From 159f509dd606851d6bfd53617680a0db598eea86 Mon Sep 17 00:00:00 2001
From: Hunter B <hmbown@gmail.com>
Date: Wed, 3 Jun 2026 19:38:19 -0700
Subject: [PATCH] fix(tui): invalidate fanout card rows on sibling starts

---
 crates/tui/src/tui/subagent_routing.rs |  2 ++
 crates/tui/src/tui/ui/tests.rs         | 41 +++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/crates/tui/src/tui/subagent_routing.rs b/crates/tui/src/tui/subagent_routing.rs
index 318203b2..60168d1b 100644
--- a/crates/tui/src/tui/subagent_routing.rs
+++ b/crates/tui/src/tui/subagent_routing.rs
@@ -155,6 +155,7 @@ pub(super) fn handle_subagent_mailbox(app: &mut App, seq: u64, message: &Mailbox
         {
             card.claim_pending_worker(&agent_id, AgentLifecycle::Running);
             app.subagent_card_index.insert(agent_id, idx);
+            app.bump_history_cell(idx);
         } else {
             let mut card = FanoutCard::new(
                 dispatch_kind.unwrap_or("rlm_eval").to_string(),
@@ -165,6 +166,7 @@ pub(super) fn handle_subagent_mailbox(app: &mut App, seq: u64, message: &Mailbox
             let idx = app.history.len().saturating_sub(1);
             app.last_fanout_card_index = Some(idx);
             app.subagent_card_index.insert(agent_id, idx);
+            app.bump_history_cell(idx);
         }
     } else {
         let card = DelegateCard::new(agent_id.clone(), agent_type.clone());
diff --git a/crates/tui/src/tui/ui/tests.rs b/crates/tui/src/tui/ui/tests.rs
index 5c916fdd..38d3c650 100644
--- a/crates/tui/src/tui/ui/tests.rs
+++ b/crates/tui/src/tui/ui/tests.rs
@@ -18,7 +18,7 @@ use crate::tui::footer_ui::{
     friendly_subagent_progress, render_footer_from,
 };
 use crate::tui::history::{
-    ExecCell, ExecSource, GenericToolCell, HistoryCell, ToolCell, ToolStatus,
+    ExecCell, ExecSource, GenericToolCell, HistoryCell, SubAgentCell, ToolCell, ToolStatus,
 };
 use crate::tui::views::{ModalView, ViewAction};
 use crate::working_set::Workspace;
@@ -3254,6 +3254,45 @@ fn subagent_token_usage_is_deduped_by_mailbox_sequence() {
     assert!(app.session.subagent_cost > first);
 }
 
+#[test]
+fn fanout_started_sibling_bumps_existing_card_revision() {
+    let mut app = create_test_app();
+    app.pending_subagent_dispatch = Some("rlm".to_string());
+
+    handle_subagent_mailbox(
+        &mut app,
+        1,
+        &crate::tools::subagent::MailboxMessage::Started {
+            agent_id: "fanout-a".to_string(),
+            agent_type: "default".to_string(),
+        },
+    );
+
+    let fanout_idx = app.last_fanout_card_index.expect("fanout card index");
+    let initial_revision = app.history_revisions[fanout_idx];
+
+    handle_subagent_mailbox(
+        &mut app,
+        2,
+        &crate::tools::subagent::MailboxMessage::Started {
+            agent_id: "fanout-b".to_string(),
+            agent_type: "default".to_string(),
+        },
+    );
+
+    assert_eq!(app.history.len(), 1, "sibling should reuse fanout card");
+    assert_ne!(
+        app.history_revisions[fanout_idx], initial_revision,
+        "reused fanout card must invalidate its cached transcript rows"
+    );
+    match &app.history[fanout_idx] {
+        HistoryCell::SubAgent(SubAgentCell::Fanout(card)) => {
+            assert_eq!(card.worker_count(), 2);
+        }
+        cell => panic!("expected fanout card, got {cell:?}"),
+    }
+}
+
 #[test]
 fn format_token_count_compact_formats_units() {
     assert_eq!(format_token_count_compact(999), "999");