it instead.
+		if (!lock.packages?.[""]) {
+			throw new Error(
+				'package-lock.json has no packages[""] entry; the lockfile format changed and this script needs updating',
+			);
+		}
+		lock.packages[""].version = version;
+	});
+}
+
+// Only run when invoked directly, so the test can import the function.
+if (import.meta.filename === argv[1]) {
+	const version = argv[2];
+	if (!version) {
+		console.error("usage: node .github/scripts/set-release-version.mjs <version>");
+		process.exit(1);
+	}
+	setReleaseVersion(version, process.cwd());
+	console.log(`version ${version} set in package.json and package-lock.json`);
+}
diff --git a/.github/scripts/set-release-version.test.mjs b/.github/scripts/set-release-version.test.mjs
new file mode 100644
index 000000000..baf80a8cb
--- /dev/null
+++ b/.github/scripts/set-release-version.test.mjs
@@ -0,0 +1,115 @@
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { setReleaseVersion } from "./set-release-version.mjs";
+
+let dir;
+
+// Tab-indented, like the real files, and shaped like lockfileVersion 3 — the
+// point of most of these assertions is formatting, so the fixtures have to be
+// byte-faithful rather than merely structurally right.
+const pkg = [
+	"{",
+	'\t"name": "openscreen",',
+	'\t"version": "1.8.0",',
+	'\t"private": true',
+	"}",
+	"",
+].join("\n");
+
+const lock = [
+	"{",
+	'\t"name": "openscreen",',
+	'\t"version": "1.8.0",',
+	'\t"lockfileVersion": 3,',
+	'\t"requires": true,',
+	'\t"packages": {',
+	'\t\t"": {',
+	'\t\t\t"name": "openscreen",',
+	'\t\t\t"version": "1.8.0",',
+	'\t\t\t"dependencies": {',
+	'\t\t\t\t"zod": "^4.0.0"',
+	"\t\t\t}",
+	"\t\t},",
+	'\t\t"node_modules/zod": {',
+	'\t\t\t"version": "4.0.0"',
+	"\t\t}",
+	"\t}",
+	"}",
+	"",
+].join("\n");
+
+beforeEach(() => {
+	dir = mkdtempSync(join(tmpdir(), "set-release-version-"));
+	writeFileSync(join(dir, "package.json"), pkg);
+	writeFileSync(join(dir, "package-lock.json"), lock);
+});
+
+afterEach(() => {
+	rmSync(dir, { recursive: true, force: true });
+});
+
+const read = (name) => readFileSync(join(dir, name), "utf8");
+
+describe("setReleaseVersion", () => {
+	it("sets the version in package.json and both lockfile roots", () => {
+		setReleaseVersion("1.9.0", dir);
+
+		expect(JSON.parse(read("package.json")).version).toBe("1.9.0");
+		const written = JSON.parse(read("package-lock.json"));
+		expect(written.version).toBe("1.9.0");
+		expect(written.packages[""].version).toBe("1.9.0");
+	});
+
+	it("accepts a prerelease version", () => {
+		setReleaseVersion("2.0.0-rc.3", dir);
+
+		expect(JSON.parse(read("package.json")).version).toBe("2.0.0-rc.3");
+		expect(JSON.parse(read("package-lock.json")).packages[""].version).toBe("2.0.0-rc.3");
+	});
+
+	// The reason the script may rewrite these files wholesale: anything else in
+	// them must come back out byte for byte. If npm changes its lockfile
+	// formatting, this fails here rather than turning a release commit into a
+	// 40k-line reformat nobody reviews.
+	it("changes only the version lines, leaving formatting untouched", () => {
+		setReleaseVersion("1.9.0", dir);
+
+		const diff = (before, after) => {
+			const a = before.split("\n");
+			const b = after.split("\n");
+			expect(b.length).toBe(a.length);
+			return a.map((line, i) => [line, b[i]]).filter(([x, y]) => x !== y);
+		};
+
+		expect(diff(pkg, read("package.json"))).toEqual([
+			['\t"version": "1.8.0",', '\t"version": "1.9.0",'],
+		]);
+		expect(diff(lock, read("package-lock.json"))).toEqual([
+			['\t"version": "1.8.0",', '\t"version": "1.9.0",'],
+			['\t\t\t"version": "1.8.0",', '\t\t\t"version": "1.9.0",'],
+		]);
+	});
+
+	it("leaves dependency versions alone", () => {
+		setReleaseVersion("1.9.0", dir);
+
+		const written = JSON.parse(read("package-lock.json"));
+		expect(written.packages["node_modules/zod"].version).toBe("4.0.0");
+	});
+
+	// A lockfile format change must stop the release, not half-bump it.
