test sweep: cover escape parser + render _onScroll listener (T-91)

Six tests for the last reachable coverage gaps in the terminal tree:

- EscapeParser CSI handlers that read params[0] and normalise 0 → 1:
  CUF (ESC [ Ps C), CUB (ESC [ Ps D), CPL (ESC [ Ps F).
- insertLines with an explicit param (ESC [ Ps L).
- DEC private mode 1001 (HighlightMouseTracking) toggles MouseMode
  .upDownScroll on, none off.
- RenderTerminal._onScroll driven via a test ViewportOffset that
  exposes notifyListeners — verifies the listener body runs without
  throwing when an offset is swapped in via the setter.

Coverage: escape/parser.dart 503/513 -> 510/513 (the 3 remaining
lines are _CSI.toString — only reachable from a debug log call that
no production path makes); render.dart 245/249 -> 249/249.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/terminal/parser_and_scroll_test.dart

@@ -0,0 +1,124 @@
+/// Coverage closeouts for `lib/src/terminal/src/core/escape/parser.dart`
+/// (CUF/CUB/CPL with explicit param, insertLines with param, DEC mouse
+/// mode 1001) and `lib/src/terminal/src/ui/render.dart` (the _onScroll
+/// listener body, driven via a test ViewportOffset that exposes
+/// notifyListeners).
+library;
+
+import 'package:clide/src/terminal/src/core/mouse/mode.dart';
+import 'package:clide/src/terminal/src/terminal.dart';
+import 'package:clide/src/terminal/src/terminal_view.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+/// Minimal ViewportOffset that exposes `notifyListeners` so we can fire
+/// it from a test. The real ScrollPositionWithSingleContext is hidden
+/// inside Scrollable; this stand-in lets us drive the offset setter
+/// path on RenderTerminal directly.
+class _TestViewportOffset extends ViewportOffset {
+  @override
+  double get pixels => 0;
+  @override
+  bool get hasPixels => true;
+  @override
+  bool applyViewportDimension(double viewportDimension) => true;
+  @override
+  bool applyContentDimensions(double minScrollExtent, double maxScrollExtent) => true;
+  @override
+  void correctBy(double correction) {}
+  @override
+  void jumpTo(double pixels) {}
+  @override
+  Future<void> animateTo(double to, {required Duration duration, required Curve curve}) async {}
+  @override
+  ScrollDirection get userScrollDirection => ScrollDirection.idle;
+  @override
+  bool get allowImplicitScrolling => false;
+
+  void fire() => notifyListeners();
+}
+
+Widget _host(Widget child) => Directionality(
+      textDirection: TextDirection.ltr,
+      child: MediaQuery(
+        data: const MediaQueryData(),
+        child: Center(child: SizedBox(width: 400, height: 200, child: child)),
+      ),
+    );
+
+void main() {
+  group('EscapeParser — explicit-param CSI cursor moves', () {
+    test('CUF (ESC [ Ps C) reads params[0] and normalises 0 → 1', () {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      t.write('A');
+      // Cursor at (1,0). Move forward 3 cells, write 'B'.
+      t.write('\x1b[3C');
+      t.write('B');
+      expect(t.buffer.cursorX, greaterThanOrEqualTo(4));
+      // Param of 0 normalises to 1.
+      t.write('\x1b[0C');
+      t.write('C');
+      expect(t.buffer.cursorX, greaterThanOrEqualTo(5));
+    });
+
+    test('CUB (ESC [ Ps D) reads params[0] and normalises 0 → 1', () {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      t.write('ABCDEFG');
+      // Now at column 7. Step back 3.
+      t.write('\x1b[3D');
+      // Then 0-normalised step back 1.
+      t.write('\x1b[0D');
+      expect(t.buffer.cursorX, lessThan(7));
+    });
+
+    test('CPL (ESC [ Ps F) reads params[0] and normalises 0 → 1', () {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      t.write('line1\r\nline2\r\nline3');
+      // Cursor on row 2. Go up 2 lines.
+      t.write('\x1b[2F');
+      // Then 0-normalised up 1.
+      t.write('\x1b[0F');
+      // Just verify the cursor moved upward — exact row is implementation
+      // detail, but it shouldn't still be at row 2.
+      expect(t.buffer.cursorY, lessThan(2));
+    });
+
+    test('insertLines (ESC [ Ps L) reads params[0]', () {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      t.write('row0\r\nrow1\r\nrow2');
+      // Move cursor to home and insert 2 blank lines — just verifies the
+      // path runs without throwing.
+      t.write('\x1b[H\x1b[2L');
+    });
+
+    test('DEC private mode 1001 routes to MouseMode.upDownScroll', () {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      // Enable mode 1001.
+      t.write('\x1b[?1001h');
+      expect(t.mouseMode, MouseMode.upDownScroll);
+      // Disable returns to none.
+      t.write('\x1b[?1001l');
+      expect(t.mouseMode, MouseMode.none);
+    });
+  });
+
+  group('RenderTerminal — _onScroll listener', () {
+    testWidgets('viewport-offset notifyListeners fires _onScroll without throwing', (tester) async {
+      final t = Terminal(maxLines: 100, onOutput: (_) {});
+      await tester.pumpWidget(_host(TerminalView(t)));
+      await tester.pump();
+      final r = tester.state<TerminalViewState>(find.byType(TerminalView)).renderTerminal;
+      // Swap in a viewport offset we can fire on. The offset setter
+      // attaches _onScroll as a listener.
+      final off = _TestViewportOffset();
+      r.offset = off;
+      // Force a layout so attach() has wired up listeners.
+      await tester.pump();
+      // Drive the listener — runs the body of _onScroll (markNeedsLayout
+      // + _notifyEditableRect).
+      off.fire();
+      await tester.pump();
+    });
+  });
+}