chore(fuzz): upgrade targets, fix false positives, and add invariant assertions (#11)

- Fix insert_delete target using .unwrap() causing false-positive crashes
  on arbitrary::Error (input exhaustion)
- Fix fuzz Cargo.toml referencing wrong package name (tui-textarea vs
  tui-textarea-2)
- Add invariant assertions (cursor bounds, lines non-empty, selection
  validity) to all targets
- Add 4 new fuzz targets: undo_redo, selection, wrap_render, search
- Expand existing targets with full delete/insert variant coverage,
  input_without_shortcuts, set_yank_text, set_max_histories, and clear
- Add DummyBackend::resize() for variable-width wrap rendering tests

fuzz/fuzz_targets/insert_delete.rs

@@ -1,26 +1,93 @@
 #![no_main]
 
-use arbitrary::{Arbitrary as _, Result, Unstructured};
+use arbitrary::{Arbitrary, Result, Unstructured};
 use libfuzzer_sys::fuzz_target;
 use tui_textarea::{CursorMove, TextArea};
 use tui_textarea_bench::{dummy_terminal, TerminalExt};
 
+#[derive(Arbitrary)]
+enum Op {
+    Move(CursorMove),
+    InsertStr(String),
+    InsertChar(char),
+    InsertTab,
+    InsertNewline,
+    DeleteStr(usize),
+    DeleteChar,
+    DeleteNextChar,
+    DeleteWord,
+    DeleteNextWord,
+    DeleteLineByEnd,
+    DeleteLineByHead,
+    DeleteNewline,
+    Clear,
+}
+
+fn assert_invariants(textarea: &TextArea<'_>) {
+    let lines = textarea.lines();
+    assert!(!lines.is_empty(), "lines must never be empty");
+    let (row, col) = textarea.cursor();
+    assert!(
+        row < lines.len(),
+        "cursor row {row} out of bounds (lines: {})",
+        lines.len()
+    );
+    assert!(
+        col <= lines[row].chars().count(),
+        "cursor col {col} out of bounds (line {row} chars: {})",
+        lines[row].chars().count(),
+    );
+}
+
 fn fuzz(data: &[u8]) -> Result<()> {
     let mut term = dummy_terminal();
     let mut textarea = TextArea::default();
     let mut data = Unstructured::new(data);
-    for i in 0..100 {
-        textarea.move_cursor(CursorMove::arbitrary(&mut data)?);
-        if i % 2 == 0 {
-            textarea.insert_str(String::arbitrary(&mut data)?);
-        } else {
-            textarea.delete_str(usize::arbitrary(&mut data)?);
+    for _ in 0..100 {
+        match Op::arbitrary(&mut data)? {
+            Op::Move(m) => textarea.move_cursor(m),
+            Op::InsertStr(s) => {
+                textarea.insert_str(s);
+            }
+            Op::InsertChar(c) => textarea.insert_char(c),
+            Op::InsertTab => {
+                textarea.insert_tab();
+            }
+            Op::InsertNewline => textarea.insert_newline(),
+            Op::DeleteStr(n) => {
+                textarea.delete_str(n);
+            }
+            Op::DeleteChar => {
+                textarea.delete_char();
+            }
+            Op::DeleteNextChar => {
+                textarea.delete_next_char();
+            }
+            Op::DeleteWord => {
+                textarea.delete_word();
+            }
+            Op::DeleteNextWord => {
+                textarea.delete_next_word();
+            }
+            Op::DeleteLineByEnd => {
+                textarea.delete_line_by_end();
+            }
+            Op::DeleteLineByHead => {
+                textarea.delete_line_by_head();
+            }
+            Op::DeleteNewline => {
+                textarea.delete_newline();
+            }
+            Op::Clear => {
+                textarea.clear();
+            }
         }
         term.draw_textarea(&textarea);
+        assert_invariants(&textarea);
     }
     Ok(())
 }
 
 fuzz_target!(|data: &[u8]| {
-    fuzz(data).unwrap();
+    let _ = fuzz(data);
 });