fix(tui): hide empty reasoning summaries (#31652)

## Why

Reasoning summaries can contain an empty HTML comment placeholder, `<!--
-->`, when a generated summary part has no prose. The TUI treated that
placeholder as visible summary content, so it leaked into both the
completed conversation history and persisted transcript. Multi-part
empty summaries could also leave later generated status headings visible
as orphaned transcript content.

## What

- Strip the empty reasoning-summary placeholder at the shared
`ReasoningSummaryCell` boundary.
- Suppress the cell when removing placeholders leaves only generated
bold status headings.
- Cover the multi-part placeholder-only shape with a rendering
regression test for both normal history and transcript output.

## How to Test

1. Start Codex TUI with reasoning summaries visible, for example with
`hide_agent_reasoning = false` and `model_reasoning_summary =
"detailed"`.
2. Run a turn that receives an empty generated reasoning-summary part.
3. Confirm that the in-progress status heading may appear while the turn
is running, but the completed history and transcript contain neither
literal `<!-- -->` tokens nor orphaned reasoning headings.
4. Confirm that a reasoning summary with actual prose still renders
normally.

The model output is nondeterministic, so the targeted regression covers
the exact multi-part placeholder shape from the report:

- `just test -p codex-tui
reasoning_summary_block_hides_empty_html_comment_parts`

codex-rs/tui/src/chatwidget.rs

@@ -622,8 +622,8 @@ pub(crate) struct ChatWidget {
     interrupts: InterruptManager,
     // Accumulates the current reasoning block text to extract a header
     reasoning_buffer: String,
-    // Accumulates full reasoning content for transcript-only recording
-    full_reasoning_buffer: String,
+    // Preserves reasoning-summary part boundaries for transcript-only recording.
+    reasoning_summary_parts: Vec<String>,
     status_state: StatusState,
     review: ReviewState,
     // Active hook runs render in a dedicated live cell so they can run alongside tools.

codex-rs/tui/src/chatwidget/constructor.rs

@@ -176,7 +176,7 @@ impl ChatWidget {
             newly_installed_marketplace_tab_id: None,
             interrupts: InterruptManager::new(),
             reasoning_buffer: String::new(),
-            full_reasoning_buffer: String::new(),
+            reasoning_summary_parts: Vec::new(),
             status_state: StatusState::default(),
             review: ReviewState::default(),
             active_hook_cell: None,

codex-rs/tui/src/chatwidget/input_flow.rs

@@ -37,7 +37,7 @@ impl ChatWidget {
                     // Submitted is emitted when user submits.
                     // Reset any reasoning header only when we are actually submitting a turn.
                     self.reasoning_buffer.clear();
-                    self.full_reasoning_buffer.clear();
+                    self.reasoning_summary_parts.clear();
                     self.set_status_header(String::from("Working"));
                     self.submit_user_message(user_message);
                 } else {

codex-rs/tui/src/chatwidget/replay.rs

@@ -113,13 +113,18 @@ impl ChatWidget {
                 summary, content, ..
             } => {
                 if from_replay {
-                    for delta in summary {
-                        self.on_agent_reasoning_delta(delta);
-                    }
-                    if self.config.show_raw_agent_reasoning {
-                        for delta in content {
-                            self.on_agent_reasoning_delta(delta);
+                    let reasoning_parts = summary.into_iter().chain(
+                        self.config
+                            .show_raw_agent_reasoning
+                            .then_some(content)
+                            .into_iter()
+                            .flatten(),
+                    );
+                    for (index, delta) in reasoning_parts.enumerate() {
+                        if index > 0 {
+                            self.on_reasoning_section_break();
                         }
+                        self.on_agent_reasoning_delta(delta);
                     }
                 }
                 self.on_agent_reasoning_final();

codex-rs/tui/src/chatwidget/slash_dispatch.rs

@@ -735,7 +735,7 @@ impl ChatWidget {
                 );
                 if self.is_session_configured() {
                     self.reasoning_buffer.clear();
-                    self.full_reasoning_buffer.clear();
+                    self.reasoning_summary_parts.clear();
                     self.set_status_header(String::from("Working"));
                     self.submit_user_message(user_message);
                 } else {

