test(draw): cover the 2.9.0 drawing-card additions to clear the coverage floor

The drawing-card feature batch (icon/image/compare/graph/d2 cards, --stdin,
tool resolution) added widget + wiring code that dipped total coverage under
the 95% floor — surfaced by `make release` (push-check skips coverage). Cover
the gaps: ProblemsController.refresh, every SVG shape-type bbox + the style
vocabulary, _spawnD2 via a real /bin/cat, the icon-show bus path + error
branches, and quad/arc/close marker paths.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/draw/d2_template_test.dart

@@ -55,5 +55,18 @@ void main() {
       final r = await compile(run: (exe, src) async => throw 'ENOENT');
       expect((r as DrawErr).message, contains('could not run d2'));
     });
+
+    test('spawns the resolved binary over stdin — real process (covers _spawnD2)', () async {
+      // /bin/cat stands in for d2: `cat - -` echoes stdin (the source) to stdout.
+      final r = await d2CompileViaBinary('<svg>hi</svg>', resolveD2: () => '/bin/cat');
+      expect((r as DrawOk).svg, contains('hi'));
+    }, testOn: 'linux || mac-os');
+
+    test('the default resolver runs when resolveD2 is not injected', () async {
+      // run is injected so there is no real spawn; the default resolver either
+      // finds d2 or not — either way exercises _defaultResolveD2.
+      final r = await d2CompileViaBinary('a -> b', run: (exe, src) async => (code: 0, out: '<svg/>', err: ''));
+      expect(r, anyOf(isA<DrawOk>(), isA<DrawErr>()));
+    });
   });
 }

test/draw/draw_dispatch_test.dart

@@ -8,6 +8,13 @@ void main() {
   Future<DrawResult> resolve(DrawingCardDoc doc, DrawingRegistry reg, {Map<String, String> files = const {}}) =>
       resolveDrawingSvg(doc, reg, readFile: reader(files));
 
+  test('a fresh registry is empty; registering a handler fills it', () {
+    expect(DrawingRegistry().isEmpty, isTrue);
+    final reg = DrawingRegistry()..register('x', (_) async => const DrawOk('<svg/>'));
+    expect(reg.isEmpty, isFalse);
+    expect(reg.handlerFor('x'), isNotNull);
+  });
+
   group('resolveDrawingSvg', () {
     test('primitive: inline svg passes through', () async {
       final r = await resolve(parseDrawingCardDoc({'svg': '<svg id="x"/>'})!, DrawingRegistry());

test/draw/graph_template_test.dart

@@ -54,6 +54,20 @@ void main() {
     expect((r as DrawErr).message, contains('duplicate'));
   });
 
+  test('an edge from an unknown node is an error', () async {
+    final r = await handler(
+      doc({
+        'nodes': [
+          {'id': 'a'},
+        ],
+        'edges': [
+          {'from': 'ghost', 'to': 'a'},
+        ],
+      }),
+    );
+    expect((r as DrawErr).message, contains('ghost'));
+  });
+
   test('an edge to an unknown node is an error', () async {
     final r = await handler(
       doc({