Keep dropped-out signals as MISSING rows; clear the nav bar in the mark sheet

A signal absent from the latest state now stays listed (from the last
envelope seen on this gateway) and renders as missing, distinct from
null and stale as BOUNDARY.md requires; rows no longer jump.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/boundary.dart

@@ -39,6 +39,10 @@ class Boundary extends ChangeNotifier {
   String detail = 'not started';
   Map<String, dynamic>? hello;
   Map<String, dynamic> signals = {};
+
+  /// Last envelope of every signal this gateway has sent. A name here but not in
+  /// [signals] is missing right now — distinct from null and stale.
+  final Map<String, Map<String, dynamic>> seen = {};
   DateTime? lastState;
   DateTime? lastMessage;
 
@@ -75,6 +79,7 @@ class Boundary extends ChangeNotifier {
   /// Change the target; the current connection is dropped and the loop reconnects.
   void retarget(String newUrl) {
     url = newUrl;
+    seen.clear();
     _ws?.close();
   }
 
@@ -144,6 +149,9 @@ class Boundary extends ChangeNotifier {
         }
       case 'state':
         signals = Map<String, dynamic>.from(m['signals'] as Map);
+        signals.forEach((k, v) {
+          if (v is Map) seen[k] = Map<String, dynamic>.from(v);
+        });
         lastState = DateTime.now();
       case 'ack':
         final id = m['id'] as String?;

lib/main.dart

@@ -1,6 +1,8 @@
 // Yukart display — starter. A text readout of whatever svc-gw sends, proving the
 // boundary contract before anything is drawn (initial plan, step 1).
 
+import 'dart:math';
+
 import 'package:flutter/material.dart';
 
 import 'boundary.dart';
@@ -142,7 +144,7 @@ class SignalList extends StatelessWidget {
     if (b.state != LinkState.up) {
       return const Center(child: Text('No link to the Orin'));
     }
-    if (b.signals.isEmpty) {
+    if (b.seen.isEmpty) {
       return Center(
         child: Text(
           'Connected — the Orin is sending no vehicle state\n(source: ${b.hello?['source'] ?? '?'})',
@@ -150,24 +152,41 @@ class SignalList extends StatelessWidget {
         ),
       );
     }
-    final names = b.signals.keys.toList()..sort();
+    // Rows stay put: a signal that drops out is shown as missing, not removed.
+    final names = b.seen.keys.toList()..sort();
     return ListView(
       padding: const EdgeInsets.all(12),
       children: [
-        for (final n in names) SignalTile(name: n, envelope: Map<String, dynamic>.from(b.signals[n] as Map)),
+        for (final n in names)
+          b.signals[n] is Map
+              ? SignalTile(name: n, envelope: Map<String, dynamic>.from(b.signals[n] as Map))
+              : SignalTile(name: n, envelope: b.seen[n]!, missing: true),
       ],
     );
   }
 }
 
-/// Known-without-value, stale and fresh each look different: all three are normal in a car.
+/// Missing, known-without-value, stale and fresh each look different: all four are normal in a car.
 class SignalTile extends StatelessWidget {
-  const SignalTile({super.key, required this.name, required this.envelope});
+  const SignalTile({super.key, required this.name, required this.envelope, this.missing = false});
   final String name;
+
+  /// The current envelope, or the last one seen when [missing] (only its unit is used then).
   final Map<String, dynamic> envelope;
+  final bool missing;
 
   @override
   Widget build(BuildContext context) {
+    if (missing) {
+      return ListTile(
+        title: Text(name, style: const TextStyle(fontFamily: 'monospace', color: Colors.grey)),
+        subtitle: const Text('MISSING · not in the latest state', style: TextStyle(color: Colors.redAccent)),
+        trailing: Text.rich(TextSpan(children: [
+          const TextSpan(text: '?', style: TextStyle(fontSize: 34, color: Colors.grey)),
+          TextSpan(text: '  ${envelope['unit'] ?? ''}', style: const TextStyle(fontSize: 16, color: Colors.grey)),
+        ])),
+      );
+    }
     final v = envelope['value'];
     final quality = envelope['quality'] as String? ?? 'ok';
     final stale = quality != 'ok';
@@ -227,6 +246,8 @@ Future<void> showMarkSheet(BuildContext context, Boundary b) {
   final custom = TextEditingController();
   return showModalBottomSheet(
     context: context,
+    isScrollControlled: true,
+    useSafeArea: true,
     builder: (ctx) {
       void send(String text) {
         if (text.trim().isEmpty) return;
@@ -235,7 +256,8 @@ Future<void> showMarkSheet(BuildContext context, Boundary b) {
       }
 
       return Padding(
-        padding: EdgeInsets.fromLTRB(16, 16, 16, 16 + MediaQuery.of(ctx).viewInsets.bottom),
+        // Clear the keyboard when it is up, the navigation bar when it is not.
+        padding: EdgeInsets.fromLTRB(16, 16, 16, 16 + max(MediaQuery.of(ctx).viewInsets.bottom, MediaQuery.of(ctx).viewPadding.bottom)),
         child: Column(mainAxisSize: MainAxisSize.min, crossAxisAlignment: CrossAxisAlignment.stretch, children: [
           Text('Stamp into the recording', style: Theme.of(ctx).textTheme.titleMedium),
           const SizedBox(height: 8),

test/boundary_test.dart

@@ -91,4 +91,22 @@ void main() {
     await b.stop();
     await gw.server.close(force: true);
   });
+
+  test('a signal that drops out stays known as missing', () async {
+    final gw = FakeGateway();
+    await gw.start();
+    final b = Boundary(gw.url)..start();
+    await until(() => b.state == LinkState.up);
+    Map<String, dynamic> env(num v) => {'timestamp': 0, 'monotonic': 0, 'value': v, 'unit': 'x'};
+    gw.sockets.first.add(jsonEncode({'t': 'state', 'seq': 1, 'signals': {'a': env(1), 'b': env(2)}}));
+    await until(() => b.signals.length == 2);
+    gw.sockets.first.add(jsonEncode({'t': 'state', 'seq': 2, 'signals': {'a': env(3)}}));
+    await until(() => b.signals.length == 1);
+    expect(b.seen.keys, containsAll(['a', 'b']));
+    expect(b.signals.containsKey('b'), isFalse);
+    b.retarget(gw.url);
+    expect(b.seen, isEmpty);
+    await b.stop();
+    await gw.server.close(force: true);
+  });
 }