feat(tui): cache rendered message lines and throttle streaming redraws to improve TUI responsiveness

- Introduce `MessageRenderContext` and `MessageCacheEntry` for caching wrapped lines per message.
- Implement `render_message_lines_cached` using cache, invalidating on updates.
- Add role/style helpers and content hashing for cache validation.
- Throttle UI redraws in the main loop during active streaming (50 ms interval) and adjust idle tick timing.
- Update drawing logic to use cached rendering and manage draw intervals.
- Remove unused `role_color` function and adjust imports accordingly.

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Secure credential vault integration for Ollama Cloud API keys when `privacy.encrypt_local_data = true`.
 - Input panel respects a new `ui.input_max_rows` setting so long prompts expand predictably before scrolling kicks in.
 - Command palette offers fuzzy `:model` filtering and `:provider` completions for fast switching.
+- Message rendering caches wrapped lines and throttles streaming redraws to keep the TUI responsive on long sessions.
 - Chat history honors `ui.scrollback_lines`, trimming older rows to keep the TUI responsive and surfacing a "↓ New messages" badge whenever updates land off-screen.
 
 ### Changed

crates/owlen-cli/src/main.rs

@@ -478,11 +478,25 @@ async fn run_app(
     mut event_rx: mpsc::UnboundedReceiver<Event>,
     session_rx: &mut mpsc::UnboundedReceiver<SessionEvent>,
 ) -> Result<()> {
+    let stream_draw_interval = tokio::time::Duration::from_millis(50);
+    let idle_tick = tokio::time::Duration::from_millis(100);
+    let mut last_draw = tokio::time::Instant::now() - stream_draw_interval;
+
     loop {
         // Advance loading animation frame
         app.advance_loading_animation();
 
+        let streaming_active = app.streaming_count() > 0;
+        let draw_due = if streaming_active {
+            last_draw.elapsed() >= stream_draw_interval
+        } else {
+            true
+        };
+
+        if draw_due {
             terminal.draw(|f| ui::render_chat(f, app))?;
+            last_draw = tokio::time::Instant::now();
+        }
 
         // Process any pending LLM requests AFTER UI has been drawn
         if let Err(e) = app.process_pending_llm_request().await {
@@ -494,6 +508,14 @@ async fn run_app(
             eprintln!("Error processing tool execution: {}", e);
         }
 
+        let sleep_duration = if streaming_active {
+            stream_draw_interval
+                .checked_sub(last_draw.elapsed())
+                .unwrap_or_else(|| tokio::time::Duration::from_millis(0))
+        } else {
+            idle_tick
+        };
+
         tokio::select! {
             Some(event) = event_rx.recv() => {
                 if let AppState::Quit = app.handle_event(event).await? {
@@ -503,10 +525,7 @@ async fn run_app(
             Some(session_event) = session_rx.recv() => {
                 app.handle_session_event(session_event)?;
             }
-            // Add a timeout to keep the animation going even when there are no events
-            _ = tokio::time::sleep(tokio::time::Duration::from_millis(100)) => {
-                // This will cause the loop to continue and advance the animation
-            }
+            _ = tokio::time::sleep(sleep_duration) => {}
         }
     }
 }

crates/owlen-tui/src/chat_app.rs

@@ -10,6 +10,7 @@ use owlen_core::{
     ui::{AppState, AutoScroll, FocusedPanel, InputMode},
 };
 use ratatui::style::{Color, Modifier, Style};
+use ratatui::text::{Line, Span};
 use textwrap::wrap;
 use tokio::{sync::mpsc, task::JoinHandle};
 use tui_textarea::{Input, TextArea};
@@ -23,7 +24,10 @@ use crate::state::{CommandPalette, ModelPaletteEntry};
 use crate::ui::format_tool_output;
 // Agent executor moved to separate binary `owlen-agent`. The TUI no longer directly
 // imports `AgentExecutor` to avoid a circular dependency on `owlen-cli`.
+use std::borrow::Cow;
+use std::collections::hash_map::DefaultHasher;
 use std::collections::{BTreeSet, HashMap, HashSet};
+use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
 const ONBOARDING_STATUS_LINE: &str =
@@ -151,6 +155,7 @@ pub struct ChatApp {
     model_info_viewport_height: usize,            // Cached viewport height for the info panel
     expanded_provider: Option<String>,            // Which provider group is currently expanded
     current_provider: String,                     // Provider backing the active session
+    message_line_cache: HashMap<Uuid, MessageCacheEntry>, // Cached rendered lines per message
     auto_scroll: AutoScroll,                      // Auto-scroll state for message rendering
     thinking_scroll: AutoScroll,                  // Auto-scroll state for thinking panel
     viewport_height: usize,                       // Track the height of the messages viewport
@@ -208,6 +213,47 @@ pub struct ConsentDialogState {
     pub callback_id: Uuid, // ID to match callback with the request
 }
 