codex-rs/tui/src/chatwidget/streaming.rs

@@ -226,24 +226,26 @@ impl ChatWidget {
 
     pub(super) fn on_agent_reasoning_final(&mut self) {
         // At the end of a reasoning block, record transcript-only content.
-        self.full_reasoning_buffer.push_str(&self.reasoning_buffer);
-        if !self.full_reasoning_buffer.is_empty() {
-            let cell = history_cell::new_reasoning_summary_block(
-                self.full_reasoning_buffer.clone(),
-                &self.config.cwd,
-            );
+        if !self.reasoning_buffer.is_empty() {
+            self.reasoning_summary_parts
+                .push(std::mem::take(&mut self.reasoning_buffer));
+        }
+        if !self.reasoning_summary_parts.is_empty() {
+            let reasoning_parts = std::mem::take(&mut self.reasoning_summary_parts);
+            let cell = history_cell::new_reasoning_summary_block(reasoning_parts, &self.config.cwd);
             self.add_boxed_history(cell);
         }
         self.reasoning_buffer.clear();
-        self.full_reasoning_buffer.clear();
+        self.reasoning_summary_parts.clear();
         self.request_redraw();
     }
 
     pub(super) fn on_reasoning_section_break(&mut self) {
         // Start a new reasoning block for header extraction and accumulate transcript.
-        self.full_reasoning_buffer.push_str(&self.reasoning_buffer);
-        self.full_reasoning_buffer.push_str("\n\n");
-        self.reasoning_buffer.clear();
+        if !self.reasoning_buffer.is_empty() {
+            self.reasoning_summary_parts
+                .push(std::mem::take(&mut self.reasoning_buffer));
+        }
     }
 
     pub(super) fn on_stream_error(&mut self, message: String, additional_details: Option<String>) {

codex-rs/tui/src/chatwidget/tests/history_replay.rs

@@ -867,7 +867,7 @@ async fn replayed_thread_closed_notification_does_not_exit_tui() {
 }
 
 #[tokio::test]
-async fn replayed_reasoning_item_hides_raw_reasoning_when_disabled() {
+async fn replayed_reasoning_item_preserves_summary_parts_and_hides_raw_reasoning_when_disabled() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
     chat.config.show_raw_agent_reasoning = false;
     chat.handle_thread_session(crate::session_state::ThreadSessionState {
@@ -897,7 +897,10 @@ async fn replayed_reasoning_item_hides_raw_reasoning_when_disabled() {
     chat.replay_thread_item(
         AppServerThreadItem::Reasoning {
             id: "reasoning-1".to_string(),
-            summary: vec!["Summary only".to_string()],
+            summary: vec![
+                "**Plan**\n\ndone".to_string(),
+                "**Checking tests**\n\n<!-- -->".to_string(),
+            ],
             content: vec!["Raw reasoning".to_string()],
         },
         "turn-1".to_string(),
@@ -910,7 +913,7 @@ async fn replayed_reasoning_item_hides_raw_reasoning_when_disabled() {
         }
         other => panic!("expected InsertHistoryCell, got {other:?}"),
     };
-    assert!(!rendered.trim().is_empty());
+    assert_eq!(rendered, "• done\n");
     assert!(!rendered.contains("Raw reasoning"));
 }
 
@@ -1047,6 +1050,82 @@ async fn live_reasoning_summary_is_not_rendered_twice_when_item_completes() {
     assert_eq!(rendered.matches("Summary only").count(), 1);
 }
 
+#[tokio::test]
+async fn live_reasoning_summary_drops_empty_parts_without_losing_content() {
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    chat.show_welcome_banner = false;
+
+    chat.handle_server_notification(
+        ServerNotification::TurnStarted(TurnStartedNotification {
+            thread_id: "thread-1".to_string(),
+            turn: AppServerTurn {
+                id: "turn-1".to_string(),
+                items_view: codex_app_server_protocol::TurnItemsView::Full,
+                items: Vec::new(),
+                status: AppServerTurnStatus::InProgress,
+                error: None,
+                started_at: Some(0),
+                completed_at: None,
+                duration_ms: None,
+            },
+        }),
+        /*replay_kind*/ None,
+    );
+    let _ = drain_insert_history(&mut rx);
+
+    for (summary_index, delta) in [
+        (0, "**Plan**\n\ndone"),
+        (1, "**Checking tests**\n\n<!-- -->"),
+    ] {
+        chat.handle_server_notification(
+            ServerNotification::ReasoningSummaryPartAdded(
+                codex_app_server_protocol::ReasoningSummaryPartAddedNotification {
+                    thread_id: "thread-1".to_string(),
+                    turn_id: "turn-1".to_string(),
+                    item_id: "reasoning-1".to_string(),
+                    summary_index,
+                },
+            ),
+            /*replay_kind*/ None,
+        );
+        chat.handle_server_notification(
+            ServerNotification::ReasoningSummaryTextDelta(ReasoningSummaryTextDeltaNotification {
+                thread_id: "thread-1".to_string(),
+                turn_id: "turn-1".to_string(),
+                item_id: "reasoning-1".to_string(),
+                delta: delta.to_string(),
+                summary_index,
+            }),
+            /*replay_kind*/ None,
+        );
+    }
+
+    chat.handle_server_notification(
+        ServerNotification::ItemCompleted(ItemCompletedNotification {
+            thread_id: "thread-1".to_string(),
+            turn_id: "turn-1".to_string(),
+            completed_at_ms: 0,
+            item: AppServerThreadItem::Reasoning {
+                id: "reasoning-1".to_string(),
+                summary: vec![
+                    "**Plan**\n\ndone".to_string(),
+                    "**Checking tests**\n\n<!-- -->".to_string(),
+                ],
+                content: Vec::new(),
+            },
+        }),
+        /*replay_kind*/ None,
+    );
+
+    let rendered = match rx.try_recv() {
+        Ok(AppEvent::InsertHistoryCell(cell)) => {
+            lines_to_single_string(&cell.transcript_lines(/*width*/ 80))
+        }
+        other => panic!("expected InsertHistoryCell, got {other:?}"),
+    };
+    assert_eq!(rendered, "• done\n");
+}
+
 #[tokio::test]
 async fn thread_snapshot_replayed_turn_started_marks_task_running() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;