+	it("throws rather than half-bumping when the lockfile shape is unknown", () => {
+		writeFileSync(
+			join(dir, "package-lock.json"),
+			`${JSON.stringify({ name: "openscreen", version: "1.8.0" }, null, "\t")}\n`,
+		);
+
+		expect(() => setReleaseVersion("1.9.0", dir)).toThrow(/packages/);
+	});
+
+	it("requires a version", () => {
+		expect(() => setReleaseVersion("", dir)).toThrow(/version is required/);
+	});
+});
diff --git a/.github/workflows/prerelease.yml b/.github/workflows/prerelease.yml
index 8723005fe..5a3e1c56d 100644
--- a/.github/workflows/prerelease.yml
+++ b/.github/workflows/prerelease.yml
@@ -106,10 +106,10 @@ jobs:
             echo "Creating release branch ${BRANCH} from ${GITHUB_REF_NAME}"
             git checkout -b "$BRANCH"
           fi
-          sed -i -E "s|(\"version\"[[:space:]]*:[[:space:]]*\")[^\"]*(\")|\1${PRERELEASE}\2|" package.json
-          echo "package.json version:"
-          grep '"version"' package.json
-          git add package.json
+          # Writes package-lock.json too. A sed over package.json alone left the
+          # lockfile behind on every release up to 1.9.0; see the script header.
+          node .github/scripts/set-release-version.mjs "${PRERELEASE}"
+          git add package.json package-lock.json
           git commit -m "chore(release): bump to ${PRERELEASE} [skip ci]" || echo "(version already at ${PRERELEASE})"
           git push "$REMOTE" "$BRANCH"
 
diff --git a/.github/workflows/promote.yml b/.github/workflows/promote.yml
index 3e8214b9c..ce52a242e 100644
--- a/.github/workflows/promote.yml
+++ b/.github/workflows/promote.yml
@@ -59,25 +59,25 @@ jobs:
           STABLE_VERSION: ${{ steps.version.outputs.stable_version }}
         run: node .github/scripts/release-milestone-close.mjs
 
-      - name: Bump package.json to stable version on the release branch
+      - name: Bump the version to stable on the release branch
         env:
           TOKEN: ${{ secrets.OPENSCREEN_RELEASE_TOKEN }}
           STABLE_VERSION: ${{ steps.version.outputs.stable_version }}
         run: |
           set -euo pipefail
           # Promote checks out the FROZEN release branch (created by prerelease.yml) and
-          # rewrites package.json there. This guarantees the stable tag points at the
+          # rewrites the version there. This guarantees the stable tag points at the
           # same code that was tested as the RC plus any cherry-picked bugfixes.
           BRANCH="release/v${STABLE_VERSION}"
           git fetch origin "$BRANCH"
           git checkout "$BRANCH"
           git reset --hard "origin/${BRANCH}"
-          sed -i -E "s|(\"version\"[[:space:]]*:[[:space:]]*\")[^\"]*(\")|\1${STABLE_VERSION}\2|" package.json
-          echo "package.json version:"
-          grep '"version"' package.json
+          # Writes package-lock.json too. A sed over package.json alone left the
+          # lockfile behind on every release up to 1.9.0; see the script header.
+          node .github/scripts/set-release-version.mjs "${STABLE_VERSION}"
           git config user.name  "github-actions[bot]"
           git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
-          git add package.json
+          git add package.json package-lock.json
           git commit --allow-empty -m "chore(release): bump to ${STABLE_VERSION} [skip ci]" || true
           git push "https://x-access-token:${TOKEN}@github.com/${GITHUB_REPOSITORY}.git" "$BRANCH"