Merge FB-08: reflow HUD row widgets on hide/show

# Conflicts:
#	docs/feedback/FB-08-hud-reflow-on-hide.md

docs/feedback/FB-08-hud-reflow-on-hide.md

@@ -1,6 +1,6 @@
 # FB-08 — HUD widgets reflow to fill the gap when one is hidden
 
-**Depends on** — · **Size** M · **Status** Not started
+**Depends on** — · **Size** M · **Status** Done
 
 ## Goal
 Hiding a HUD metric must resize the remaining widgets in its row to fill the empty
@@ -136,3 +136,22 @@ metric starts at, only how a row's members redistribute space among themselves w
 one of them is hidden or shown. Sequence FB-09 after this ticket merges, since both
 touch `HudLayoutController`/`HudWidgetLayout` and a large simultaneous diff in both is
 harder to review and merge than one after the other.
+
+## Outcome
+Implemented `_reflowRow` in `lib/src/hud/hud_layout_controller.dart` exactly as
+specified in the Design section, and wired it into `setVisible` using the toggled
+metric's `current.row` (its row before the toggle when hiding, its row after
+`defaultFor`/`nextFreeSlot` placement when showing) — no deviation from the design.
+
+Added four tests to `test/hud_layout_controller_test.dart` covering the four
+acceptance-criteria scenarios: hiding one of four same-row metrics reflows the
+remaining three to fill the row with no gap; hiding a metric alone in its row leaves
+every other metric's `col`/`row`/`colSpan` untouched; showing a previously-hidden
+metric into a row with an existing member reflows that row so their `colSpan`s sum to
+`hudGridColumns`; and toggling a metric in one row leaves a different row's members'
+`col`/`colSpan` unchanged.
+
+`flutter analyze` stayed clean (only pre-existing, unrelated info-level lint notices in
+`lib/src/crash/crash_reporter.dart` and `lib/src/tiles/map_connectivity.dart`, neither
+touched by this ticket). `flutter test` is green with a final count of **416 tests**
+(412 baseline + 4 new), no regressions.

lib/src/hud/hud_layout_controller.dart

@@ -67,7 +67,30 @@ class HudLayoutController extends StateNotifier<Map<HudMetric, HudWidgetLayout>>
         rowSpan: current.rowSpan,
       );
     }
-    state = {...state, metric: current.copyWith(visible: visible)};
+    final updated = {...state, metric: current.copyWith(visible: visible)};
+    state = _reflowRow(updated, current.row);
+  }
+
+  /// Spreads every visible widget in [row] evenly across the full grid width,
+  /// left to right in their existing column order. A widget whose row has no other
+  /// visible member is left alone -- there is nothing to redistribute.
+  Map<HudMetric, HudWidgetLayout> _reflowRow(
+    Map<HudMetric, HudWidgetLayout> layouts,
+    int row,
+  ) {
+    final members = layouts.values.where((l) => l.visible && l.row == row).toList()
+      ..sort((a, b) => a.col.compareTo(b.col));
+    if (members.length < 2) return layouts;
+    final baseSpan = hudGridColumns ~/ members.length;
+    final extra = hudGridColumns % members.length;
+    final result = Map<HudMetric, HudWidgetLayout>.from(layouts);
+    var col = 0;
+    for (var i = 0; i < members.length; i++) {
+      final span = baseSpan + (i < extra ? 1 : 0);
+      result[members[i].metric] = members[i].copyWith(col: col, colSpan: span);
+      col += span;
+    }
+    return result;
   }
 
   Future<void> persist() async => _config?.setHudLayout(state);

test/hud_layout_controller_test.dart

@@ -110,6 +110,80 @@ void main() {
       }
     });
 
+    test('hiding one of four same-row metrics reflows the remaining three to fill '
+        'the row with no gap', () async {
+      final controller = HudLayoutController(await freshConfig());
+
+      controller.setVisible(HudMetric.avgSpeed, false);
+
+      final remaining = [HudMetric.speed, HudMetric.distance, HudMetric.elapsedTime]
+          .map((m) => controller.state[m]!)
+          .toList()
+        ..sort((a, b) => a.col.compareTo(b.col));
+      final totalSpan = remaining.fold<int>(0, (sum, l) => sum + l.colSpan);
+      expect(totalSpan, hudGridColumns);
+      // baseSpan = 4 ~/ 3 = 1, extra = 1 -- the first (leftmost) member absorbs it.
+      expect(remaining[0].colSpan, 2);
+      expect(remaining[1].colSpan, 1);
+      expect(remaining[2].colSpan, 1);
+      expect(controller.state[HudMetric.avgSpeed]!.visible, isFalse);
+    });
+
+    test('hiding a metric whose row has no other visible member leaves every '
+        'other metric untouched', () async {
+      final controller = HudLayoutController(await freshConfig());
+      // Row 4 is unused by any default layout -- move speed there alone.
+      controller.updatePosition(HudMetric.speed, 0, 4);
+
+      final others = {
+        for (final m in HudMetric.values.where((m) => m != HudMetric.speed))
+          m: controller.state[m]!,
+      };
+
+      controller.setVisible(HudMetric.speed, false);
+
+      for (final entry in others.entries) {
+        final after = controller.state[entry.key]!;
+        expect(after.col, entry.value.col, reason: '${entry.key} col changed');
+        expect(after.row, entry.value.row, reason: '${entry.key} row changed');
+        expect(after.colSpan, entry.value.colSpan,
+            reason: '${entry.key} colSpan changed');
+      }
+    });
+
+    test('showing a previously-hidden metric back into a row with existing '
+        'members reflows that row to fit it', () async {
+      final controller = HudLayoutController(await freshConfig());
+
+      // maxSpeed and movingTime both default to row 2, hidden, at adjacent columns.
+      controller.setVisible(HudMetric.maxSpeed, true);
+      controller.setVisible(HudMetric.movingTime, true);
+
+      final maxSpeed = controller.state[HudMetric.maxSpeed]!;
+      final movingTime = controller.state[HudMetric.movingTime]!;
+      expect(maxSpeed.row, movingTime.row,
+          reason: 'test setup assumes both land in the same row');
+      expect(maxSpeed.colSpan + movingTime.colSpan, hudGridColumns);
+    });
+
+    test('toggling a metric in one row leaves a different row\'s members '
+        'untouched', () async {
+      final controller = HudLayoutController(await freshConfig());
+      final row2Before = {
+        for (final m in [HudMetric.maxSpeed, HudMetric.movingTime, HudMetric.elevationGain])
+          m: controller.state[m]!,
+      };
+
+      controller.setVisible(HudMetric.avgSpeed, false);
+
+      for (final entry in row2Before.entries) {
+        final after = controller.state[entry.key]!;
+        expect(after.col, entry.value.col, reason: '${entry.key} col changed');
+        expect(after.colSpan, entry.value.colSpan,
+            reason: '${entry.key} colSpan changed');
+      }
+    });
+
     test('persist writes the current state to Config', () async {
       final config = await freshConfig();
       final controller = HudLayoutController(config);