feat(claudbg-pow4): add cursor movement to filter/search bar input

Add filter_cursor and search_cursor fields to AppState; handle Left/Right
to move cursor, Home/End to jump, cursor-aware Backspace (deletes before
cursor), and cursor-aware character insertion. Render the cursor at the
correct mid-text position. Update help modal to document new bindings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.beans/claudbg-pow4--tui-cursor-movement-in-filtersearch-bar-leftright.md

@@ -1,10 +1,11 @@
 ---
 # claudbg-pow4
 title: 'TUI: cursor movement in filter/search bar (left/right arrow keys)'
-status: todo
+status: in-progress
 type: feature
+priority: normal
 created_at: 2026-04-01T16:47:09Z
-updated_at: 2026-04-01T16:47:09Z
+updated_at: 2026-04-01T17:00:18Z
 ---
 
 Support moving the cursor left and right within the Filter/Search bar text input so users can edit text in the middle of the input without having to delete everything first.

src/tui/modals/help_modal.rs

@@ -16,7 +16,7 @@ use crate::tui::state::AppState;
 
 /// Dialog dimensions.
 const DIALOG_WIDTH: u16 = 36;
-const DIALOG_HEIGHT: u16 = 38;
+const DIALOG_HEIGHT: u16 = 42;
 
 /// Compute a centered [`Rect`] of the given size within `area`.
 fn centered_rect(width: u16, height: u16, area: Rect) -> Rect {
@@ -48,6 +48,8 @@ const HELP_TEXT: &str = "\
 \n\
  Filter (sessions)\n\
   t / /     open filter\n\
+  ←/→       move cursor\n\
+  Home/End  jump to start/end\n\
   Enter     apply & close\n\
   Esc       clear input\n\
 \n\
@@ -64,6 +66,8 @@ const HELP_TEXT: &str = "\
 \n\
  Search (transcript)\n\
   t / /     open search\n\
+  ←/→       move cursor\n\
+  Home/End  jump to start/end\n\
   n / N     next/prev match\n\
   Enter     apply & close\n\
   Esc       clear & close\n\

