fix(zbugs-gpui): mark an issue viewed after the server confirms its changes (#186)

The zbugs GPUI end-to-end job failed once on #185 at the viewState check:
`e2e online: passed`, then Postgres had the issue's viewed time before its
modified time.

zbugs' issue trigger stamps `modified` with the time the server's
transaction for a change starts, after the client showed the change. The
one-second view timer took its viewed time from the client's state, so when
it fired before the server had applied the close, the server's stamp came
later. The app marked the issue viewed again a second after the server
confirmed it, but the run had already exited.

The timer now waits until the server has confirmed the pending mutations
before it takes the viewed time, as `max(now, modified)` of the confirmed
issue.

Amp-Thread-ID: https://ampcode.com/threads/T-5a01d9bf-e8fb-479a-8866-c293f3e230d5

Co-authored-by: Amp <amp@ampcode.com>

Author: tmm

apps/zbugs-gpui/src/app.rs

@@ -9,7 +9,7 @@ use crate::live::Live;
 use crate::picker::{self, Choice};
 use crate::session::{Session, app_dir, now_ms, save_setting};
 use futures::StreamExt;
-use futures::channel::mpsc;
+use futures::channel::{mpsc, oneshot};
 use gpui_kit::assets::IconName as Lucide;
 use gpui_kit::base::actions::Confirm;
 use gpui_kit::component::button::*;
@@ -1407,9 +1407,21 @@ impl ZbugsApp {
             cx.background_executor()
                 .timer(std::time::Duration::from_secs(1))
                 .await;
+            // Then once the server has confirmed what's pending: it stamps
+            // an issue's `modified` itself as it applies a change, after the
+            // client showed it, so a viewed time taken before that would
+            // leave the issue unread.
+            let (done, settled) = oneshot::channel();
+            let waiting = this.update(cx, |this, _| {
+                this.session.zero.when_pending_settled(move || {
+                    let _ = done.send(());
+                })
+            });
+            if waiting.is_err() || settled.await.is_err() {
+                return;
+            }
             let _ = this.update(cx, |this, cx| {
-                // Done: a change the server confirms after this one, such
-                // as its own `modified` for a close, starts another.
+                // Done: a change after this one starts another.
                 this.view_timer = None;
                 let modified = this
                     .detail