codex-rs/tui/src/chatwidget/turn_runtime.rs

@@ -80,7 +80,7 @@ impl ChatWidget {
         if self.mcp_startup_status.is_none() || !self.status_header_is_mcp_startup_owned() {
             self.set_status_header(String::from("Working"));
         }
-        self.full_reasoning_buffer.clear();
+        self.reasoning_summary_parts.clear();
         self.reasoning_buffer.clear();
         self.set_ambient_pet_notification(
             crate::pets::PetNotificationKind::Running,

codex-rs/tui/src/history_cell/messages.rs

@@ -495,37 +495,70 @@ pub(crate) fn new_user_prompt(
 /// Create the reasoning history cell emitted at the end of a reasoning block.
 ///
 /// The helper snapshots `cwd` into the returned cell so local file links render the same way they
-/// did while the turn was live, even if rendering happens after other app state has advanced.
+/// did while the turn was live, even if rendering happens after other app state has advanced. Part
+/// boundaries are preserved so standalone empty placeholders can be removed without changing
+/// literal HTML comments or bold-only summary content.
 pub(crate) fn new_reasoning_summary_block(
-    full_reasoning_buffer: String,
+    reasoning_parts: Vec<String>,
     cwd: &Path,
 ) -> Box<dyn HistoryCell> {
-    let cwd = cwd.to_path_buf();
-    let full_reasoning_buffer = full_reasoning_buffer.trim();
-    if let Some(open) = full_reasoning_buffer.find("**") {
-        let after_open = &full_reasoning_buffer[(open + 2)..];
-        if let Some(close) = after_open.find("**") {
-            let after_close_idx = open + 2 + close + 2;
-            // if we don't have anything beyond `after_close_idx`
-            // then we don't have a summary to inject into history
-            if after_close_idx < full_reasoning_buffer.len() {
-                let header_buffer = full_reasoning_buffer[..after_close_idx].to_string();
-                let summary_buffer = full_reasoning_buffer[after_close_idx..].to_string();
-                // Preserve the session cwd so local file links render the same way in the
-                // collapsed reasoning block as they did while streaming live content.
-                return Box::new(ReasoningSummaryCell::new(
-                    header_buffer,
-                    summary_buffer,
-                    &cwd,
-                    /*transcript_only*/ false,
-                ));
-            }
-        }
-    }
+    let (header, content) = split_reasoning_summary_parts(&reasoning_parts);
+    let transcript_only = header.is_empty();
     Box::new(ReasoningSummaryCell::new(
-        "".to_string(),
-        full_reasoning_buffer.to_string(),
-        &cwd,
-        /*transcript_only*/ true,
+        header,
+        content,
+        cwd,
+        transcript_only,
     ))
 }
+
+/// Split structured reasoning-summary parts into the status header and renderable content.
+pub(crate) fn split_reasoning_summary_parts(reasoning_parts: &[String]) -> (String, String) {
+    let mut leading_empty_part_header = None;
+    let mut content_parts = Vec::with_capacity(reasoning_parts.len());
+
+    for part in reasoning_parts {
+        let part = part.trim();
+        if part.is_empty() {
+            continue;
+        }
+
+        let header_end = part.strip_prefix("**").and_then(|after_open| {
+            after_open
+                .find("**")
+                .and_then(|close| (close > 0).then_some(close + 4))
+        });
+        let body = header_end.map_or(part, |header_end| &part[header_end..]);
+        if body.trim() == "<!-- -->" {
+            if content_parts.is_empty()
+                && leading_empty_part_header.is_none()
+                && let Some(header_end) = header_end
+            {
+                leading_empty_part_header = Some(part[..header_end].to_string());
+            }
+            continue;
+        }
+
+        content_parts.push(part);
+    }
+
+    let content = content_parts.join("\n\n");
+    if content.is_empty() {
+        return (leading_empty_part_header.unwrap_or_default(), content);
+    }
+
+    if let Some(after_open) = content.strip_prefix("**")
+        && let Some(close) = after_open.find("**")
+    {
+        let after_close_idx = 2 + close + 2;
+        let after_close = &content[after_close_idx..];
+        if after_close.starts_with('\n') || after_close.starts_with('\r') {
+            return (
+                content[..after_close_idx].to_string(),
+                after_close.to_string(),
+            );
+        }
+    }
+
+    (leading_empty_part_header.unwrap_or_default(), content)
+}

