Enhance TUI scrolling: add viewport dimension tracking, autoscroll logic, and message line calculation. Refactor related components for dynamic rendering.

crates/owlen-tui/src/ui.rs

@@ -10,7 +10,7 @@ use unicode_width::UnicodeWidthStr;
 use crate::chat_app::{ChatApp, InputMode};
 use owlen_core::types::Role;
 
-pub fn render_chat(frame: &mut Frame<'_>, app: &ChatApp) {
+pub fn render_chat(frame: &mut Frame<'_>, app: &mut ChatApp) {
     // Calculate dynamic input height based on textarea content
     let available_width = frame.area().width;
     let input_height = if matches!(app.mode(), InputMode::Editing) {
@@ -345,12 +345,16 @@ fn render_header(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
     frame.render_widget(paragraph, inner_area);
 }
 
-fn render_messages(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
+fn render_messages(frame: &mut Frame<'_>, area: Rect, app: &mut ChatApp) {
+    // Calculate viewport dimensions for autoscroll calculations
+    let viewport_height = area.height.saturating_sub(2) as usize; // subtract borders
+    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 mut formatter = app.formatter().clone();
 
     // Reserve space for borders and the message indent so text fits within the block
-    let content_width = area.width.saturating_sub(4).max(20);
     formatter.set_wrap_width(usize::from(content_width));
 
     let mut lines: Vec<Line> = Vec::new();