test(editor): controller tests for graph<->text round-trip

Four behaviour tests guarding the controller's contract with
the rest of the editor:

 - openFlow seeds the graph + clears the dirty flag against
   the freshly-captured baseline.
 - graph edits re-emit YAML into the shared CodeController
   so the text tab stays in lockstep.
 - graph edits mark the buffer dirty against the baseline;
   markSaved snaps it back to clean.
 - selectStep is idempotent: re-selecting the same step
   doesn't notify listeners (cheap rebuild guard for the
   properties panel).

11/11 tests pass.

Signed-off-by: flemming-it <sf@flemming.it>

test/editor_controller_test.dart

@@ -0,0 +1,93 @@
+// Behaviour tests for FlowEditorController — the bridge
+// between the YAML buffer + the graph + the layout sidecar.
+// The model tests cover parsing correctness; these cover
+// that the controller wires text -> graph reparsing,
+// graph -> YAML emission, selection bookkeeping, and
+// dirty/saved transitions correctly.
+
+import 'package:fai_studio_flow_editor/src/editor_controller.dart';
+import 'package:fai_studio_flow_editor/src/model/flow_graph.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('FlowEditorController', () {
+    test('openFlow seeds the graph + clears the dirty flag', () {
+      final c = FlowEditorController();
+      addTearDown(c.dispose);
+      c.openFlow('hello', '''
+name: hello
+inputs:
+  name: text
+steps:
+  - id: greet
+    use: debug.echo@^0
+    with:
+      message: \$inputs.name
+outputs:
+  greeting: \$greet.echoed
+''');
+      expect(c.activeName, 'hello');
+      expect(c.graph.steps, hasLength(1));
+      expect(c.graph.steps.single.id, 'greet');
+      expect(c.isDirty, isFalse);
+    });
+
+    test('graph edit re-emits YAML into the text buffer', () {
+      final c = FlowEditorController();
+      addTearDown(c.dispose);
+      c.openFlow('demo', '''
+name: demo
+steps:
+  - id: a
+    use: debug.echo@^0
+outputs: {}
+''');
+      final initialText = c.codeController.fullText;
+      c.applyGraphEdit(c.graph.withStepAdded(
+        const FlowStep(id: 'b', use: 'debug.echo@^0'),
+      ));
+      expect(c.codeController.fullText, isNot(initialText));
+      expect(c.codeController.fullText, contains('id: b'));
+      expect(c.graph.steps, hasLength(2));
+    });
+
+    test('graph edit marks the buffer dirty against the baseline', () {
+      final c = FlowEditorController();
+      addTearDown(c.dispose);
+      c.openFlow('demo', '''
+steps:
+  - id: a
+    use: debug.echo@^0
+outputs: {}
+''');
+      expect(c.isDirty, isFalse);
+      c.applyGraphEdit(c.graph.withStepAdded(
+        const FlowStep(id: 'b', use: 'debug.echo@^0'),
+      ));
+      expect(c.isDirty, isTrue);
+      c.markSaved();
+      expect(c.isDirty, isFalse);
+    });
+
+    test('selectStep notifies listeners only on change', () {
+      final c = FlowEditorController();
+      addTearDown(c.dispose);
+      c.openFlow('demo', '''
+steps:
+  - id: only
+    use: debug.echo@^0
+outputs: {}
+''');
+      var calls = 0;
+      c.addListener(() => calls++);
+      c.selectStep('only');
+      final after = calls;
+      // Selecting the same thing again must NOT bump the
+      // listener count — the controller short-circuits.
+      c.selectStep('only');
+      expect(calls, after);
+      c.selectStep(null);
+      expect(calls, after + 1);
+    });
+  });
+}