codex-rs/tui/src/history_cell/tests.rs

@@ -2249,7 +2249,7 @@ fn plan_update_does_not_split_url_like_tokens_in_note_or_step() {
 #[test]
 fn reasoning_summary_block() {
     let cell = new_reasoning_summary_block(
-        "**High level reasoning**\n\nDetailed reasoning goes here.".to_string(),
+        vec!["**High level reasoning**\n\nDetailed reasoning goes here.".to_string()],
         &test_cwd(),
     );
 
@@ -2307,8 +2307,10 @@ fn reasoning_summary_height_matches_wrapped_rendering_for_url_like_content() {
 
 #[test]
 fn reasoning_summary_block_returns_reasoning_cell_when_feature_disabled() {
-    let cell =
-        new_reasoning_summary_block("Detailed reasoning goes here.".to_string(), &test_cwd());
+    let cell = new_reasoning_summary_block(
+        vec!["Detailed reasoning goes here.".to_string()],
+        &test_cwd(),
+    );
 
     let rendered = render_transcript(cell.as_ref());
     assert_eq!(rendered, vec!["• Detailed reasoning goes here."]);
@@ -2320,7 +2322,7 @@ async fn reasoning_summary_block_respects_config_overrides() {
     config.model = Some("gpt-3.5-turbo".to_string());
     config.model_supports_reasoning_summaries = Some(true);
     let cell = new_reasoning_summary_block(
-        "**High level reasoning**\n\nDetailed reasoning goes here.".to_string(),
+        vec!["**High level reasoning**\n\nDetailed reasoning goes here.".to_string()],
         &test_cwd(),
     );
 
@@ -2331,7 +2333,7 @@ async fn reasoning_summary_block_respects_config_overrides() {
 #[test]
 fn reasoning_summary_block_falls_back_when_header_is_missing() {
     let cell = new_reasoning_summary_block(
-        "**High level reasoning without closing".to_string(),
+        vec!["**High level reasoning without closing".to_string()],
         &test_cwd(),
     );
 
@@ -2342,7 +2344,7 @@ fn reasoning_summary_block_falls_back_when_header_is_missing() {
 #[test]
 fn reasoning_summary_block_falls_back_when_summary_is_missing() {
     let cell = new_reasoning_summary_block(
-        "**High level reasoning without closing**".to_string(),
+        vec!["**High level reasoning without closing**".to_string()],
         &test_cwd(),
     );
 
@@ -2350,7 +2352,7 @@ fn reasoning_summary_block_falls_back_when_summary_is_missing() {
     assert_eq!(rendered, vec!["• High level reasoning without closing"]);
 
     let cell = new_reasoning_summary_block(
-        "**High level reasoning without closing**\n\n  ".to_string(),
+        vec!["**High level reasoning without closing**\n\n  ".to_string()],
         &test_cwd(),
     );
 
@@ -2361,7 +2363,7 @@ fn reasoning_summary_block_falls_back_when_summary_is_missing() {
 #[test]
 fn reasoning_summary_block_splits_header_and_summary_when_present() {
     let cell = new_reasoning_summary_block(
-        "**High level plan**\n\nWe should fix the bug next.".to_string(),
+        vec!["**High level plan**\n\nWe should fix the bug next.".to_string()],
         &test_cwd(),
     );
 
@@ -2372,6 +2374,100 @@ fn reasoning_summary_block_splits_header_and_summary_when_present() {
     assert_eq!(rendered_transcript, vec!["• We should fix the bug next."]);
 }
 