+#[derive(Clone)]
+struct MessageCacheEntry {
+    theme_name: String,
+    wrap_width: usize,
+    show_role_labels: bool,
+    content_hash: u64,
+    lines: Vec<Line<'static>>,
+}
+
+pub(crate) struct MessageRenderContext<'a> {
+    formatter: &'a mut owlen_core::formatting::MessageFormatter,
+    show_role_labels: bool,
+    content_width: usize,
+    is_last_message: bool,
+    is_streaming: bool,
+    loading_indicator: &'a str,
+    theme: &'a Theme,
+}
+
+impl<'a> MessageRenderContext<'a> {
+    pub(crate) fn new(
+        formatter: &'a mut owlen_core::formatting::MessageFormatter,
+        show_role_labels: bool,
+        content_width: usize,
+        is_last_message: bool,
+        is_streaming: bool,
+        loading_indicator: &'a str,
+        theme: &'a Theme,
+    ) -> Self {
+        Self {
+            formatter,
+            show_role_labels,
+            content_width,
+            is_last_message,
+            is_streaming,
+            loading_indicator,
+            theme,
+        }
+    }
+}
+
 impl ChatApp {
     pub async fn new(
         controller: SessionController,
@@ -248,6 +294,7 @@ impl ChatApp {
             model_info_viewport_height: 0,
             expanded_provider: None,
             current_provider,
+            message_line_cache: HashMap::new(),
             auto_scroll: AutoScroll::default(),
             thinking_scroll: AutoScroll::default(),
             viewport_height: 10, // Default viewport height, will be updated during rendering
@@ -759,6 +806,163 @@ impl ChatApp {
         }
     }
 
