Prevent duplicate command monitor timers

app/src/terminal/view.rs

@@ -734,6 +734,13 @@ const COMMAND_AUTO_MONITOR_DELAY: Duration = Duration::from_secs(3);
 const COMMAND_MONITOR_RETRY_INTERVAL: Duration = Duration::from_millis(500);
 const COMMAND_MONITOR_FORCE_REFRESH_RETRIES: u8 = 20;
 
+fn register_command_monitor_start(
+    pending_starts: &mut HashSet<BlockId>,
+    block_id: &BlockId,
+) -> bool {
+    pending_starts.insert(block_id.clone())
+}
+
 #[derive(Default)]
 pub struct ControlMasterErrorBannerState {
     /// Whether or not the control master error banner is currently visible to
@@ -2668,6 +2675,10 @@ pub struct TerminalView {
     /// long-running threshold. Reset when the active command starts and finishes.
     did_notify_long_running: bool,
 
+    /// Blocks with an automatic monitor-start timer already scheduled. Keeping this registry on
+    /// the terminal view prevents duplicate command-start events from creating competing timers.
+    pending_command_monitor_starts: HashSet<BlockId>,
+
     /// This field is an "&&" combination of two other pieces of state:
     ///   1. Whether this View (or one of its children) is the focused View.
     ///   2. Whether this View's window is the active window.
@@ -4347,6 +4358,7 @@ impl TerminalView {
             view_id: ctx.view_id(),
             current_state: TerminalViewStateChange::default(),
             did_notify_long_running: false,
+            pending_command_monitor_starts: HashSet::new(),
             is_focused_and_active: true,
             current_prompt,
             model_event_sender,
@@ -6646,6 +6658,7 @@ impl TerminalView {
                 conversation_id,
                 initial_requested_command_action_id,
             } => {
+                self.pending_command_monitor_starts.remove(block_id);
                 let subagent_view = ctx.add_typed_action_view(|ctx| {
                     CLISubagentView::new(
                         block_id.clone(),
@@ -6755,6 +6768,7 @@ impl TerminalView {
                 conversation_id,
                 ..
             } => {
+                self.pending_command_monitor_starts.remove(block_id);
                 self.cli_subagent_views.remove(block_id);
 
                 // The command ended — drop any LRC-scoped auto-queue override so the
@@ -7398,6 +7412,10 @@ impl TerminalView {
     }
 
     fn schedule_command_monitor_start(&mut self, block_id: BlockId, ctx: &mut ViewContext<Self>) {
+        if !register_command_monitor_start(&mut self.pending_command_monitor_starts, &block_id) {
+            return;
+        }
+
         self.schedule_command_monitor_start_after(
             block_id,
             COMMAND_AUTO_MONITOR_DELAY,
@@ -7439,10 +7457,13 @@ impl TerminalView {
                         ctx,
                     );
                 } else if waiting_for_threshold {
+                    me.pending_command_monitor_starts.remove(&block_id);
                     log::warn!(
                         "Command block {block_id:?} never reached the long-running threshold; \
                              automatic command monitoring was not started"
                     );
+                } else {
+                    me.pending_command_monitor_starts.remove(&block_id);
                 }
                 return;
             }
@@ -7463,6 +7484,7 @@ impl TerminalView {
                     ctx,
                 );
             } else {
+                me.pending_command_monitor_starts.remove(&block_id);
                 log::warn!(
                     "Could not find the pending shell action for long-running block \
                          {block_id:?}; automatic command monitoring was not started"
@@ -11719,6 +11741,7 @@ impl TerminalView {
                 ctx.request_user_attention();
             }
             ModelEvent::Exit { reason } => {
+                self.pending_command_monitor_starts.clear();
                 if !self.manual_pty_shutdown_requested {
                     if let Some(conversation_id) = self.maybe_send_agent_exited_shell_telemetry(ctx)
                     {
@@ -11764,6 +11787,8 @@ impl TerminalView {
                 }
             }
             ModelEvent::BlockCompleted(block_completed_event) => {
+                self.pending_command_monitor_starts
+                    .remove(&block_completed_event.block_id);
                 record_trace_event!("command_execution:block_completed");
                 end_trace_after_next!("window:redraw:end");
                 let block_completed_event_clone = block_completed_event.clone();

app/src/terminal/view_tests.rs

@@ -106,6 +106,27 @@ fn has_pending_user_query_block(view: &TerminalView) -> bool {
     })
 }
 
+#[test]
+fn automatic_command_monitor_start_is_deduplicated_per_block() {
+    let mut pending_starts = HashSet::new();
+    let block_id = BlockId::new();
+
+    assert!(super::register_command_monitor_start(
+        &mut pending_starts,
+        &block_id
+    ));
+    assert!(!super::register_command_monitor_start(
+        &mut pending_starts,
+        &block_id
+    ));
+
+    pending_starts.remove(&block_id);
+    assert!(super::register_command_monitor_start(
+        &mut pending_starts,
+        &block_id
+    ));
+}
+
 #[test]
 fn agent_view_lifecycle_updates_input_mode() {
     App::test((), |mut app| async move {

plans/long-running-command-side-agent.md

@@ -168,11 +168,12 @@ Files:
 
 Tasks:
 
-- Add a terminal-view-scoped monitor registry keyed by command/block ID.
+- [x] Add a terminal-view-scoped monitor registry keyed by command/block ID.
 - Replace the current one-off delayed input-lock check with a monitor-start event or extend the existing event with a long-running transition.
 - Capture command metadata and snapshots without holding `TerminalModel` locks across async work.
-- Add cancellation/completion cleanup paths.
+- [x] Add cancellation/completion cleanup paths.
-- Add focused unit tests for timer race cases and duplicate monitor prevention.
+- [ ] Add focused unit tests for timer race cases.
+- [x] Add deterministic unit coverage for duplicate monitor registration and cleanup.
 
 ### Phase 3: Side-agent conversation creation