+#[test]
+fn reasoning_summary_block_hides_empty_html_comment_parts() {
+    let cell = new_reasoning_summary_block(
+        vec![
+            "**Checking the first thing**\n\n<!-- -->".to_string(),
+            "**Checking the second thing**\n\n<!-- -->".to_string(),
+        ],
+        &test_cwd(),
+    );
+
+    let rendered_display = render_lines(&cell.display_lines(/*width*/ 80));
+    insta::assert_snapshot!(rendered_display.join("\n"), @"");
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, Vec::<String>::new());
+}
+
+#[test]
+fn reasoning_summary_block_preserves_bold_content_after_empty_html_comment_part() {
+    let cell = new_reasoning_summary_block(
+        vec![
+            "**Status**\n\n<!-- -->".to_string(),
+            "**Important conclusion**".to_string(),
+            "<!-- -->".to_string(),
+        ],
+        &test_cwd(),
+    );
+
+    let rendered_display = render_lines(&cell.display_lines(/*width*/ 80));
+    insta::assert_snapshot!(rendered_display.join("\n"), @"• Important conclusion");
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, vec!["• Important conclusion"]);
+
+    let cell = new_reasoning_summary_block(
+        vec![
+            "**Status**\n\n<!-- -->".to_string(),
+            "**Result:** keep **this**".to_string(),
+        ],
+        &test_cwd(),
+    );
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, vec!["• Result: keep this"]);
+}
+
+#[test]
+fn reasoning_summary_block_strips_header_after_leading_empty_part() {
+    let cell = new_reasoning_summary_block(
+        vec![
+            "**Status**\n\n<!-- -->".to_string(),
+            "**Checking tests**\n\nTests passed".to_string(),
+        ],
+        &test_cwd(),
+    );
+
+    let rendered_display = render_lines(&cell.display_lines(/*width*/ 80));
+    insta::assert_snapshot!(rendered_display.join("\n"), @"• Tests passed");
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, vec!["• Tests passed"]);
+}
+
+#[test]
+fn reasoning_summary_block_drops_empty_part_after_real_content() {
+    let cell = new_reasoning_summary_block(
+        vec![
+            "**Plan**\n\ndone".to_string(),
+            "**Checking tests**\n\n<!-- -->".to_string(),
+        ],
+        &test_cwd(),
+    );
+
+    let rendered_display = render_lines(&cell.display_lines(/*width*/ 80));
+    insta::assert_snapshot!(rendered_display.join("\n"), @"• done");
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, vec!["• done"]);
+}
+
+#[test]
+fn reasoning_summary_block_preserves_literal_html_comment() {
+    let cell = new_reasoning_summary_block(
+        vec!["**Plan**\n\nUse `<!-- -->` in JSX.".to_string()],
+        &test_cwd(),
+    );
+
+    let rendered_display = render_lines(&cell.display_lines(/*width*/ 80));
+    insta::assert_snapshot!(rendered_display.join("\n"), @"• Use <!-- --> in JSX.");
+
+    let rendered_transcript = render_transcript(cell.as_ref());
+    assert_eq!(rendered_transcript, vec!["• Use <!-- --> in JSX."]);
+}
+
 #[test]
 fn deprecation_notice_renders_summary_with_details() {
     let cell = new_deprecation_notice(

codex-rs/tui/src/thread_transcript.rs

@@ -9,6 +9,7 @@ use crate::history_cell::HistoryCell;
 use crate::history_cell::PlainHistoryCell;
 use crate::history_cell::ReasoningSummaryCell;
 use crate::history_cell::UserHistoryCell;
+use crate::history_cell::split_reasoning_summary_parts;
 use crate::multi_agents::sub_agent_activity_summary;
 use codex_app_server_protocol::Thread;
 use codex_app_server_protocol::ThreadItem;
@@ -89,19 +90,17 @@ pub(crate) fn thread_to_transcript_cells(
             ThreadItem::Reasoning {
                 summary, content, ..
             } => {
-                let text = if matches!(raw_reasoning_visibility, RawReasoningVisibility::Visible)
-                    && !content.is_empty()
-                {
-                    content.join("\n\n")
-                } else {
-                    summary.join("\n\n")
-                };
+                let (header, text) =
+                    if matches!(raw_reasoning_visibility, RawReasoningVisibility::Visible)
+                        && !content.is_empty()
+                    {
+                        ("Reasoning".to_string(), content.join("\n\n"))
+                    } else {
+                        split_reasoning_summary_parts(summary)
+                    };
                 if !text.trim().is_empty() {
                     cells.push(Arc::new(ReasoningSummaryCell::new(
-                        "Reasoning".to_string(),
-                        text,
-                        cwd,
-                        /*transcript_only*/ false,
+                        header, text, cwd, /*transcript_only*/ false,
                     )));
                 }
             }