include build number in error screen

build.js

@@ -1,6 +1,7 @@
 import { rimraf } from 'rimraf';
 import { copyFile, mkdir, readFile, writeFile } from 'node:fs/promises';
 import { build } from 'esbuild';
+import { execSync } from "node:child_process";
 
 // read version from package.json
 const pkg = JSON.parse(await readFile('package.json'));
@@ -29,6 +30,19 @@ let builder = await build({
         'process.env.ULTRAVIOLET_VERSION': JSON.stringify(
             process.env.ULTRAVIOLET_VERSION
         ),
+        'process.env.ULTRAVIOLET_COMMIT_HASH': (() => {
+			try {
+				let hash = JSON.stringify(
+					execSync("git rev-parse --short HEAD", {
+						encoding: "utf-8",
+					}).replace(/\r?\n|\r/g, "")
+				);
+
+				return hash;
+			} catch (e) {
+				return "unknown";
+			}
+		})(),
     },
     bundle: true,
     treeShaking: true,

src/uv.sw.js

@@ -442,6 +442,9 @@ function errorTemplate(
         uvVersion.textContent = ${JSON.stringify(
             process.env.ULTRAVIOLET_VERSION
         )};
+        uvBuild.textContent = ${JSON.stringify(
+            process.env.ULTRAVIOLET_COMMIT_HASH
+        )};
     `
 
     return (
@@ -476,7 +479,7 @@ function errorTemplate(
         </ul>
         <button id="reload">Reload</button>
         <hr />
-        <p><i>Ultraviolet v<span id="uvVersion"></span></i></p>
+        <p><i>Ultraviolet v<span id="uvVersion"></span> (build <span id="uvBuild"></span>)</i></p>
         <script src="${
             'data:application/javascript,' + encodeURIComponent(script)
         }"></script>