refactor(ui): one canonical segment control (ChainSegments) everywhere

The same single-select choice pattern appeared as four widgets:
audit's hover pills, the store's SegmentedButton, the store filter
dialog's ChoiceChips, and the approvals TabBar (usertest finding
#14 / night-log decision 'pill segment as canon'). The audit
pattern is promoted to a shared ChainSegments widget (optional
icons, hover, selected border, button+selected semantics) and all
four sites use it; approvals switches lists via IndexedStack so
both stay alive and switching does not refetch.

Guard per the no-bugfix-without-a-guard rule: widget tests for
selection + semantics, plus a canon sweep that bans
TabBar/TabBarView/TabController/SegmentedButton/ChoiceChip from
lib/ (comments exempt). Deliberately out of scope: the flow
editor's Graph/Text/Run tabs live in the separate editor package.
Studio 0.75.0; guide images regenerated, dark + light verified.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/about_info.dart

@@ -4,7 +4,7 @@
 
 /// Studio's own build version. Bump on every UI release so the
 /// running app self-identifies.
-const String kStudioVersion = '0.74.0';
+const String kStudioVersion = '0.75.0';
 
 const String kProductName = 'Ch∆In Studio';
 const String kVendorName = 'Flemming.AI (F∆I)';

lib/pages/approvals.dart

@@ -36,9 +36,12 @@ class ApprovalsPage extends StatefulWidget {
   State<ApprovalsPage> createState() => _ApprovalsPageState();
 }
 
-class _ApprovalsPageState extends State<ApprovalsPage>
-    with SingleTickerProviderStateMixin {
-  late final TabController _tab;
+class _ApprovalsPageState extends State<ApprovalsPage> {
+  /// 0 = pending inbox, 1 = history. Plain index instead of a
+  /// TabController: the page uses the canonical pill segment
+  /// (ChainSegments), and an IndexedStack keeps both lists alive
+  /// so switching does not refetch.
+  int _tabIndex = 0;
   late Future<List<ApprovalRecord>> _pendingFuture;
   late Future<List<ApprovalRecord>> _historyFuture;
 
@@ -63,7 +66,6 @@ class _ApprovalsPageState extends State<ApprovalsPage>
   @override
   void initState() {
     super.initState();
-    _tab = TabController(length: 2, vsync: this);
     Workspace.instance.addListener(_refresh);
     Workspace.instance.ensureLoaded();
     _refresh();
@@ -72,7 +74,6 @@ class _ApprovalsPageState extends State<ApprovalsPage>
   @override
   void dispose() {
     Workspace.instance.removeListener(_refresh);
-    _tab.dispose();
     super.dispose();
   }
 
@@ -262,12 +263,33 @@ class _ApprovalsPageState extends State<ApprovalsPage>
       backgroundColor: theme.scaffoldBackgroundColor,
       appBar: AppBar(
         title: Text(AppLocalizations.of(context)!.approvalsTitle),
-        bottom: TabBar(
-          controller: _tab,
-          tabs: [
-            Tab(text: AppLocalizations.of(context)!.approvalsTabPending),
-            Tab(text: AppLocalizations.of(context)!.approvalsTabHistory),
-          ],
+        bottom: PreferredSize(
+          preferredSize: const Size.fromHeight(44),
+          child: Align(
+            alignment: Alignment.centerLeft,
+            child: Padding(
+              padding: const EdgeInsets.fromLTRB(
+                ChainSpace.xl,
+                0,
+                ChainSpace.xl,
+                ChainSpace.sm,
+              ),
+              child: ChainSegments<int>(
+                items: [
+                  ChainSegmentItem(
+                    0,
+                    AppLocalizations.of(context)!.approvalsTabPending,
+                  ),
+                  ChainSegmentItem(
+                    1,
+                    AppLocalizations.of(context)!.approvalsTabHistory,
+                  ),
+                ],
+                value: _tabIndex,
+                onChanged: (i) => setState(() => _tabIndex = i),
+              ),
+            ),
+          ),
         ),
         actions: [
           const ChainWorkspaceSwitcher(),
@@ -285,8 +307,8 @@ class _ApprovalsPageState extends State<ApprovalsPage>
           const SizedBox(width: ChainSpace.sm),
         ],
       ),
-      body: TabBarView(
-        controller: _tab,
+      body: IndexedStack(
+        index: _tabIndex,
         children: [
           _PendingList(
             future: _pendingFuture,

