♻️ Consolidate string truncation utilities and simplify reducer modules

Extract duplicated truncation functions into centralized utils module with
truncate_chars (character-based) and truncate_width (unicode display width)
functions. Components now import from utils instead of maintaining their own
implementations.

Simplify reducer architecture by inlining agent event handling into the main
reducer and reducing modal/navigation submodules to helper functions only.
This eliminates an unnecessary abstraction layer while keeping the code
organized.

- Add src/studio/utils.rs with comprehensive tests
- Remove duplicate truncation functions from 5 components
- Delete reducer/agent.rs, consolidate into mod.rs
- Reduce modal.rs and navigation.rs to helper functions only

Author: hyperb1iss

src/studio/components/diff_view.rs

@@ -2,6 +2,8 @@
 //!
 //! Displays git diffs with syntax highlighting for added/removed lines.
 
+use crate::studio::theme;
+use crate::studio::utils::truncate_width;
 use ratatui::Frame;
 use ratatui::layout::Rect;
 use ratatui::style::{Modifier, Style};
@@ -10,9 +12,6 @@ use ratatui::widgets::{
     Block, Borders, Paragraph, Scrollbar, ScrollbarOrientation, ScrollbarState,
 };
 use std::path::PathBuf;
-use unicode_width::UnicodeWidthStr;
-
-use crate::studio::theme;
 
 // ═══════════════════════════════════════════════════════════════════════════════
 // Diff Types
@@ -534,36 +533,6 @@ pub fn parse_diff(diff_text: &str) -> Vec<FileDiff> {
 // Rendering
 // ═══════════════════════════════════════════════════════════════════════════════
 
-/// Truncate a line to fit within the given display width (accounting for unicode)
-fn truncate_line(content: &str, max_width: usize) -> String {
-    if max_width == 0 {
-        return String::new();
-    }
-
-    let content_width = content.width();
-    if content_width <= max_width {
-        content.to_string()
-    } else if max_width <= 1 {
-        ".".to_string()
-    } else {
-        // Build string char by char until we hit width limit
-        let mut result = String::new();
-        let mut current_width = 0;
-        let target_width = max_width - 1; // Leave room for ellipsis
-
-        for c in content.chars() {
-            let char_width = c.to_string().width();
-            if current_width + char_width > target_width {
-                break;
-            }
-            result.push(c);
-            current_width += char_width;
-        }
-        result.push('…');
-        result
-    }
-}
-
 /// Render the diff view widget
 pub fn render_diff_view(
     frame: &mut Frame,
@@ -629,14 +598,14 @@ fn render_diff_line(line: &DiffLine, line_num_width: usize, width: usize) -> Lin
     match line.line_type {
         DiffLineType::FileHeader => {
             let content = format!("━━━ {} ", line.content);
-            let truncated = truncate_line(&content, width);
+            let truncated = truncate_width(&content, width);
             Line::from(vec![Span::styled(truncated, style)])
         }
         DiffLineType::HunkHeader => {
             // "     " prefix takes line_num_width * 2 + 3
             let prefix_width = line_num_width * 2 + 4;
             let max_content = width.saturating_sub(prefix_width);
-            let truncated = truncate_line(&line.content, max_content);
+            let truncated = truncate_width(&line.content, max_content);
             Line::from(vec![
                 Span::styled(
                     format!("{:>width$} ", "", width = line_num_width * 2 + 3),
@@ -671,7 +640,7 @@ fn render_diff_line(line: &DiffLine, line_num_width: usize, width: usize) -> Lin
             // Format: "XXXX │ XXXX +content"
             let fixed_width = line_num_width * 2 + 6; // " │ " (3) + " " (1) + prefix (1) + padding (1)
             let max_content = width.saturating_sub(fixed_width);
-            let truncated = truncate_line(&line.content, max_content);
+            let truncated = truncate_width(&line.content, max_content);
 
             Line::from(vec![
                 Span::styled(old_num, theme::dimmed()),

src/studio/components/file_tree.rs

@@ -14,6 +14,7 @@ use std::path::{Path, PathBuf};
 use unicode_width::UnicodeWidthStr;
 
 use crate::studio::theme;
+use crate::studio::utils::truncate_width;
 
 // ═══════════════════════════════════════════════════════════════════════════════
 // Git Status
@@ -661,7 +662,7 @@ fn render_entry(entry: &FlatEntry, is_selected: bool, width: usize) -> Line<'sta
     let max_name_width = width.saturating_sub(fixed_width);
 
     // Truncate name if needed (using unicode width)
-    let display_name = truncate_to_width(&entry.name, max_name_width);
+    let display_name = truncate_width(&entry.name, max_name_width);
 
     Line::from(vec![
         Span::styled(marker, marker_style),
@@ -681,39 +682,6 @@ fn render_entry(entry: &FlatEntry, is_selected: bool, width: usize) -> Line<'sta
     ])
 }
 
