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/kernel/src/panels/drag_resize_test.dart

@@ -19,28 +19,28 @@ void main() {
 
     testWidgets('horizontal drag adjusts the sidebar slot size', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
-          LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
-        ],
-      ));
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 40,
-            height: 200,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.sidebar,
-              axis: Axis.horizontal,
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [
+            LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
+            LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
+          ],
+        ),
+      );
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 40,
+              height: 200,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.sidebar, axis: Axis.horizontal),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       final center = tester.getCenter(find.byType(DragResizeHandle));
       final gesture = await tester.startGesture(center, kind: PointerDeviceKind.mouse);
@@ -53,28 +53,28 @@ void main() {
 
     testWidgets('contextPanel drag inverts the delta sign', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
-          LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
-        ],
-      ));
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 40,
-            height: 200,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.contextPanel,
-              axis: Axis.horizontal,
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [
+            LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
+            LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
+          ],
+        ),
+      );
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 40,
+              height: 200,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.contextPanel, axis: Axis.horizontal),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       final center = tester.getCenter(find.byType(DragResizeHandle));
       final gesture = await tester.startGesture(center, kind: PointerDeviceKind.mouse);
@@ -86,28 +86,26 @@ void main() {
 
     testWidgets('exposes a slider Semantics node with the current size', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 240),
-        ],
-      ));
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 240)],
+        ),
+      );
       final semHandle = tester.ensureSemantics();
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 40,
-            height: 200,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.sidebar,
-              axis: Axis.horizontal,
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 40,
+              height: 200,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.sidebar, axis: Axis.horizontal),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       final data = tester.getSemantics(find.byType(DragResizeHandle));
       expect(data.label, 'Sidebar width');
@@ -120,28 +118,26 @@ void main() {
 
     testWidgets('contextPanel slider Semantics label matches the slot', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 320),
-        ],
-      ));
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 320)],
+        ),
+      );
       final semHandle = tester.ensureSemantics();
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 40,
-            height: 200,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.contextPanel,
-              axis: Axis.horizontal,
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 40,
+              height: 200,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.contextPanel, axis: Axis.horizontal),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       final data = tester.getSemantics(find.byType(DragResizeHandle));
       expect(data.label, 'Context panel width');
@@ -162,28 +158,26 @@ void main() {
 
     testWidgets('vertical-axis handle uses arrow up/down shortcuts and "height" label', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.workspace, position: SlotPosition.center, defaultSize: 300),
-        ],
-      ));
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [LayoutSlot(slot: Slots.workspace, position: SlotPosition.center, defaultSize: 300)],
+        ),
+      );
       final semHandle = tester.ensureSemantics();
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 200,
-            height: 40,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.workspace,
-              axis: Axis.vertical,
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 200,
+              height: 40,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.workspace, axis: Axis.vertical),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       final data = tester.getSemantics(find.byType(DragResizeHandle));
       // Custom (non-sidebar, non-contextPanel) slots fall through to
@@ -194,28 +188,28 @@ void main() {
 
     testWidgets('hovered state flips the line colour without throwing', (tester) async {
       final arr = LayoutArrangement();
-      arr.applyPreset(const LayoutPresetContribution(
-        id: 'test-preset',
-        displayName: 'Test',
-        slots: [
-          LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
-          LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
-        ],
-      ));
-      await tester.pumpWidget(harness(
-        f,
-        Center(
-          child: SizedBox(
-            width: 40,
-            height: 200,
-            child: DragResizeHandle(
-              arrangement: arr,
-              slot: Slots.sidebar,
-              axis: Axis.horizontal,
+      arr.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test-preset',
+          displayName: 'Test',
+          slots: [
+            LayoutSlot(slot: Slots.sidebar, position: SlotPosition.left, defaultSize: 200),
+            LayoutSlot(slot: Slots.contextPanel, position: SlotPosition.right, defaultSize: 200),
+          ],
+        ),
+      );
+      await tester.pumpWidget(
+        harness(
+          f,
+          Center(
+            child: SizedBox(
+              width: 40,
+              height: 200,
+              child: DragResizeHandle(arrangement: arr, slot: Slots.sidebar, axis: Axis.horizontal),
             ),
           ),
         ),
-      ));
+      );
       await tester.pumpAndSettle();
       // Hover over the handle.
       final gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);

test/kernel/src/panels/registry_test.dart

@@ -3,18 +3,8 @@ import 'package:clide/kernel/kernel.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-TabContribution _tab({
-  required String id,
-  required SlotId slot,
-  int priority = 0,
-}) =>
-    TabContribution(
-      id: id,
-      slot: slot,
-      title: id,
-      priority: priority,
-      build: (_) => const SizedBox.shrink(),
-    );
+TabContribution _tab({required String id, required SlotId slot, int priority = 0}) =>
+    TabContribution(id: id, slot: slot, title: id, priority: priority, build: (_) => const SizedBox.shrink());
 
 void main() {
   group('PanelRegistry', () {
@@ -23,10 +13,7 @@ void main() {
     setUp(() => r = PanelRegistry());
 
     test('registerSlot creates an empty mount list', () {
-      r.registerSlot(const SlotDefinition(
-        id: Slots.sidebar,
-        position: SlotPosition.left,
-      ));
+      r.registerSlot(const SlotDefinition(id: Slots.sidebar, position: SlotPosition.left));
       expect(r.definitionFor(Slots.sidebar)!.position, SlotPosition.left);
       expect(r.contributionsFor(Slots.sidebar), isEmpty);
     });
@@ -65,11 +52,7 @@ void main() {
     });
 
     test('contributing a non-slot contribution is a no-op for slots', () {
-      r.contribute(CommandContribution(
-        id: 'c',
-        command: 'c',
-        run: (_) async => throw UnimplementedError(),
-      ));
+      r.contribute(CommandContribution(id: 'c', command: 'c', run: (_) async => throw UnimplementedError()));
       expect(r.tabsFor(Slots.sidebar), isEmpty);
     });
 

test/kernel/src/panels/view_pane_snapshot_test.dart

@@ -7,12 +7,7 @@ import 'package:clide/kernel/kernel.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-TabContribution _tab(String id, SlotId slot) => TabContribution(
-      id: id,
-      slot: slot,
-      title: id.toUpperCase(),
-      build: (_) => const SizedBox.shrink(),
-    );
+TabContribution _tab(String id, SlotId slot) => TabContribution(id: id, slot: slot, title: id.toUpperCase(), build: (_) => const SizedBox.shrink());
 
 void main() {
   group('snapshotViewPanes', () {
@@ -42,11 +37,13 @@ void main() {
     });
 
     test('active follows the kernel activeTab; visible follows the arrangement', () {
-      arrangement.applyPreset(const LayoutPresetContribution(
-        id: 'test',
-        displayName: 'Test',
-        slots: [LayoutSlot(slot: Slots.workspace, position: SlotPosition.center, visible: true)],
-      ));
+      arrangement.applyPreset(
+        const LayoutPresetContribution(
+          id: 'test',
+          displayName: 'Test',
+          slots: [LayoutSlot(slot: Slots.workspace, position: SlotPosition.center, visible: true)],
+        ),
+      );
       panels.contribute(_tab('claude', Slots.workspace));
       panels.contribute(_tab('editor', Slots.workspace));
       panels.activateTab(Slots.workspace, 'editor');