Fix incremental build fingerprint invalidation

tools/web/web-build-fingerprint.mjs

@@ -32,12 +32,15 @@ export function inputFiles() {
 export function fingerprint() {
   const hash = crypto.createHash("sha256");
   for (const file of inputFiles()) {
-    const stat = fs.statSync(file);
+    // Read nanosecond metadata as bigint. Without the explicit option
+    // `mtimeNs` is undefined in Node, so same-sized edits can reuse stale
+    // bundles indefinitely.
+    const stat = fs.statSync(file, { bigint: true });
     hash.update(path.relative(root, file));
     hash.update("\0");
-    hash.update(String(stat.size));
+    hash.update(stat.size.toString());
     hash.update("\0");
-    hash.update(String(stat.mtimeNs));
+    hash.update(stat.mtimeNs.toString());
     hash.update("\n");
   }
   return hash.digest("hex");