first ai version of formula screen

aider.sh

@@ -1,3 +1,2 @@
-aider --git --watch-files --read README.md --read CLAUDE.md
-notify-send "LLM session ended"
+aider --git --watch-files --read CLAUDE.md --notifications
 

lib/ai/unit_dropdown.dart

@@ -0,0 +1,38 @@
+import 'package:flutter/material.dart';
+import '../../formula_models.dart';
+import '../../corpus.dart';
+
+class UnitDropdown extends StatelessWidget {
+  final UnitCorpus corpus;
+  final VariableSpec variable;
+  final String? selectedUnit;
+  final ValueChanged<String?> onUnitChanged;
+
+  const UnitDropdown({
+    super.key,
+    required this.corpus,
+    required this.variable,
+    required this.selectedUnit,
+    required this.onUnitChanged,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final availableUnits = corpus.allUnits().where((unit) => unit.baseUnit == variable.magnitude).toList();
+
+    return DropdownButton<String>(
+      value: selectedUnit ?? variable.magnitude,
+      icon: const Icon(Icons.arrow_drop_down),
+      elevation: 16,
+      style: TextStyle(color: Theme.of(context).colorScheme.primary, fontSize: 14),
+      underline: Container(height: 1, color: Theme.of(context).dividerColor),
+      onChanged: onUnitChanged,
+      items: availableUnits.map<DropdownMenuItem<String>>((UnitSpec unit) {
+        return DropdownMenuItem<String>(
+          value: unit.name,
+          child: Text(unit.symbol, style: const TextStyle(fontSize: 14)),
+        );
+      }).toList(),
+    );
+  }
+}

lib/ai/unit_list.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import '../corpus.dart';
 import '../formula_models.dart';
+import 'formula_screen.dart';
 
 class UnitList extends StatefulWidget {
   final UnitCorpus corpus;
@@ -54,7 +55,7 @@ class _UnitListState extends State<UnitList> {
                   VariableSpec(name: 'velocity', magnitude: 'meters_per_second'),
                 ],
                 output: VariableSpec(name: 'energy', magnitude: 'joules'),
-                d4rtCode: "main() {\n  return 0.5 * mass * velocity * velocity;\n}",
+                d4rtCode: "energy = 0.5 * mass * velocity * velocity;",
               );
               
               Navigator.push(

lib/corpus.dart

@@ -93,4 +93,6 @@ class UnitCorpus {
 
     return xTo;
   }
+
+  Iterable<UnitSpec> allUnits() => _allUnits.values;
 }

lib/main.dart

@@ -2,9 +2,12 @@ import 'package:d4rt_formulas/ai/FormulaWidget.dart';
 import 'package:d4rt_formulas/formula_models.dart';
 import 'package:flutter/material.dart';
 
-import 'package:resource/resource.dart';
+import 'package:resource_portable/resource.dart' show Resource;
 import 'dart:convert';
 
+import 'ai/unit_list.dart';
+import 'corpus.dart';
+
 void main() {
   runApp(MaterialApp(
     home: FutureBuilder<UnitCorpus>(