chore: adopt Dart 3.9 toolchain — honest floor + tall-style reformat (T-353)

Raise the declared minimums in pubspec.yaml to what our deps already
require: Flutter >=3.35.0 / Dart >=3.9.0 (was 3.19.0 / 3.5.0). alchemist
0.12 needs Flutter 3.32; Dart 3.9 first ships in Flutter 3.35, so 3.35 is
the binding floor. Pin the exact build toolchain in .fvmrc (Flutter
3.44.1).

Moving to the Dart 3.9 language level switches `dart format` to the new
"tall" style and enables two new lints. This commit is the resulting
mechanical churn, isolated from any behaviour change:
  - whole-tree `dart format` reformat (tall style)
  - `dart fix` for unnecessary_underscores + use_null_aware_elements

No runtime behaviour change; `make test` green.

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

test/goldens/clide_button_goldens_test.dart

@@ -32,54 +32,23 @@ void main() {
         ),
         GoldenTestScenario(
           name: 'primary / enabled',
-          child: _wrap(
-            f,
-            ClideButton(
-              label: 'Commit',
-              onPressed: () {},
-              variant: ClideButtonVariant.primary,
-            ),
-          ),
+          child: _wrap(f, ClideButton(label: 'Commit', onPressed: () {}, variant: ClideButtonVariant.primary)),
         ),
         GoldenTestScenario(
           name: 'primary / disabled',
-          child: _wrap(
-            f,
-            const ClideButton(
-              label: 'Commit',
-              onPressed: null,
-              variant: ClideButtonVariant.primary,
-            ),
-          ),
+          child: _wrap(f, const ClideButton(label: 'Commit', onPressed: null, variant: ClideButtonVariant.primary)),
         ),
         GoldenTestScenario(
           name: 'subtle / enabled',
-          child: _wrap(
-            f,
-            ClideButton(
-              label: 'Open',
-              onPressed: () {},
-              variant: ClideButtonVariant.subtle,
-            ),
-          ),
+          child: _wrap(f, ClideButton(label: 'Open', onPressed: () {}, variant: ClideButtonVariant.subtle)),
         ),
         GoldenTestScenario(
           name: 'subtle / disabled',
-          child: _wrap(
-            f,
-            const ClideButton(
-              label: 'Open',
-              onPressed: null,
-              variant: ClideButtonVariant.subtle,
-            ),
-          ),
+          child: _wrap(f, const ClideButton(label: 'Open', onPressed: null, variant: ClideButtonVariant.subtle)),
         ),
       ],
     ),
   );
 }
 
-Widget _wrap(KernelFixture f, Widget child) => SizedBox(
-      width: 140,
-      child: harness(f, child),
-    );
+Widget _wrap(KernelFixture f, Widget child) => SizedBox(width: 140, child: harness(f, child));

test/goldens/clide_icon_goldens_test.dart

@@ -29,14 +29,7 @@ void main() {
         ])
           GoldenTestScenario(
             name: pair.$1,
-            child: harness(
-              f,
-              SizedBox(
-                width: 24,
-                height: 24,
-                child: ClideIcon(pair.$2, size: 24),
-              ),
-            ),
+            child: harness(f, SizedBox(width: 24, height: 24, child: ClideIcon(pair.$2, size: 24))),
           ),
       ],
     ),

test/goldens/collapser_card_goldens_test.dart

@@ -15,23 +15,29 @@ void main() {
   // A stand-in inner item card: content + its own per-item status mark (the
   // collapser carries the aggregate; items keep their own — T-305).
   Widget item(String label, ClideRunStatus status) => Padding(
-        padding: const EdgeInsets.only(bottom: 10),
-        child: DecoratedBox(
-          decoration: BoxDecoration(
-            border: Border.all(color: const Color(0xFF393E48)),
-            borderRadius: BorderRadius.circular(3),
-          ),
-          child: Padding(
-            padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 8),
-            child: Row(
-              children: [
-                Expanded(child: Text(label, style: const TextStyle(fontSize: 11, color: Color(0xFF6A7280)), textDirection: TextDirection.ltr)),
-                ClideStatusIndicator(status: status, size: 12),
-              ],
+    padding: const EdgeInsets.only(bottom: 10),
+    child: DecoratedBox(
+      decoration: BoxDecoration(
+        border: Border.all(color: const Color(0xFF393E48)),
+        borderRadius: BorderRadius.circular(3),
+      ),
+      child: Padding(
+        padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 8),
+        child: Row(
+          children: [
+            Expanded(
+              child: Text(
+                label,
+                style: const TextStyle(fontSize: 11, color: Color(0xFF6A7280)),
+                textDirection: TextDirection.ltr,
+              ),
             ),
-          ),
+            ClideStatusIndicator(status: status, size: 12),
+          ],
         ),
-      );
+      ),
+    ),
+  );
 