+    fn role_style(theme: &Theme, role: &Role) -> Style {
+        match role {
+            Role::User => Style::default().fg(theme.user_message_role),
+            Role::Assistant => Style::default().fg(theme.assistant_message_role),
+            Role::System => Style::default().fg(theme.unfocused_panel_border),
+            Role::Tool => Style::default().fg(theme.info),
+        }
+    }
+
+    fn content_style(theme: &Theme, role: &Role) -> Style {
+        if matches!(role, Role::Tool) {
+            Style::default().fg(theme.tool_output)
+        } else {
+            Style::default()
+        }
+    }
+
+    fn message_content_hash(role: &Role, content: &str) -> u64 {
+        let mut hasher = DefaultHasher::new();
+        role.to_string().hash(&mut hasher);
+        content.hash(&mut hasher);
+        hasher.finish()
+    }
+
+    fn invalidate_message_cache(&mut self, id: &Uuid) {
+        self.message_line_cache.remove(id);
+    }
+
+    pub(crate) fn render_message_lines_cached(
+        &mut self,
+        message_index: usize,
+        ctx: MessageRenderContext<'_>,
+    ) -> Vec<Line<'static>> {
+        let MessageRenderContext {
+            formatter,
+            show_role_labels,
+            content_width,
+            is_last_message,
+            is_streaming,
+            loading_indicator,
+            theme,
+        } = ctx;
+        let (message_id, role, raw_content) = {
+            let conversation = self.conversation();
+            let message = &conversation.messages[message_index];
+            (message.id, message.role.clone(), message.content.clone())
+        };
+
+        let display_content = if matches!(role, Role::Assistant) {
+            formatter.extract_thinking(&raw_content).0
+        } else if matches!(role, Role::Tool) {
+            format_tool_output(&raw_content)
+        } else {
+            raw_content
+        };
+
+        let formatted_lines: Vec<String> = display_content
+            .trim()
+            .lines()
+            .map(|s| s.to_string())
+            .collect();
+        let content = formatted_lines.join("\n");
+        let content_hash = Self::message_content_hash(&role, &content);
+
+        if !is_streaming
+            && let Some(entry) = self.message_line_cache.get(&message_id)
+            && entry.wrap_width == content_width
+            && entry.show_role_labels == show_role_labels
+            && entry.theme_name == theme.name
+            && entry.content_hash == content_hash
+        {
+            return entry.lines.clone();
+        }
+
+        let mut rendered: Vec<Line<'static>> = Vec::new();
+        let content_style = Self::content_style(theme, &role);
+
+        if show_role_labels {
+            let (emoji, name) = match role {
+                Role::User => ("👤 ", "You: "),
+                Role::Assistant => ("🤖 ", "Assistant: "),
+                Role::System => ("⚙️ ", "System: "),
+                Role::Tool => ("🔧 ", "Tool: "),
+            };
+
+            let mut role_line_spans = vec![
+                Span::raw(emoji),
+                Span::styled(
+                    name.to_string(),
+                    Self::role_style(theme, &role).add_modifier(Modifier::BOLD),
+                ),
+            ];
+
+            if matches!(role, Role::Assistant)
+                && is_streaming
+                && is_last_message
+                && !loading_indicator.is_empty()
+            {
+                role_line_spans.push(Span::styled(
+                    format!(" {}", loading_indicator),
+                    Style::default().fg(theme.info),
+                ));
+            }
+
+            rendered.push(Line::from(role_line_spans));
+
+            let indent = "  ";
+            let available_width = content_width.saturating_sub(2);
+            let chunks: Vec<Cow<'_, str>> = if available_width > 0 {
+                wrap(content.as_str(), available_width)
+            } else {
+                Vec::new()
+            };
+
+            let last_index = chunks.len().saturating_sub(1);
+            for (chunk_idx, seg) in chunks.into_iter().enumerate() {
+                let mut spans = vec![Span::styled(
+                    format!("{indent}{}", seg.into_owned()),
+                    content_style,
+                )];
+                if chunk_idx == last_index && is_streaming {
+                    spans.push(Span::styled(" ▌", Style::default().fg(theme.cursor)));
+                }
+                rendered.push(Line::from(spans));
+            }
+        } else {
+            let chunks: Vec<Cow<'_, str>> = if content_width > 0 {
+                wrap(content.as_str(), content_width)
+            } else {
+                Vec::new()
+            };
+            let last_index = chunks.len().saturating_sub(1);
+            for (chunk_idx, seg) in chunks.into_iter().enumerate() {
+                let mut spans = vec![Span::styled(seg.into_owned(), content_style)];
+                if chunk_idx == last_index && is_streaming {
+                    spans.push(Span::styled(" ▌", Style::default().fg(theme.cursor)));
+                }
+                rendered.push(Line::from(spans));
+            }
+        }
+
+        if !is_streaming {
+            self.message_line_cache.insert(
+                message_id,
+                MessageCacheEntry {
+                    theme_name: theme.name.clone(),
+                    wrap_width: content_width,
+                    show_role_labels,
+                    content_hash,
+                    lines: rendered.clone(),
+                },
+            );
+        }
+
+        rendered
+    }
+
     pub fn apply_chat_scrollback_trim(&mut self, removed: usize, remaining: usize) {
         if removed == 0 {
             self.chat_line_offset = 0;
@@ -807,11 +1011,13 @@ impl ChatApp {
 
     pub fn set_theme(&mut self, theme: Theme) {
         self.theme = theme;
+        self.message_line_cache.clear();
     }
 
     pub fn switch_theme(&mut self, theme_name: &str) -> Result<()> {
         if let Some(theme) = owlen_core::theme::get_theme(theme_name) {
             self.theme = theme;
+            self.message_line_cache.clear();
             // Save theme to config
             self.controller.config_mut().ui.theme = theme_name.to_string();
             if let Err(err) = config::save_config(&self.controller.config()) {
@@ -2700,6 +2906,8 @@ impl ChatApp {
                                         );
                                         self.error = None;
                                         self.update_thinking_from_last_message();
+                                        self.message_line_cache.clear();
+                                        self.chat_line_offset = 0;
                                     }
                                     Err(e) => {
                                         self.error = Some(format!("Failed to load session: {}", e));
@@ -2958,6 +3166,7 @@ impl ChatApp {
                 response,
             } => {
                 self.controller.apply_stream_chunk(message_id, &response)?;
+                self.invalidate_message_cache(&message_id);
 
