Add editor handlers.rs tests (15 tests, was 0)

editor/handlers.rs now has comprehensive key dispatch tests:
- Mode checks (default is Insert)
- Esc/F10 behavior (save-before-close prompt on dirty buffer)
- F2 save, F9 menubar toggle, Ctrl-Q literal insert toggle
- Backspace, Enter, Tab, printable char insertion
- Bookmark toggle, Ctrl-S syntax toggle
- Ctrl-H backspace alias (MC parity)
- Prompt mode Esc cancel
- Insert literal mode pass-through

Also: made viewer mod tests pub(crate) for cross-module test access.
1455 tests passing, zero warnings.

local/recipes/tui/tlc/source/src/editor/handlers.rs

@@ -1343,3 +1343,145 @@ fn word_at_cursor(buf: &crate::editor::buffer::Buffer, pos: usize) -> String {
     }
     text[start..end].to_string()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::editor::EditorResult;
+
+    fn empty_editor() -> Editor {
+        Editor::new_empty()
+    }
+
+    #[test]
+    fn default_mode_is_insert() {
+        let e = empty_editor();
+        assert!(matches!(e.mode(), Mode::Insert));
+    }
+
+    #[test]
+    fn esc_with_modified_prompts_save() {
+        let mut e = empty_editor();
+        e.insert_str("test");
+        e.modified = true;
+        let result = e.handle_key(Key::ESCAPE);
+        assert!(matches!(result, EditorResult::Running));
+        // Esc with dirty buffer opens save-before-close prompt
+        assert!(matches!(e.mode(), Mode::Prompt(PromptKind::SaveBeforeClose)));
+    }
+
+    #[test]
+    fn f10_with_modified_prompts_save() {
+        let mut e = empty_editor();
+        e.insert_str("test");
+        e.modified = true;
+        let result = e.handle_key(Key::f(10));
+        assert!(matches!(result, EditorResult::Running));
+        assert!(matches!(e.mode(), Mode::Prompt(PromptKind::SaveBeforeClose)));
+    }
+
+    #[test]
+    fn ctrl_s_in_insert_returns_running() {
+        let mut e = empty_editor();
+        e.insert_str("test");
+        let result = e.handle_key(Key::ctrl('s'));
+        assert!(matches!(result, EditorResult::Running));
+    }
+
+    #[test]
+    fn ctrl_q_toggles_literal_insert() {
+        let mut e = empty_editor();
+        assert!(!e.insert_literal);
+        let _ = e.handle_key(Key::ctrl('q'));
+        assert!(e.insert_literal);
+        let _ = e.handle_key(Key::ctrl('q'));
+        assert!(!e.insert_literal);
+    }
+
+    #[test]
+    fn f2_returns_save() {
+        let mut e = empty_editor();
+        let result = e.handle_key(Key::f(2));
+        assert!(matches!(result, EditorResult::Save));
+    }
+
+    #[test]
+    fn enter_in_insert_splits_line() {
+        let mut e = empty_editor();
+        e.insert_str("hello");
+        let len_before = e.buffer.len();
+        let _ = e.handle_key(Key::ENTER);
+        // Enter inserts a newline, buffer grows
+        assert!(e.buffer.len() > len_before);
+    }
+
+    #[test]
+    fn backspace_in_insert_deletes() {
+        let mut e = empty_editor();
+        e.insert_str("hello");
+        e.cursor.set_position(5, &e.buffer);
+        let len_before = e.buffer.len();
+        let _ = e.handle_key(Key::BACKSPACE);
+        assert!(e.buffer.len() < len_before);
+    }
+
+    #[test]
+    fn tab_in_insert_inserts_tab() {
+        let mut e = empty_editor();
+        let len_before = e.buffer.len();
+        let _ = e.handle_key(Key::TAB);
+        assert!(e.buffer.len() > len_before);
+    }
+
+    #[test]
+    fn printable_char_in_insert_inserts() {
+        let mut e = empty_editor();
+        let len_before = e.buffer.len();
+        let _ = e.handle_key(Key { code: b'x' as u32, mods: Modifiers::empty() });
+        assert_eq!(e.buffer.len(), len_before + 1);
+    }
+
+    #[test]
+    fn insert_literal_mode_passes_char_through() {
+        let mut e = empty_editor();
+        e.insert_literal = true;
+        // ESC in literal mode inserts the escape char, doesn't close
+        let _ = e.handle_key(Key::ESCAPE);
+        assert!(!e.insert_literal); // literal mode consumed
+    }
+
+    #[test]
+    fn f9_toggles_menubar() {
+        let mut e = empty_editor();
+        assert!(e.menubar.is_none());
+        let _ = e.handle_key(Key::f(9));
+        assert!(e.menubar.is_some());
+    }
+
+    #[test]
+    fn prompt_mode_esc_cancels() {
+        let mut e = empty_editor();
+        e.mode = Mode::Prompt(PromptKind::Find);
+        let result = e.handle_key(Key::ESCAPE);
+        assert!(matches!(result, EditorResult::Running));
+        assert!(!matches!(e.mode(), Mode::Prompt(_)));
+    }
+
+    #[test]
+    fn bookmark_toggle_switches_to_prompt() {
+        let mut e = empty_editor();
+        let _ = e.handle_key(Key::alt('m'));
+        assert!(matches!(e.mode(), Mode::Prompt(PromptKind::BookmarkSet)));
+    }
+
+    #[test]
+    fn ctrl_h_in_insert_is_backspace() {
+        let mut e = empty_editor();
+        e.insert_str("hello");
+        e.cursor.set_position(5, &e.buffer);
+        let len_before = e.buffer.len();
+        let _ = e.handle_key(Key::ctrl('h'));
+        // Ctrl-H is backspace alias (MC parity) — deletes character
+        assert_eq!(e.buffer.len(), len_before - 1);
+    }
+}