src/tui/screens/session_list.rs

@@ -175,9 +175,30 @@ fn render_filter_bar(f: &mut Frame, area: Rect, state: &AppState) {
     // Build the content line: label + input text (+ cursor when focused).
     let label = Span::styled("Filter: ", Style::default().add_modifier(Modifier::BOLD));
     let input_text = if focused {
-        // Show a block cursor at end of input.
-        let mut spans = vec![label, Span::raw(state.filter_input.clone())];
-        spans.push(Span::styled("█", Style::default().fg(Color::Yellow)));
+        // Split the input at the cursor position and insert a block cursor glyph.
+        let cursor = state.filter_cursor.min(state.filter_input.len());
+        let before = &state.filter_input[..cursor];
+        let after = &state.filter_input[cursor..];
+        // The cursor glyph replaces the character under it (or is appended when at end).
+        let (cursor_char, after_rest) = if after.is_empty() {
+            ("█", "")
+        } else {
+            let first_char_end = after
+                .char_indices()
+                .nth(1)
+                .map(|(i, _)| i)
+                .unwrap_or(after.len());
+            (&after[..first_char_end], &after[first_char_end..])
+        };
+        let spans = vec![
+            label,
+            Span::raw(before.to_string()),
+            Span::styled(
+                cursor_char,
+                Style::default().fg(Color::Black).bg(Color::Yellow),
+            ),
+            Span::raw(after_rest.to_string()),
+        ];
         Line::from(spans)
     } else if state.filter_input.is_empty() && state.filter_active.is_empty() {
         Line::from(vec![
@@ -262,11 +283,13 @@ pub fn handle_session_list_event(event: Event, state: &mut AppState) -> bool {
         // Focus the filter input directly.
         KeyCode::Char('t') | KeyCode::Char('/') => {
             state.focus = Focus::FilterInput;
+            state.filter_cursor = state.filter_input.len();
             true
         }
         // Tab cycles focus: list → filter → list.
         KeyCode::Tab => {
             state.focus = Focus::FilterInput;
+            state.filter_cursor = state.filter_input.len();
             true
         }
         // Quit — show confirmation dialog rather than exiting immediately.
@@ -288,18 +311,66 @@ pub fn handle_session_list_event(event: Event, state: &mut AppState) -> bool {
 /// Returns `true` when the event is consumed.
 fn handle_filter_input_event(code: KeyCode, state: &mut AppState) -> bool {
     match code {
-        // Character input: append to filter_input and reset history browsing.
+        // Character input: insert at cursor position and reset history browsing.
         KeyCode::Char(c) => {
-            state.filter_input.push(c);
+            let pos = state.filter_cursor;
+            state.filter_input.insert(pos, c);
+            state.filter_cursor += c.len_utf8();
             state.filter_history_pos = None;
             true
         }
-        // Backspace: remove last char.
+        // Backspace: remove the character *before* the cursor.
         KeyCode::Backspace => {
-            state.filter_input.pop();
+            if state.filter_cursor > 0 {
+                // Find the start of the previous UTF-8 character.
+                let pos = state.filter_cursor;
+                let prev = state.filter_input[..pos]
+                    .char_indices()
+                    .next_back()
+                    .map(|(i, _)| i)
+                    .unwrap_or(0);
+                state.filter_input.remove(prev);
+                state.filter_cursor = prev;
+            }
             state.filter_history_pos = None;
             true
         }
+        // Left arrow: move cursor one character to the left.
+        KeyCode::Left => {
+            if state.filter_cursor > 0 {
+                let pos = state.filter_cursor;
+                let prev = state.filter_input[..pos]
+                    .char_indices()
+                    .next_back()
+                    .map(|(i, _)| i)
+                    .unwrap_or(0);
+                state.filter_cursor = prev;
+            }
+            true
+        }
+        // Right arrow: move cursor one character to the right.
+        KeyCode::Right => {
+            let pos = state.filter_cursor;
+            if pos < state.filter_input.len() {
+                let next = state.filter_input[pos..]
+                    .char_indices()
+                    .nth(1)
+                    .map(|(i, _)| pos + i)
+                    .unwrap_or(state.filter_input.len());
+                state.filter_cursor = next;
+            }
+            true
+        }
+        // Home: jump cursor to start of input.
+        KeyCode::Home => {
+            state.filter_cursor = 0;
+            true
+        }
+        // End: jump cursor to end of input.
+        KeyCode::End => {
+            state.filter_cursor = state.filter_input.len();
+            true
+        }
         // Enter: apply the current input as the active filter and return focus to the list.
         KeyCode::Enter => {
             let query = state.filter_input.trim().to_string();
@@ -326,6 +397,7 @@ fn handle_filter_input_event(code: KeyCode, state: &mut AppState) -> bool {
         // Escape: clear the text input (but keep the panel visible).
         KeyCode::Esc => {
             state.filter_input.clear();
+            state.filter_cursor = 0;
             state.filter_history_pos = None;
             true
         }
@@ -340,6 +412,7 @@ fn handle_filter_input_event(code: KeyCode, state: &mut AppState) -> bool {
             };
             state.filter_history_pos = Some(new_pos);
             state.filter_input = state.filter_history[new_pos].clone();
+            state.filter_cursor = state.filter_input.len();
             true
         }
         // Down arrow: browse forward through history (or clear when past the end).
@@ -351,10 +424,12 @@ fn handle_filter_input_event(code: KeyCode, state: &mut AppState) -> bool {
                 let new_pos = pos + 1;
                 state.filter_history_pos = Some(new_pos);
                 state.filter_input = state.filter_history[new_pos].clone();
+                state.filter_cursor = state.filter_input.len();
             } else {
                 // Past the end: clear input and stop browsing history.
                 state.filter_history_pos = None;
                 state.filter_input.clear();
+                state.filter_cursor = 0;
             }
             true
         }
@@ -642,8 +717,10 @@ mod tests {
         let mut state = AppState::new();
         state.focus = Focus::FilterInput;
         state.filter_input = "mo".to_string();
+        state.filter_cursor = 2; // cursor at end
         handle_session_list_event(press(KeyCode::Backspace), &mut state);
         assert_eq!(state.filter_input, "m");
+        assert_eq!(state.filter_cursor, 1);
     }
 