                 // Update thinking content in real-time during streaming
                 self.update_thinking_from_last_message();
@@ -2991,9 +3200,11 @@ impl ChatApp {
                 if let Some(id) = message_id {
                     self.streaming.remove(&id);
                     self.stream_tasks.remove(&id);
+                    self.invalidate_message_cache(&id);
                 } else {
                     self.streaming.clear();
                     self.stream_tasks.clear();
+                    self.message_line_cache.clear();
                 }
                 self.error = Some(message);
             }
@@ -3744,6 +3955,7 @@ impl ChatApp {
                     cancel_error = Some(err.to_string());
                 }
                 self.streaming.remove(&message_id);
+                self.invalidate_message_cache(&message_id);
                 cancelled = true;
             }
         }
@@ -3801,6 +4013,7 @@ impl ChatApp {
         self.agent_mode = false;
         self.agent_running = false;
         self.is_loading = false;
+        self.message_line_cache.clear();
 
         // Ensure no orphaned stream tasks remain
         for (_, handle) in self.stream_tasks.drain() {

crates/owlen-tui/src/ui.rs

@@ -9,7 +9,7 @@ use tui_textarea::TextArea;
 use unicode_segmentation::UnicodeSegmentation;
 use unicode_width::UnicodeWidthStr;
 
-use crate::chat_app::{ChatApp, HELP_TAB_COUNT, ModelSelectorItemKind};
+use crate::chat_app::{ChatApp, HELP_TAB_COUNT, MessageRenderContext, ModelSelectorItemKind};
 use owlen_core::model::DetailedModelInfo;
 use owlen_core::types::{ModelInfo, Role};
 use owlen_core::ui::{FocusedPanel, InputMode};
@@ -677,127 +677,54 @@ fn render_messages(frame: &mut Frame<'_>, area: Rect, app: &mut ChatApp) {
     let content_width = area.width.saturating_sub(4).max(20);
     app.set_viewport_dimensions(viewport_height, usize::from(content_width));
 
-    let conversation = app.conversation();
+    let total_messages = app.message_count();
     let mut formatter = app.formatter().clone();
 
     // Reserve space for borders and the message indent so text fits within the block
     formatter.set_wrap_width(usize::from(content_width));
 
