fix timeline weirdness with zero extents

lib/controllers/room_chat.dart

@@ -3,7 +3,6 @@ import "dart:math";
 
 import "package:collection/collection.dart";
 import "package:fast_immutable_collections/fast_immutable_collections.dart";
-import "package:flutter/foundation.dart";
 import "package:flutter_riverpod/flutter_riverpod.dart";
 import "package:fluttertagger/fluttertagger.dart";
 import "package:nexus/controllers/attachment.dart";
@@ -84,14 +83,6 @@ class RoomChatController(final ChatParams info)
           .where((rowId) => room.events[rowId]?.threadRoot == null)
           .toIList();
 
-      // TODO: remove, debugging replies not showing
-      debugPrint(
-        "[timeline] build ${info.roomId}: "
-        "syncedTail=${room.timeline.entries.sortedBy<num>((entry) => entry.key).reversed.take(5).map((entry) => "${entry.key}:${entry.value}").toList()} "
-        "clientSticky=${room.clientSticky.toList()} "
-        "chatTail=${timeline.reversed.take(5).toList()}",
-      );
-
       if (info.contextualEvent == null ||
           timeline.contains(info.contextualEvent)) {
         ref.watch(
@@ -465,11 +456,6 @@ class RoomChatController(final ChatParams info)
 
   /// Shows [event], which was just sent, until it comes down sync.
   void addSent(Event? event) {
-    // TODO: remove, debugging replies not showing
-    debugPrint(
-      "[timeline] addSent: rowId=${event?.rowId} eventId=${event?.eventId} "
-      "alreadySynced=${ref.read(RoomsController.provider)[info.roomId]?.timeline.values.contains(event?.rowId)}",
-    );
     if (event case final event?) {
       ref
           .read(RoomsController.provider.notifier)

lib/helpers/hooks/chat_scroll.dart

@@ -9,14 +9,6 @@ import "package:nexus/models/room_chat.dart";
 
 typedef JumpToEvent = Future<void> Function(int rowId);
 
-/// Identifies the row for the event with [rowId], so it can be found to
-/// scroll to it, and keeps its element when rows are added before it.
-final class EventRowKey extends GlobalKey {
-  EventRowKey(this.rowId) : super.constructor();
-
-  final int rowId;
-}
-
 final class ChatScroll({
   required final IList<int> historyRows,
   required final IList<int> liveRows,
@@ -28,7 +20,7 @@ final class ChatScroll({
 
   required final JumpToEvent jumpToEvent,
   required final Future<void> Function() jumpToBottom,
-  required final EventRowKey Function(int eventRowId) keyFor,
+  required final GlobalKey Function(int eventRowId) keyFor,
 }) {
   factory use({
     required AsyncValue<RoomChat?> controllerData,
@@ -50,9 +42,9 @@ final class ChatScroll({
     final scrollController = useScrollController();
     final centerKey = useMemoized(GlobalKey.new);
 
-    final itemKeys = useMemoized(() => <int, EventRowKey>{}, []);
-    EventRowKey keyFor(int eventRowId) =>
-        itemKeys.putIfAbsent(eventRowId, () => EventRowKey(eventRowId));
+    final itemKeys = useMemoized(() => <int, GlobalKey>{}, []);
+    GlobalKey keyFor(int eventRowId) =>
+        itemKeys.putIfAbsent(eventRowId, GlobalKey.new);
 
     useEffect(() {
       if (anchorId.value == null) {
@@ -109,13 +101,6 @@ final class ChatScroll({
       final anchorIndex = items.indexOf(anchor);
 
       final historyLength = anchorIndex == -1 ? items.length : anchorIndex + 1;
-      // TODO: remove, debugging replies not showing
-      debugPrint(
-        "[timeline] split: anchor=$anchor anchorIndex=$anchorIndex "
-        "length=${items.length} "
-        "historyTail=${items.take(historyLength).toList().reversed.take(3).toList()} "
-        "live=${items.skip(historyLength).toList()}",
-      );
       return (
         history: items.take(historyLength).toIList().reversed.toIList(),
         live: items.skip(historyLength).toIList(),
@@ -128,27 +113,13 @@ final class ChatScroll({
     void updateAtBottom() {
       if (!hookContext.mounted || !scrollController.hasClients) return;
 