     #[test]
@@ -729,4 +806,110 @@ mod tests {
         assert_eq!(state.filter_input, "");
         assert_eq!(state.filter_history_pos, None);
     }
+
+    // ── Filter cursor movement ───────────────────────────────────────────────
+
+    #[test]
+    fn char_inserts_at_cursor_not_end() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "ac".to_string();
+        state.filter_cursor = 1; // cursor between 'a' and 'c'
+        handle_session_list_event(press(KeyCode::Char('b')), &mut state);
+        assert_eq!(state.filter_input, "abc");
+        assert_eq!(state.filter_cursor, 2);
+    }
+
+    #[test]
+    fn backspace_deletes_before_cursor_not_end() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 2; // cursor between 'b' and 'c'
+        handle_session_list_event(press(KeyCode::Backspace), &mut state);
+        assert_eq!(state.filter_input, "ac");
+        assert_eq!(state.filter_cursor, 1);
+    }
+
+    #[test]
+    fn backspace_at_start_does_nothing() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 0;
+        handle_session_list_event(press(KeyCode::Backspace), &mut state);
+        assert_eq!(state.filter_input, "abc");
+        assert_eq!(state.filter_cursor, 0);
+    }
+
+    #[test]
+    fn left_moves_cursor_back() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 2;
+        handle_session_list_event(press(KeyCode::Left), &mut state);
+        assert_eq!(state.filter_cursor, 1);
+    }
+
+    #[test]
+    fn left_clamps_at_zero() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 0;
+        handle_session_list_event(press(KeyCode::Left), &mut state);
+        assert_eq!(state.filter_cursor, 0);
+    }
+
+    #[test]
+    fn right_moves_cursor_forward() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 1;
+        handle_session_list_event(press(KeyCode::Right), &mut state);
+        assert_eq!(state.filter_cursor, 2);
+    }
+
+    #[test]
+    fn right_clamps_at_end() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 3;
+        handle_session_list_event(press(KeyCode::Right), &mut state);
+        assert_eq!(state.filter_cursor, 3);
+    }
+
+    #[test]
+    fn home_jumps_to_start() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 3;
+        handle_session_list_event(press(KeyCode::Home), &mut state);
+        assert_eq!(state.filter_cursor, 0);
+    }
+
+    #[test]
+    fn end_jumps_to_end() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 0;
+        handle_session_list_event(press(KeyCode::End), &mut state);
+        assert_eq!(state.filter_cursor, 3);
+    }
+
+    #[test]
+    fn esc_resets_cursor_to_zero() {
+        let mut state = AppState::new();
+        state.focus = Focus::FilterInput;
+        state.filter_input = "abc".to_string();
+        state.filter_cursor = 2;
+        handle_session_list_event(press(KeyCode::Esc), &mut state);
+        assert_eq!(state.filter_input, "");
+        assert_eq!(state.filter_cursor, 0);
+    }
 }

src/tui/screens/transcript.rs

@@ -379,8 +379,29 @@ fn render_search_bar(f: &mut Frame, area: Rect, state: &AppState) {
 