-    // Build the lines for messages
-    let mut lines: Vec<Line> = Vec::new();
-    for (message_index, message) in conversation.messages.iter().enumerate() {
-        let role = &message.role;
-        let (emoji, name) = match role {
-            Role::User => ("👤 ", "You: "),
-            Role::Assistant => ("🤖 ", "Assistant: "),
-            Role::System => ("⚙️ ", "System: "),
-            Role::Tool => ("🔧 ", "Tool: "),
-        };
-
-        // Extract content without thinking tags for assistant messages
-        let content_to_display = if matches!(role, Role::Assistant) {
-            let (content_without_think, _) = formatter.extract_thinking(&message.content);
-            content_without_think
-        } else if matches!(role, Role::Tool) {
-            // Format tool results nicely
-            format_tool_output(&message.content)
-        } else {
-            message.content.clone()
-        };
-
-        let formatted: Vec<String> = content_to_display
-            .trim()
-            .lines()
-            .map(|s| s.to_string())
-            .collect();
-        let is_streaming = message
+    // Build the lines for messages using cached rendering
+    let mut lines: Vec<Line<'static>> = Vec::new();
+    let show_role_labels = formatter.show_role_labels();
+    for message_index in 0..total_messages {
+        let is_streaming = {
+            let conversation = app.conversation();
+            conversation.messages[message_index]
                 .metadata
                 .get("streaming")
                 .and_then(|v| v.as_bool())
-            .unwrap_or(false);
-
-        let show_role_labels = formatter.show_role_labels();
-
-        if show_role_labels {
-            // Role name line
-            let mut role_line_spans = vec![
-                Span::raw(emoji),
-                Span::styled(name, role_color(role, &theme).add_modifier(Modifier::BOLD)),
-            ];
-
-            // Add loading indicator if applicable
-            if matches!(role, Role::Assistant)
-                && app.get_loading_indicator() != ""
-                && message_index == conversation.messages.len() - 1
-                && is_streaming
-            {
-                role_line_spans.push(Span::styled(
-                    format!(" {}", app.get_loading_indicator()),
-                    Style::default().fg(theme.info),
-                ));
-            }
-
-            lines.push(Line::from(role_line_spans));
-
-            // Join all formatted lines into single content string
-            let content = formatted.join("\n");
-
-            // Wrap content with available width minus indent (2 spaces)
-            let indent = "  ";
-            let available_width = (content_width as usize).saturating_sub(2);
-            let chunks = if available_width > 0 {
-                wrap(&content, available_width)
-            } else {
-                vec![]
+                .unwrap_or(false)
         };
-
-            let chunks_len = chunks.len();
-            for (i, seg) in chunks.into_iter().enumerate() {
-                let style = if matches!(role, Role::Tool) {
-                    Style::default().fg(theme.tool_output)
-                } else {
-                    Style::default()
-                };
-
-                let mut spans = vec![Span::styled(format!("{indent}{}", seg), style)];
-                if i == chunks_len - 1 && is_streaming {
-                    spans.push(Span::styled(" ▌", Style::default().fg(theme.cursor)));
-                }
-                lines.push(Line::from(spans));
-            }
-        } else {
-            // No role labels - just show content
-            let content = formatted.join("\n");
-            let chunks = wrap(&content, content_width as usize);
-            let chunks_len = chunks.len();
-            for (i, seg) in chunks.into_iter().enumerate() {
-                let style = if matches!(role, Role::Tool) {
-                    Style::default().fg(theme.tool_output)
-                } else {
-                    Style::default()
-                };
-
-                let mut spans = vec![Span::styled(seg.into_owned(), style)];
-                if i == chunks_len - 1 && is_streaming {
-                    spans.push(Span::styled(" ▌", Style::default().fg(theme.cursor)));
-                }
-                lines.push(Line::from(spans));
-            }
-        }
-
-        // Add an empty line after each message, except the last one
-        if message_index < conversation.messages.len() - 1 {
-            lines.push(Line::from(""));
+        let message_lines = app.render_message_lines_cached(
+            message_index,
+            MessageRenderContext::new(
+                &mut formatter,
+                show_role_labels,
+                content_width as usize,
+                message_index + 1 == total_messages,
+                is_streaming,
+                app.get_loading_indicator(),
+                &theme,
+            ),
+        );
+        lines.extend(message_lines);
+        if message_index + 1 < total_messages {
+            lines.push(Line::from(String::new()));
         }
     }
 
     // Add loading indicator ONLY if we're loading and there are no messages at all,
     // or if the last message is from the user (no Assistant response started yet)
-    let last_message_is_user = conversation
+    let last_message_is_user = if total_messages == 0 {
+        true
+    } else {
+        let conversation = app.conversation();
+        conversation
             .messages
             .last()
             .map(|msg| matches!(msg.role, Role::User))
-        .unwrap_or(true);
+            .unwrap_or(true)
+    };
 
     if app.get_loading_indicator() != "" && last_message_is_user {
         let loading_spans = vec![
@@ -2704,15 +2631,6 @@ fn centered_rect(percent_x: u16, percent_y: u16, area: Rect) -> Rect {
         .split(vertical[1])[1]
 }
 
-fn role_color(role: &Role, theme: &owlen_core::theme::Theme) -> Style {
-    match role {
-        Role::User => Style::default().fg(theme.user_message_role),
-        Role::Assistant => Style::default().fg(theme.assistant_message_role),
-        Role::System => Style::default().fg(theme.unfocused_panel_border),
-        Role::Tool => Style::default().fg(theme.info),
-    }
-}
-
 /// Format tool output JSON into a nice human-readable format
 pub(crate) fn format_tool_output(content: &str) -> String {
     // Try to parse as JSON