-/// Truncate a string to fit within the given display width
-fn truncate_to_width(s: &str, max_width: usize) -> String {
-    if max_width == 0 {
-        return String::new();
-    }
-
-    let s_width = s.width();
-    if s_width <= max_width {
-        return s.to_string();
-    }
-
-    if max_width <= 1 {
-        return ".".to_string();
-    }
-
-    // Find the longest prefix that fits
-    let mut result = String::new();
-    let mut current_width = 0;
-    let target_width = max_width - 1; // Reserve 1 for ellipsis
-
-    for c in s.chars() {
-        let char_width = c.to_string().width();
-        if current_width + char_width > target_width {
-            break;
-        }
-        result.push(c);
-        current_width += char_width;
-    }
-
-    result.push('…');
-    result
-}
-
 /// Get icon for file based on extension (Unicode symbols, no emoji)
 fn get_file_icon(name: &str) -> &'static str {
     // Check for special filenames first

src/studio/components/message_editor.rs

@@ -2,17 +2,16 @@
 //!
 //! Text editor for commit messages using tui-textarea.
 
+use crate::studio::theme;
+use crate::studio::utils::truncate_width;
+use crate::types::GeneratedMessage;
 use crossterm::event::{KeyCode, KeyEvent};
 use ratatui::Frame;
 use ratatui::layout::Rect;
 use ratatui::style::{Modifier, Style};
 use ratatui::text::{Line, Span};
 use ratatui::widgets::{Block, Borders, Paragraph};
 use tui_textarea::TextArea;
-use unicode_width::UnicodeWidthStr;
-
-use crate::studio::theme;
-use crate::types::GeneratedMessage;
 
 // ═══════════════════════════════════════════════════════════════════════════════
 // Message Editor State
@@ -300,35 +299,6 @@ pub fn render_message_editor(
     }
 }
 
-/// Truncate a string to fit within the given display width (accounting for unicode)
-fn truncate_str(s: &str, max_width: usize) -> String {
-    if max_width == 0 {
-        return String::new();
-    }
-    let s_width = s.width();
-    if s_width <= max_width {
-        s.to_string()
-    } else if max_width <= 1 {
-        ".".to_string()
-    } else {
-        // Build string char by char until we hit width limit
-        let mut result = String::new();
-        let mut current_width = 0;
-        let target_width = max_width - 1; // Leave room for ellipsis
-
-        for c in s.chars() {
-            let char_width = c.to_string().width();
-            if current_width + char_width > target_width {
-                break;
-            }
-            result.push(c);
-            current_width += char_width;
-        }
-        result.push('…');
-        result
-    }
-}
-
 /// Render the message in view mode (non-editing)
 fn render_message_view(frame: &mut Frame, area: Rect, state: &MessageEditorState) {
     let Some(msg) = state.current_generated() else {
@@ -345,7 +315,7 @@ fn render_message_view(frame: &mut Frame, area: Rect, state: &MessageEditorState
     } else {
         width.saturating_sub(emoji.chars().count() + 1)
     };
-    let title = truncate_str(&msg.title, title_width);
+    let title = truncate_width(&msg.title, title_width);
 
     if emoji.is_empty() {
         lines.push(Line::from(Span::styled(
@@ -372,7 +342,7 @@ fn render_message_view(frame: &mut Frame, area: Rect, state: &MessageEditorState
 
     // Body (truncated lines)
     for body_line in msg.message.lines() {
-        let truncated = truncate_str(body_line, width);
+        let truncated = truncate_width(body_line, width);
         lines.push(Line::from(Span::styled(
             truncated,
             Style::default().fg(theme::TEXT_PRIMARY),
@@ -402,7 +372,7 @@ pub fn render_message_preview(msg: &GeneratedMessage, width: usize) -> Line<'sta
     } else {
         width.saturating_sub(emoji.chars().count() + 1)
     };
-    let title = truncate_str(&msg.title, title_width);
+    let title = truncate_width(&msg.title, title_width);
 
     if emoji.is_empty() {
         Line::from(Span::styled(title, theme::dimmed()))

src/studio/history.rs

@@ -29,16 +29,8 @@ const MAX_CHAT_MESSAGES: usize = 500;
 /// Max content versions per (mode, `content_type`) key
 const MAX_CONTENT_VERSIONS: usize = 50;
 
-/// UTF-8 safe string truncation (no panic on multi-byte boundaries)
-fn truncate_preview(s: &str, max_chars: usize) -> String {
-    if s.chars().count() <= max_chars {
-        s.to_string()
-    } else {
-        format!("{}...", s.chars().take(max_chars).collect::<String>())
-    }
-}
-
 use super::state::Mode;
+use super::utils::truncate_chars;
 
 // ═══════════════════════════════════════════════════════════════════════════════
 // Session Metadata (for persistence)
@@ -281,7 +273,7 @@ impl History {
             },
             change: HistoryChange::ChatMessage {
                 role,
-                preview: truncate_preview(content, 100),
+                preview: truncate_chars(content, 100),
             },
         };
 
@@ -321,7 +313,7 @@ impl History {
             },
             change: HistoryChange::ChatMessage {
                 role,
-                preview: truncate_preview(content, 100),
+                preview: truncate_chars(content, 100),
             },
         };
 

src/studio/mod.rs

@@ -24,6 +24,7 @@ mod reducer;
 mod render;
 mod state;
 mod theme;
+pub mod utils;
 
 // Submodules
 pub mod components;