don't call onClose in static generation

packages/next/src/server/after/after.ts

@@ -135,9 +135,18 @@ export function createAfterContext({
           : callback())
 
         // NOTE: if the callback returns a stream, there may still be components that'll execute later,
-        // which means that more callbacks can be added.
-        // TODO: can we call onClose lazily?
-        onClose(() => runCallbacks(requestStore))
+        // which means that more callbacks can be added after this point.
+
+        // `onClose` is not available in static generation.
+        // after() calls will throw and bail out anyway, but streaming can make them happen later,
+        // so we don't want to crash here.
+        const hasOnClose =
+          !staticGenerationAsyncStorage.getStore()?.isStaticGeneration
+
+        if (hasOnClose) {
+          // TODO: can we call onClose lazily somehow?
+          onClose(() => runCallbacks(requestStore))
+        }
         return res
       } finally {
         // if something failed, make sure the request doesn't stay open forever.