lib/pages/audit.dart

@@ -634,86 +634,10 @@ class _FilterChips extends StatelessWidget {
   Widget build(BuildContext context) {
     final l = AppLocalizations.of(context)!;
     final items = _filterItems(l);
-    return Row(
-      children: [
-        for (final (v, label) in items)
-          Padding(
-            padding: const EdgeInsets.only(left: ChainSpace.xs),
-            child: _ChipButton(
-              label: label,
-              selected: value == v,
-              onTap: () => onChanged(v),
-            ),
-          ),
-      ],
-    );
-  }
-}
-
-class _ChipButton extends StatefulWidget {
-  final String label;
-  final bool selected;
-  final VoidCallback onTap;
-
-  const _ChipButton({
-    required this.label,
-    required this.selected,
-    required this.onTap,
-  });
-
-  @override
-  State<_ChipButton> createState() => _ChipButtonState();
-}
-
-class _ChipButtonState extends State<_ChipButton> {
-  bool _hovered = false;
-
-  @override
-  Widget build(BuildContext context) {
-    final theme = Theme.of(context);
-    final fg = widget.selected
-        ? theme.colorScheme.primary
-        : _hovered
-        ? theme.colorScheme.onSurface
-        : theme.colorScheme.onSurfaceVariant;
-    final bg = widget.selected
-        ? theme.colorScheme.primary.withValues(alpha: 0.12)
-        : _hovered
-        ? theme.colorScheme.surfaceContainerHigh
-        : Colors.transparent;
-    return MouseRegion(
-      onEnter: (_) => setState(() => _hovered = true),
-      onExit: (_) => setState(() => _hovered = false),
-      cursor: SystemMouseCursors.click,
-      child: GestureDetector(
-        onTap: widget.onTap,
-        child: AnimatedContainer(
-          duration: ChainMotion.fast,
-          padding: const EdgeInsets.symmetric(
-            horizontal: ChainSpace.md,
-            vertical: 6,
-          ),
-          decoration: BoxDecoration(
-            color: bg,
-            borderRadius: BorderRadius.circular(ChainRadius.sm),
-            border: Border.all(
-              color: widget.selected
-                  ? theme.colorScheme.primary.withValues(alpha: 0.3)
-                  : Colors.transparent,
-            ),
-          ),
-          child: Text(
-            widget.label,
-            // UI label, not a value — mono is reserved for
-            // paths/identifiers (usertest finding: the chips
-            // read as foreign bodies in the header).
-            style: theme.textTheme.labelMedium?.copyWith(
-              fontWeight: widget.selected ? FontWeight.w600 : FontWeight.w400,
-              color: fg,
-            ),
-          ),
-        ),
-      ),
+    return ChainSegments<String>(
+      items: [for (final (v, label) in items) ChainSegmentItem(v, label)],
+      value: value,
+      onChanged: onChanged,
     );
   }
 }

lib/pages/store.dart

@@ -365,25 +365,22 @@ class _StorePageState extends State<StorePage> {
                         Padding(
                           padding:
                               const EdgeInsets.only(bottom: ChainSpace.md),
-                          child: SegmentedButton<bool>(
-                            segments: [
-                              ButtonSegment(
-                                value: false,
-                                label: Text(l.storeSegmentModules),
-                                icon: const Icon(Icons.extension_outlined,
-                                    size: 16),
+                          child: ChainSegments<bool>(
+                            items: [
+                              ChainSegmentItem(
+                                false,
+                                l.storeSegmentModules,
+                                icon: Icons.extension_outlined,
                               ),
-                              ButtonSegment(
-                                value: true,
-                                label: Text(l.storeSegmentStudio),
-                                icon:
-                                    const Icon(Icons.palette_outlined, size: 16),
+                              ChainSegmentItem(
+                                true,
+                                l.storeSegmentStudio,
+                                icon: Icons.palette_outlined,
                               ),
                             ],
-                            selected: {_showStudio},
-                            showSelectedIcon: false,
-                            onSelectionChanged: (s) =>
-                                setState(() => _showStudio = s.first),
+                            value: _showStudio,
+                            onChanged: (v) =>
+                                setState(() => _showStudio = v),
                           ),
                         ),
                         if (_aiThinking ||
@@ -1161,17 +1158,10 @@ class _FilterDialogState extends State<_FilterDialog> {
       List<({String value, String label})> items,
       String selected,
       void Function(String) onSelect,
-    ) => Wrap(
-      spacing: ChainSpace.xs,
-      runSpacing: ChainSpace.xs,
-      children: [
-        for (final i in items)
-          _ChoiceChip(
-            label: i.label,
-            selected: selected == i.value,
-            onSelected: () => onSelect(i.value),
-          ),
-      ],
+    ) => ChainSegments<String>(
+      items: [for (final i in items) ChainSegmentItem(i.value, i.label)],
+      value: selected,
+      onChanged: onSelect,
     );
     return AlertDialog(
       title: Text(l.storeFilterLabel),
@@ -1569,31 +1559,6 @@ Up to 5 matches, ordered by best fit first. Use only module names that appear in
   }
 }
 