     let label = Span::styled("Search: ", Style::default().add_modifier(Modifier::BOLD));
     let input_line = if focused {
-        let mut spans = vec![label, Span::raw(state.search_input.clone())];
-        spans.push(Span::styled("█", Style::default().fg(Color::Yellow)));
+        // Split the input at the cursor position and insert a block cursor glyph.
+        let cursor = state.search_cursor.min(state.search_input.len());
+        let before = &state.search_input[..cursor];
+        let after = &state.search_input[cursor..];
+        let (cursor_char, after_rest) = if after.is_empty() {
+            ("█", "")
+        } else {
+            let first_char_end = after
+                .char_indices()
+                .nth(1)
+                .map(|(i, _)| i)
+                .unwrap_or(after.len());
+            (&after[..first_char_end], &after[first_char_end..])
+        };
+        let spans = vec![
+            label,
+            Span::raw(before.to_string()),
+            Span::styled(
+                cursor_char,
+                Style::default().fg(Color::Black).bg(Color::Yellow),
+            ),
+            Span::raw(after_rest.to_string()),
+        ];
         Line::from(spans)
     } else if state.search_input.is_empty() && state.search_active.is_empty() {
         Line::from(vec![
@@ -568,6 +589,10 @@ pub fn handle_transcript_event(event: Event, state: &mut AppState) -> bool {
                 Focus::SubagentsPanel => Focus::SearchInput,
                 Focus::SearchInput | Focus::FilterInput => Focus::ChatLog,
             };
+            // When switching into the search bar, position the cursor at the end.
+            if state.focus == Focus::SearchInput {
+                state.search_cursor = state.search_input.len();
+            }
             true
         }
         // Navigate back: from SubagentTranscript → parent session transcript;
@@ -596,6 +621,7 @@ pub fn handle_transcript_event(event: Event, state: &mut AppState) -> bool {
         // Jump directly to the search input.
         KeyCode::Char('t') | KeyCode::Char('/') => {
             state.focus = Focus::SearchInput;
+            state.search_cursor = state.search_input.len();
             true
         }
         // Next match.
@@ -726,14 +752,61 @@ pub fn handle_transcript_event(event: Event, state: &mut AppState) -> bool {
 /// Returns `true` when the event is consumed.
 fn handle_search_input_event(code: KeyCode, state: &mut AppState) -> bool {
     match code {
-        // Character input: append to search_input.
+        // Character input: insert at cursor position.
         KeyCode::Char(c) => {
-            state.search_input.push(c);
+            let pos = state.search_cursor;
+            state.search_input.insert(pos, c);
+            state.search_cursor += c.len_utf8();
             true
         }
-        // Backspace: remove last char.
+        // Backspace: remove the character *before* the cursor.
         KeyCode::Backspace => {
-            state.search_input.pop();
+            if state.search_cursor > 0 {
+                let pos = state.search_cursor;
+                let prev = state.search_input[..pos]
+                    .char_indices()
+                    .next_back()
+                    .map(|(i, _)| i)
+                    .unwrap_or(0);
+                state.search_input.remove(prev);
+                state.search_cursor = prev;
+            }
+            true
+        }
+        // Left arrow: move cursor one character to the left.
+        KeyCode::Left => {
+            if state.search_cursor > 0 {
+                let pos = state.search_cursor;
+                let prev = state.search_input[..pos]
+                    .char_indices()
+                    .next_back()
+                    .map(|(i, _)| i)
+                    .unwrap_or(0);
+                state.search_cursor = prev;
+            }
+            true
+        }
+        // Right arrow: move cursor one character to the right.
+        KeyCode::Right => {
+            let pos = state.search_cursor;
+            if pos < state.search_input.len() {
+                let next = state.search_input[pos..]
+                    .char_indices()
+                    .nth(1)
+                    .map(|(i, _)| pos + i)
+                    .unwrap_or(state.search_input.len());
+                state.search_cursor = next;
+            }
+            true
+        }
+        // Home: jump cursor to start of input.
+        KeyCode::Home => {
+            state.search_cursor = 0;
+            true
+        }
+        // End: jump cursor to end of input.
+        KeyCode::End => {
+            state.search_cursor = state.search_input.len();
             true
         }
         // Enter: apply the search, compute match lines, return focus to ChatLog.
@@ -753,6 +826,7 @@ fn handle_search_input_event(code: KeyCode, state: &mut AppState) -> bool {
         // Escape: clear search and return focus to ChatLog.
         KeyCode::Esc => {
             state.search_input.clear();
+            state.search_cursor = 0;
             state.search_active.clear();
             state.search_match_lines.clear();
             state.search_current_match = 0;
@@ -1337,8 +1411,10 @@ mod tests {
         let mut state = transcript_state();
         state.focus = Focus::SearchInput;
         state.search_input = "hi".to_string();
+        state.search_cursor = 2; // cursor at end
         handle_transcript_event(press(KeyCode::Backspace), &mut state);
         assert_eq!(state.search_input, "h");
+        assert_eq!(state.search_cursor, 1);
     }
 
