From e6fa5289f2de03bc7babf2ec07efef6b45ed398f Mon Sep 17 00:00:00 2001
From: akbash <akbash@herdr.dev>
Date: Tue, 4 Aug 2026 15:37:33 +0300
Subject: fix(ui): preserve sidebar scroll across clients (#2280)

refs #2255

Co-authored-by: akbash-bot <300245827+akbash-bot@users.noreply.github.com>
---
 tests/multi_client.rs | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

(limited to 'tests')

diff --git a/tests/multi_client.rs b/tests/multi_client.rs
index 6e367eaf..20deedaf 100644
--- a/tests/multi_client.rs
+++ b/tests/multi_client.rs
@@ -273,6 +273,19 @@ fn create_workspace_and_root_pane(socket_path: &Path, label: &str) -> (String, S
     (workspace_id, pane_id)
 }
 
+fn report_idle_agent(socket_path: &Path, pane_id: &str) {
+    let response = send_json_request(
+        socket_path,
+        &format!(
+            r#"{{"id":"report_agent","method":"pane.report_agent","params":{{"pane_id":"{pane_id}","agent":"pi","state":"idle","source":"multi-client-test"}}}}"#
+        ),
+    );
+    assert!(
+        response.get("error").is_none(),
+        "pane.report_agent should succeed: {response}"
+    );
+}
+
 fn pane_send_input(socket_path: &Path, pane_id: &str, text: &str) {
     let request = format!(
         "{{\"id\":\"send_input\",\"method\":\"pane.send_input\",\"params\":{{\"pane_id\":\"{pane_id}\",\"text\":\"{}\",\"keys\":[\"Enter\"]}}}}",
@@ -747,6 +760,15 @@ fn frame_contains_text(frame: &FrameWire, needle: &str) -> bool {
     frame_text(frame).contains(needle)
 }
 
+fn agent_panel_starts_with(frame: &FrameWire, agent_label: &str) -> bool {
+    frame_text(frame)
+        .lines()
+        .skip_while(|line| !line.contains("agents"))
+        .skip(1)
+        .find(|line| line.contains("agent-"))
+        .is_some_and(|line| line.contains(agent_label))
+}
+
 #[test]
 fn multi_client_allows_multiple_simultaneous_connections() {
     let _lock = test_lock();
@@ -827,6 +849,75 @@ fn multi_client_effective_size_shrinks_when_smaller_client_joins() {
     cleanup_spawned_herdr(server, base);
 }
 
+#[test]
+fn non_foreground_client_render_preserves_agent_panel_scroll() {
+    let _lock = test_lock();
+    let base = unique_test_dir();
+    let config_home = base.join("config");
+    let runtime_dir = base.join("runtime");
+    let api_socket = runtime_dir.join("herdr.sock");
+    let client_socket = runtime_dir.join("herdr-client.sock");
+
+    let server = spawn_server(&config_home, &runtime_dir, &api_socket);
+    wait_for_socket(&api_socket, Duration::from_secs(10));
+    wait_for_file(&client_socket, Duration::from_secs(10));
+
+    for index in 1..=23 {
+        let (_, pane_id) =
+            create_workspace_and_root_pane(&api_socket, &format!("agent-{index:02}"));
+        report_idle_agent(&api_socket, &pane_id);
+    }
+
+    let mut setup_client = connect_raw_client(&client_socket, 106, 40);
+    assert!(wait_for_frame(&mut setup_client, Duration::from_secs(2)));
+    drain_server_messages(&mut setup_client, Duration::from_millis(250));
+
+    let wheel_down = b"\x1b[<65;10;30M";
+    send_client_input(&mut setup_client, &wheel_down.repeat(20));
+    let (reached_bottom, setup_frames) = wait_for_frame_matching_with_snapshots(
+        &mut setup_client,
+        Duration::from_secs(3),
+        |frame| agent_panel_starts_with(frame, "agent-16"),
+    )
+    .expect("setup frame decoding should succeed");
+    assert!(
+        reached_bottom,
+        "40-row client should scroll the agent panel to its final page; frames:\n{}",
+        setup_frames.join("\n--- frame ---\n")
+    );
+    send_client_detach(&mut setup_client);
+    drop(setup_client);
+
+    let mut tall_background = connect_raw_client(&client_socket, 106, 64);
+    assert!(wait_for_frame(&mut tall_background, Duration::from_secs(2)));
+    let mut probe = connect_raw_client(&client_socket, 106, 40);
+    let (started_at_tall_limit, initial_frames) =
+        wait_for_frame_matching_with_snapshots(&mut probe, Duration::from_secs(3), |frame| {
+            agent_panel_starts_with(frame, "agent-10")
+        })
+        .expect("initial probe frame decoding should succeed");
+    assert!(
+        started_at_tall_limit,
+        "tall client should normalize the shared scroll before the probe attaches; frames:\n{}",
+        initial_frames.join("\n--- frame ---\n")
+    );
+    drain_server_messages(&mut probe, Duration::from_millis(250));
+
+    send_client_input(&mut probe, wheel_down);
+    let (scrolled, probe_frames) =
+        wait_for_frame_matching_with_snapshots(&mut probe, Duration::from_secs(3), |frame| {
+            agent_panel_starts_with(frame, "agent-11")
+        })
+        .expect("probe frame decoding should succeed");
+    assert!(
+        scrolled,
+        "background client projection must not undo the foreground wheel event; frames:\n{}",
+        probe_frames.join("\n--- frame ---\n")
+    );
+
+    cleanup_spawned_herdr(server, base);
+}
+
 #[test]
 fn multi_client_broadcasts_frame_updates_to_all_clients() {
     let _lock = test_lock();
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