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diff --git a/test-apps/server-component-change-children/src/app.gleam b/test-apps/server-component-change-children/src/app.gleam
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+++ b/test-apps/server-component-change-children/src/app.gleam
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+import counter
+import gleam/bytes_builder
+import gleam/erlang
+import gleam/erlang/process.{type Selector, type Subject}
+import gleam/http/request.{type Request}
+import gleam/http/response.{type Response}
+import gleam/json
+import gleam/option.{type Option, None}
+import gleam/otp/actor
+import gleam/result
+import lustre
+import lustre/attribute
+import lustre/element
+import lustre/element/html.{html}
+import lustre/server_component
+import mist.{
+  type Connection, type ResponseData, type WebsocketConnection,
+  type WebsocketMessage,
+}
+
+pub fn main() {
+  let assert Ok(_) =
+    fn(req: Request(Connection)) -> Response(ResponseData) {
+      case request.path_segments(req) {
+        // Set up the websocket connection to the client. This is how we send
+        // DOM updates to the browser and receive events from the client.
+        ["counter"] ->
+          mist.websocket(
+            request: req,
+            on_init: socket_init,
+            on_close: socket_close,
+            handler: socket_update,
+          )
+
+        // We need to serve the server component runtime. There's also a minified
+        // version of this script for production.
+        ["lustre-server-component.mjs"] -> {
+          let assert Ok(priv) = erlang.priv_directory("lustre")
+          let path = priv <> "/static/lustre-server-component.mjs"
+
+          mist.send_file(path, offset: 0, limit: None)
+          |> result.map(fn(script) {
+            response.new(200)
+            |> response.prepend_header("content-type", "application/javascript")
+            |> response.set_body(script)
+          })
+          |> result.lazy_unwrap(fn() {
+            response.new(404)
+            |> response.set_body(mist.Bytes(bytes_builder.new()))
+          })
+        }
+
+        // For all other requests we'll just serve some HTML that renders the
+        // server component.
+        _ ->
+          response.new(200)
+          |> response.prepend_header("content-type", "text/html")
+          |> response.set_body(
+            html([], [
+              html.head([], [
+                html.link([
+                  attribute.rel("stylesheet"),
+                  attribute.href(
+                    "https://cdn.jsdelivr.net/gh/lustre-labs/ui/priv/styles.css",
+                  ),
+                ]),
+                html.script(
+                  [
+                    attribute.type_("module"),
+                    attribute.src("/lustre-server-component.mjs"),
+                  ],
+                  "",
+                ),
+              ]),
+              html.body([], [
+                server_component.component([server_component.route("/counter")]),
+              ]),
+            ])
+            |> element.to_document_string_builder
+            |> bytes_builder.from_string_builder
+            |> mist.Bytes,
+          )
+      }
+    }
+    |> mist.new
+    |> mist.port(3000)
+    |> mist.start_http
+
+  process.sleep_forever()
+}
+
+//
+
+type Counter =
+  Subject(lustre.Action(counter.Msg, lustre.ServerComponent))
+
+fn socket_init(
+  conn: WebsocketConnection,
+) -> #(Counter, Option(Selector(lustre.Patch(counter.Msg)))) {
+  let app = counter.app()
+  let assert Ok(counter) = lustre.start_actor(app, 0)
+
+  process.send(
+    counter,
+    server_component.subscribe(
+      // server components can have many connected clients, so we need a way to
+      // identify this client.
+      "ws",
+      // this callback is called whenever the server component has a new patch
+      // to send to the client. here we json encode that patch and send it to
+      // via the websocket connection.
+      //
+      // a more involved version would have us sending the patch to this socket's
+      // subject, and then it could be handled (perhaps with some other work) in
+      // the `mist.Custom` branch of `socket_update` below.
+      fn(patch) {
+        let assert Ok(_) =
+          patch
+          |> server_component.encode_patch
+          |> json.to_string
+          |> mist.send_text_frame(conn, _)
+
+        Nil
+      },
+    ),
+  )
+
+  #(
+    // we store the server component's `Subject` as this socket's state so we
+    // can shut it down when the socket is closed.
+    counter,
+    // the `None` here means we aren't planning on receiving any messages from
+    // elsewhere and dont need a `Selector` to handle them.
+    None,
+  )
+}
+
+import gleam/io
+
+fn socket_update(
+  counter: Counter,
+  _conn: WebsocketConnection,
+  msg: WebsocketMessage(lustre.Patch(counter.Msg)),
+) {
+  case msg {
+    mist.Text(json) -> {
+      // we attempt to decode the incoming text as an action to send to our
+      // server component runtime.
+      let action = json.decode(json, server_component.decode_action)
+
+      case action {
+        Ok(action) -> process.send(counter, action)
+        Error(_) -> Nil
+      }
+
+      actor.continue(counter)
+    }
+
+    mist.Binary(_) -> actor.continue(counter)
+    mist.Custom(_) -> actor.continue(counter)
+    mist.Closed | mist.Shutdown -> actor.Stop(process.Normal)
+  }
+}
+
+fn socket_close(counter: Counter) {
+  process.send(counter, lustre.shutdown())
+}