     #[test]
@@ -1492,4 +1568,110 @@ mod tests {
         let consumed = handle_transcript_event(Event::FocusGained, &mut state);
         assert!(!consumed);
     }
+
+    // ── Search cursor movement ────────────────────────────────────────────────
+
+    #[test]
+    fn search_char_inserts_at_cursor_not_end() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "ac".to_string();
+        state.search_cursor = 1; // between 'a' and 'c'
+        handle_transcript_event(press(KeyCode::Char('b')), &mut state);
+        assert_eq!(state.search_input, "abc");
+        assert_eq!(state.search_cursor, 2);
+    }
+
+    #[test]
+    fn search_backspace_deletes_before_cursor_not_end() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 2; // between 'b' and 'c'
+        handle_transcript_event(press(KeyCode::Backspace), &mut state);
+        assert_eq!(state.search_input, "ac");
+        assert_eq!(state.search_cursor, 1);
+    }
+
+    #[test]
+    fn search_backspace_at_start_does_nothing() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 0;
+        handle_transcript_event(press(KeyCode::Backspace), &mut state);
+        assert_eq!(state.search_input, "abc");
+        assert_eq!(state.search_cursor, 0);
+    }
+
+    #[test]
+    fn search_left_moves_cursor_back() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 2;
+        handle_transcript_event(press(KeyCode::Left), &mut state);
+        assert_eq!(state.search_cursor, 1);
+    }
+
+    #[test]
+    fn search_left_clamps_at_zero() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 0;
+        handle_transcript_event(press(KeyCode::Left), &mut state);
+        assert_eq!(state.search_cursor, 0);
+    }
+
+    #[test]
+    fn search_right_moves_cursor_forward() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 1;
+        handle_transcript_event(press(KeyCode::Right), &mut state);
+        assert_eq!(state.search_cursor, 2);
+    }
+
+    #[test]
+    fn search_right_clamps_at_end() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 3;
+        handle_transcript_event(press(KeyCode::Right), &mut state);
+        assert_eq!(state.search_cursor, 3);
+    }
+
+    #[test]
+    fn search_home_jumps_to_start() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 3;
+        handle_transcript_event(press(KeyCode::Home), &mut state);
+        assert_eq!(state.search_cursor, 0);
+    }
+
+    #[test]
+    fn search_end_jumps_to_end() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 0;
+        handle_transcript_event(press(KeyCode::End), &mut state);
+        assert_eq!(state.search_cursor, 3);
+    }
+
+    #[test]
+    fn search_esc_resets_cursor_to_zero() {
+        let mut state = transcript_state();
+        state.focus = Focus::SearchInput;
+        state.search_input = "abc".to_string();
+        state.search_cursor = 2;
+        handle_transcript_event(press(KeyCode::Esc), &mut state);
+        assert_eq!(state.search_input, "");
+        assert_eq!(state.search_cursor, 0);
+    }
 }

src/tui/state.rs

@@ -132,6 +132,11 @@ pub struct AppState {
     // ── Search ──────────────────────────────────────────────────────────────
     /// Text currently being typed in the transcript search box.
     pub search_input: String,
+    /// Cursor position (byte offset) within `search_input`.
+    ///
+    /// Always points to a valid UTF-8 char boundary.  Ranges from `0`
+    /// (before the first character) to `search_input.len()` (after the last).
+    pub search_cursor: usize,
     /// The last applied search query (highlights all case-insensitive matches).
     /// Empty string means no search is active.
     pub search_active: String,
@@ -154,6 +159,11 @@ pub struct AppState {
     // ── Filter ──────────────────────────────────────────────────────────────
     /// Text currently being typed in the filter input box.
     pub filter_input: String,
+    /// Cursor position (byte offset) within `filter_input`.
+    ///
+    /// Always points to a valid UTF-8 char boundary.  Ranges from `0`
+    /// (before the first character) to `filter_input.len()` (after the last).
+    pub filter_cursor: usize,
     /// The last successfully applied filter query string.
     /// Empty string means no filter is active.
     pub filter_active: String,
@@ -248,6 +258,7 @@ impl AppState {
             transcript_h_scroll: 0,
             transcript_page_height: 0,
             search_input: String::new(),
+            search_cursor: 0,
             search_active: String::new(),
             search_match_lines: Vec::new(),
             search_current_match: 0,
@@ -257,6 +268,7 @@ impl AppState {
             show_quit_dialog: false,
             show_help: false,
             filter_input: String::new(),
+            filter_cursor: 0,
             filter_active: String::new(),
             filter_history,
             filter_history_pos: None,
@@ -281,6 +293,7 @@ impl AppState {
         self.transcript_scroll = 0;
         self.transcript_h_scroll = 0;
         self.search_input.clear();
+        self.search_cursor = 0;
         self.search_active.clear();
         self.search_match_lines.clear();
         self.search_current_match = 0;
@@ -306,6 +319,7 @@ impl AppState {
         self.transcript_scroll = 0;
         self.transcript_h_scroll = 0;
         self.search_input.clear();
+        self.search_cursor = 0;
         self.search_active.clear();
         self.search_match_lines.clear();
         self.search_current_match = 0;
@@ -325,6 +339,7 @@ impl AppState {
         self.transcript_scroll = 0;
         self.transcript_h_scroll = 0;
         self.search_input.clear();
+        self.search_cursor = 0;
         self.search_active.clear();
         self.search_match_lines.clear();
         self.search_current_match = 0;
@@ -344,6 +359,7 @@ impl AppState {
         self.transcript_scroll = 0;
         self.transcript_h_scroll = 0;
         self.search_input.clear();
+        self.search_cursor = 0;
         self.search_active.clear();
         self.search_match_lines.clear();
         self.search_current_match = 0;