fix: add automatic deployment skew protection

src/lib/deployment-id.test.ts

@@ -0,0 +1,15 @@
+import { execFileSync } from "node:child_process";
+import { describe, expect, it } from "vitest";
+import nextConfig from "../../next.config";
+
+describe("deployment version skew protection", () => {
+	it("uses an explicit deployment ID or the current Git commit", () => {
+		const gitCommit = execFileSync("git", ["rev-parse", "HEAD"], {
+			encoding: "utf8",
+		}).trim();
+
+		expect(nextConfig.deploymentId).toBe(
+			process.env.NEXT_DEPLOYMENT_ID?.trim() || gitCommit,
+		);
+	});
+});