   goldenTest(
     'ClideCollapserCard (T-305): collapsed color variants + expanded inner canvas',
@@ -42,37 +48,43 @@ void main() {
         GoldenTestScenario(
           name: 'collapsed — default (muted)',
           child: _wrap(
-              f,
-              const ClideCollapserCard(
-                  label: 'Activity',
-                  collapsedSummary: 'Read  conversation_view.dart',
-                  counter: '3 steps',
-                  status: ClideRunStatus.success,
-                  children: [SizedBox.shrink()])),
+            f,
+            const ClideCollapserCard(
+              label: 'Activity',
+              collapsedSummary: 'Read  conversation_view.dart',
+              counter: '3 steps',
+              status: ClideRunStatus.success,
+              children: [SizedBox.shrink()],
+            ),
+          ),
         ),
         GoldenTestScenario(
           name: 'collapsed — edits (teal color)',
           child: _wrap(
-              f,
-              const ClideCollapserCard(
-                  label: 'Edits',
-                  color: Color(0xFF00AB9A),
-                  collapsedSummary: 'clide_markdown.dart',
-                  counter: '7 edits',
-                  status: ClideRunStatus.success,
-                  children: [SizedBox.shrink()])),
+            f,
+            const ClideCollapserCard(
+              label: 'Edits',
+              color: Color(0xFF00AB9A),
+              collapsedSummary: 'clide_markdown.dart',
+              counter: '7 edits',
+              status: ClideRunStatus.success,
+              children: [SizedBox.shrink()],
+            ),
+          ),
         ),
         GoldenTestScenario(
           name: 'collapsed — error (red color)',
           child: _wrap(
-              f,
-              const ClideCollapserCard(
-                  label: 'Bash',
-                  color: Color(0xFFF06C6F),
-                  collapsedSummary: 'npm test',
-                  counter: '1 step',
-                  status: ClideRunStatus.error,
-                  children: [SizedBox.shrink()])),
+            f,
+            const ClideCollapserCard(
+              label: 'Bash',
+              color: Color(0xFFF06C6F),
+              collapsedSummary: 'npm test',
+              counter: '1 step',
+              status: ClideRunStatus.error,
+              children: [SizedBox.shrink()],
+            ),
+          ),
         ),
         GoldenTestScenario(
           name: 'expanded — inner canvas of item cards',

test/goldens/conversation_card_goldens_test.dart

@@ -64,7 +64,12 @@ void main() {
               collapsedByDefault: true,
               collapsedSummary: '/lib/main.dart',
               body: Text('/lib/main.dart', textDirection: TextDirection.ltr),
-              extraSegments: [CardSegment(label: 'result', child: Text('void main() {}', textDirection: TextDirection.ltr))],
+              extraSegments: [
+                CardSegment(
+                  label: 'result',
+                  child: Text('void main() {}', textDirection: TextDirection.ltr),
+                ),
+              ],
             ),
           ),
         ),
@@ -80,7 +85,12 @@ void main() {
               collapsible: true,
               collapsedByDefault: false,
               body: Text('/lib/main.dart', textDirection: TextDirection.ltr),
-              extraSegments: [CardSegment(label: 'result', child: Text('void main() {}', textDirection: TextDirection.ltr))],
+              extraSegments: [
+                CardSegment(
+                  label: 'result',
+                  child: Text('void main() {}', textDirection: TextDirection.ltr),
+                ),
+              ],
             ),
           ),
         ),
@@ -97,8 +107,14 @@ void main() {
               collapsedByDefault: false,
               body: Text('{ "description": "explore the codebase" }', textDirection: TextDirection.ltr),
               extraSegments: [
-                CardSegment(label: 'prompt', child: Text('find all the widgets and summarise', textDirection: TextDirection.ltr)),
-                CardSegment(label: 'result', child: Text('found 42 widgets', textDirection: TextDirection.ltr)),
+                CardSegment(
+                  label: 'prompt',
+                  child: Text('find all the widgets and summarise', textDirection: TextDirection.ltr),
+                ),
+                CardSegment(
+                  label: 'result',
+                  child: Text('found 42 widgets', textDirection: TextDirection.ltr),
+                ),
               ],
             ),
           ),
@@ -178,7 +194,4 @@ void main() {
   );
 }
 
-Widget _wrap(KernelFixture f, Widget child) => SizedBox(
-      width: 360,
-      child: harness(f, child),
-    );
+Widget _wrap(KernelFixture f, Widget child) => SizedBox(width: 360, child: harness(f, child));

test/goldens/flutter_test_config.dart

@@ -5,8 +5,5 @@ import 'package:alchemist/alchemist.dart';
 import '../helpers/golden_harness.dart';
 
 Future<void> testExecutable(FutureOr<void> Function() testMain) async {
-  return AlchemistConfig.runWithConfig(
-    config: clideGoldenConfig(),
-    run: testMain,
-  );
+  return AlchemistConfig.runWithConfig(config: clideGoldenConfig(), run: testMain);
 }

test/goldens/tool_collapser_goldens_test.dart

@@ -17,16 +17,26 @@ void main() {
   tearDown(() async => f.dispose());
 
   Widget bashContent() => const ConversationCard(
-        variant: ConversationCardVariant.bordered,
-        accent: Color(0xFF4C9AFF),
-        label: 'Bash',
-        status: ConversationCardStatus.success,
-        body: Text('npm test', style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)), textDirection: TextDirection.ltr),
-        extraSegments: [
-          CardSegment(
-              label: 'result', child: Text('All 42 tests passed', style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)), textDirection: TextDirection.ltr)),
-        ],
-      );
+    variant: ConversationCardVariant.bordered,
+    accent: Color(0xFF4C9AFF),
+    label: 'Bash',
+    status: ConversationCardStatus.success,
+    body: Text(
+      'npm test',
+      style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)),
+      textDirection: TextDirection.ltr,
+    ),
+    extraSegments: [
+      CardSegment(
+        label: 'result',
+        child: Text(
+          'All 42 tests passed',
+          style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)),
+          textDirection: TextDirection.ltr,
+        ),
+      ),
+    ],
+  );
 
   goldenTest(
     'single tool collapser (T-305): collapsed ticker + expanded inner card',