-class _ChoiceChip extends StatelessWidget {
-  final String label;
-  final bool selected;
-  final VoidCallback onSelected;
-
-  const _ChoiceChip({
-    required this.label,
-    required this.selected,
-    required this.onSelected,
-  });
-
-  @override
-  Widget build(BuildContext context) {
-    return Padding(
-      padding: const EdgeInsets.only(right: ChainSpace.xs),
-      child: ChoiceChip(
-        label: Text(label),
-        selected: selected,
-        onSelected: (_) => onSelected(),
-        showCheckmark: false,
-      ),
-    );
-  }
-}
-
 /// Responsive grid — wraps to as many columns as the viewport
 /// allows. Cards are click-to-expand; install is also a top-
 /// level action so single-click installs are still possible.

lib/widgets/chain_segments.dart

@@ -0,0 +1,137 @@
+// ChainSegments — THE single-select segment control (usertest
+// finding #14 / night-log decision "pill segment as canon"):
+// the same choice pattern used to appear as four different
+// widgets (audit's hover pills, store's Material SegmentedButton,
+// store-filter ChoiceChips, approvals' TabBar). One look now:
+// text pills, primary-tinted when selected, quiet hover — the
+// audit page's pattern promoted to a shared widget.
+//
+// Single-select only by design. Multi-select filters are a
+// different pattern (checkbox list), not a segment control.
+
+import 'package:flutter/material.dart';
+
+import '../theme/tokens.dart';
+
+class ChainSegmentItem<T> {
+  final T value;
+  final String label;
+  final IconData? icon;
+
+  const ChainSegmentItem(this.value, this.label, {this.icon});
+}
+
+class ChainSegments<T> extends StatelessWidget {
+  final List<ChainSegmentItem<T>> items;
+  final T value;
+  final ValueChanged<T> onChanged;
+
+  const ChainSegments({
+    super.key,
+    required this.items,
+    required this.value,
+    required this.onChanged,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Wrap(
+      spacing: ChainSpace.xs,
+      runSpacing: ChainSpace.xs,
+      children: [
+        for (final item in items)
+          _SegmentPill(
+            label: item.label,
+            icon: item.icon,
+            selected: item.value == value,
+            onTap: () {
+              if (item.value != value) onChanged(item.value);
+            },
+          ),
+      ],
+    );
+  }
+}
+
+class _SegmentPill extends StatefulWidget {
+  final String label;
+  final IconData? icon;
+  final bool selected;
+  final VoidCallback onTap;
+
+  const _SegmentPill({
+    required this.label,
+    required this.icon,
+    required this.selected,
+    required this.onTap,
+  });
+
+  @override
+  State<_SegmentPill> createState() => _SegmentPillState();
+}
+
+class _SegmentPillState extends State<_SegmentPill> {
+  bool _hovered = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final fg = widget.selected
+        ? theme.colorScheme.primary
+        : _hovered
+        ? theme.colorScheme.onSurface
+        : theme.colorScheme.onSurfaceVariant;
+    final bg = widget.selected
+        ? theme.colorScheme.primary.withValues(alpha: 0.12)
+        : _hovered
+        ? theme.colorScheme.surfaceContainerHigh
+        : Colors.transparent;
+    return Semantics(
+      button: true,
+      selected: widget.selected,
+      label: widget.label,
+      child: MouseRegion(
+        onEnter: (_) => setState(() => _hovered = true),
+        onExit: (_) => setState(() => _hovered = false),
+        cursor: SystemMouseCursors.click,
+        child: GestureDetector(
+          onTap: widget.onTap,
+          child: AnimatedContainer(
+            duration: ChainMotion.fast,
+            padding: const EdgeInsets.symmetric(
+              horizontal: ChainSpace.md,
+              vertical: 6,
+            ),
+            decoration: BoxDecoration(
+              color: bg,
+              borderRadius: BorderRadius.circular(ChainRadius.sm),
+              border: Border.all(
+                color: widget.selected
+                    ? theme.colorScheme.primary.withValues(alpha: 0.3)
+                    : Colors.transparent,
+              ),
+            ),
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                if (widget.icon != null) ...[
+                  Icon(widget.icon, size: 14, color: fg),
+                  const SizedBox(width: ChainSpace.xs),
+                ],
+                Text(
+                  widget.label,
+                  style: theme.textTheme.labelMedium?.copyWith(
+                    fontWeight: widget.selected
+                        ? FontWeight.w600
+                        : FontWeight.w400,
+                    color: fg,
+                  ),
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}

lib/widgets/widgets.dart

@@ -11,6 +11,7 @@ export 'chain_delta_mark.dart';
 export 'chain_empty_state.dart';
 export 'chain_en_badge.dart';
 export 'chain_error_box.dart';
+export 'chain_segments.dart';
 export 'hub_load_error_view.dart';
 export 'chain_flow_output.dart';
 export 'chain_install_confirm.dart';