-      final position = scrollController.position;
-      final isAtBottom = position.extentBefore <= 0;
-      if (isAtBottom != atBottom.value) {
-        // TODO: remove, debugging replies not showing
-        debugPrint(
-          "[timeline] atBottom: $isAtBottom pixels=${position.pixels} "
-          "min=${position.minScrollExtent} anchor=${anchorId.value} "
-          "live=${split.live.length}",
-        );
-        atBottom.value = isAtBottom;
-      }
+      final isAtBottom = scrollController.position.extentBefore <= 0;
+      if (isAtBottom != atBottom.value) atBottom.value = isAtBottom;
     }
 
     useEffect(() {
       final previous = previousLastRowId.value;
       previousLastRowId.value = lastRowId;
-      // TODO: remove, debugging replies not showing
-      debugPrint(
-        "[timeline] lastRowId: previous=$previous last=$lastRowId "
-        "atBottom=${atBottom.value} contextualEvent=${contextualEvent.value}",
-      );
 
       if (previous == null || lastRowId == null || previous == lastRowId) {
         return null;
@@ -156,11 +127,6 @@ final class ChatScroll({
       if (!atBottom.value || contextualEvent.value != null) return null;
 
       WidgetsBinding.instance.addPostFrameCallback((_) {
-        // TODO: remove, debugging replies not showing
-        debugPrint(
-          "[timeline] re-anchoring to $lastRowId "
-          "hasClients=${scrollController.hasClients}",
-        );
         if (!scrollController.hasClients) return;
 
         anchorId.value = lastRowId;

lib/widgets/room_chat/chat_timeline.dart

@@ -25,7 +25,10 @@ class const ChatTimeline({
     int? previousEventRowId, {
     required Key key,
   }) => HighlightWrapper(
-    EventRenderer(
+    // To work around an AWFUL SuperSliverList bug
+    ConstrainedBox(
+      constraints: const BoxConstraints(minHeight: 0.01),
+      child: EventRenderer(
         eventRowId,
         previousEventRowId: previousEventRowId,
         roomId: chat.roomId,
@@ -36,20 +39,11 @@ class const ChatTimeline({
         readReceiptsChat: chat,
         threadRoot: chat.threadRoot,
       ),
+    ),
     key: key,
     isHighlighted: scroll.highlightedEvent == eventRowId,
   );
 
-  /// Where the row with [key] now is in [rows], so its element moves with it
-  /// when rows are added before it, rather than being rebuilt by index.
-  int? indexOf(IList<int> rows, Key key) => switch (key) {
-    EventRowKey(:final rowId) => switch (rows.indexOf(rowId)) {
-      -1 => null,
-      final index => index,
-    },
-    _ => null,
-  };
-
   @override
   Widget build(BuildContext context) => LayoutBuilder(
     builder: (context, constraints) => TweenAnimationBuilder(
@@ -76,7 +70,6 @@ class const ChatTimeline({
 
             SuperSliverList.builder(
               itemCount: scroll.liveRows.length,
-              findChildIndexCallback: (key) => indexOf(scroll.liveRows, key),
               itemBuilder: (_, index) => eventRow(
                 scroll.liveRows[index],
                 index > 0
@@ -89,8 +82,6 @@ class const ChatTimeline({
             SuperSliverList.builder(
               key: scroll.centerKey,
               itemCount: scroll.historyRows.length,
-              findChildIndexCallback: (key) =>
-                  indexOf(scroll.historyRows, key),
               itemBuilder: (_, index) => eventRow(
                 scroll.historyRows[index],
                 scroll.historyRows.getOrNull(index + 1),