feat(todo): comments on a task (ADR 0033, D36)

Plain text with links, written, edited and deleted in the task's sheet,
counted on its row. They are sealed in `task_comment`, the task they belong
to with them, and go with their task.

Whats-New: Comments: write on a task, edit or delete what you wrote, and open its links.
Whats-New-De: Kommentare: Schreibe zu einer Aufgabe, bearbeite oder lösche es und öffne Links darin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/lib/l10n/app_de.arb

@@ -55,6 +55,15 @@
   "filterMatches": "{count, plural, =1{1 Aufgabe passt} other{{count} Aufgaben passen}}",
   "filterNotRead": "Nicht verstanden bei „{near}“",
   "filterNotReadEnd": "Die Abfrage endet zu früh",
+  "commentsTitle": "Kommentare",
+  "commentAdd": "Kommentar schreiben",
+  "commentSend": "Kommentar senden",
+  "commentMenu": "Kommentarmenü",
+  "commentEdit": "Kommentar bearbeiten",
+  "commentCopy": "Text kopieren",
+  "commentDelete": "Kommentar löschen",
+  "commentDeleteTitle": "Kommentar löschen?",
+  "commentEdited": "{when}, bearbeitet",
   "labelsTitle": "Labels",
   "labelsNone": "Noch keine Labels.",
   "labelsNoneSet": "Keine Labels",

apps/todo/halkyon_todo_flutter/lib/l10n/app_en.arb

@@ -115,6 +115,23 @@
   "@filterNotReadEnd": {
     "description": "The filter editor when its query stops before it is complete."
   },
+  "commentsTitle": "Comments",
+  "commentAdd": "Add a comment",
+  "commentSend": "Send comment",
+  "commentMenu": "Comment menu",
+  "commentEdit": "Edit comment",
+  "commentCopy": "Copy text",
+  "commentDelete": "Delete comment",
+  "commentDeleteTitle": "Delete the comment?",
+  "commentEdited": "{when}, edited",
+  "@commentEdited": {
+    "description": "When a comment was written, once it was changed.",
+    "placeholders": {
+      "when": {
+        "type": "String"
+      }
+    }
+  },
   "labelsTitle": "Labels",
   "labelsNone": "No labels yet.",
   "labelsNoneSet": "No labels",

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations.dart

@@ -430,6 +430,60 @@ abstract class AppLocalizations {
   /// **'This query ends too soon'**
   String get filterNotReadEnd;
 
+  /// No description provided for @commentsTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Comments'**
+  String get commentsTitle;
+
+  /// No description provided for @commentAdd.
+  ///
+  /// In en, this message translates to:
+  /// **'Add a comment'**
+  String get commentAdd;
+
+  /// No description provided for @commentSend.
+  ///
+  /// In en, this message translates to:
+  /// **'Send comment'**
+  String get commentSend;
+
+  /// No description provided for @commentMenu.
+  ///
+  /// In en, this message translates to:
+  /// **'Comment menu'**
+  String get commentMenu;
+
+  /// No description provided for @commentEdit.
+  ///
+  /// In en, this message translates to:
+  /// **'Edit comment'**
+  String get commentEdit;
+
+  /// No description provided for @commentCopy.
+  ///
+  /// In en, this message translates to:
+  /// **'Copy text'**
+  String get commentCopy;
+
+  /// No description provided for @commentDelete.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete comment'**
+  String get commentDelete;
+
+  /// No description provided for @commentDeleteTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete the comment?'**
+  String get commentDeleteTitle;
+
+  /// When a comment was written, once it was changed.
+  ///
+  /// In en, this message translates to:
+  /// **'{when}, edited'**
+  String commentEdited(String when);
+
   /// No description provided for @labelsTitle.
   ///
   /// In en, this message translates to:

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_de.dart

@@ -203,6 +203,35 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get filterNotReadEnd => 'Die Abfrage endet zu früh';
 
+  @override
+  String get commentsTitle => 'Kommentare';
+
+  @override
+  String get commentAdd => 'Kommentar schreiben';
+
+  @override
+  String get commentSend => 'Kommentar senden';
+
+  @override
+  String get commentMenu => 'Kommentarmenü';
+
+  @override
+  String get commentEdit => 'Kommentar bearbeiten';
+
+  @override
+  String get commentCopy => 'Text kopieren';
+
+  @override
+  String get commentDelete => 'Kommentar löschen';
+
+  @override
+  String get commentDeleteTitle => 'Kommentar löschen?';
+
+  @override
+  String commentEdited(String when) {
+    return '$when, bearbeitet';
+  }
+
   @override
   String get labelsTitle => 'Labels';
 

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_en.dart

@@ -203,6 +203,35 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get filterNotReadEnd => 'This query ends too soon';
 
+  @override
+  String get commentsTitle => 'Comments';
+
+  @override
+  String get commentAdd => 'Add a comment';
+
+  @override
+  String get commentSend => 'Send comment';
+
+  @override
+  String get commentMenu => 'Comment menu';
+
+  @override
+  String get commentEdit => 'Edit comment';
+
+  @override
+  String get commentCopy => 'Copy text';
+
+  @override
+  String get commentDelete => 'Delete comment';
+
+  @override
+  String get commentDeleteTitle => 'Delete the comment?';
+
+  @override
+  String commentEdited(String when) {
+    return '$when, edited';
+  }
+
   @override
   String get labelsTitle => 'Labels';
 

apps/todo/halkyon_todo_flutter/lib/src/app/todo_dependencies.dart

@@ -11,6 +11,8 @@ import 'package:halkyon_todo_client/halkyon_todo_client.dart'
 import 'package:halkyon_todo_flutter/l10n/app_localizations.dart';
 import 'package:halkyon_todo_flutter/src/core/privacy/sync_content_key_gateway.dart';
 import 'package:halkyon_todo_flutter/src/core/privacy/todo_keys.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/data/comment_repository.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/data/sync_comment_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/filter/data/filter_repository.dart';
 import 'package:halkyon_todo_flutter/src/feature/filter/data/sync_filter_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/label/data/label_repository.dart';
@@ -67,6 +69,9 @@ class TodoPerson(
   /// Their filters, sealed and synced (D35).
   required final FilterRepository filters,
 
+  /// Their comments on tasks, sealed and synced (D36).
+  required final CommentRepository comments,
+
   /// Their settings of Todo's (Upcoming's Display), sealed and synced.
   required final SettingsRepository settings,
 
@@ -405,9 +410,11 @@ Future<TodoPerson> _openPersonData(
   final projects = ProjectRepository(SyncProjectGateway(db, sync), keys);
   final sections = SectionRepository(SyncSectionGateway(db, sync), keys);
   final settings = SettingsRepository(SyncSettingsGateway(db, sync), keys);
+  final comments = CommentRepository(SyncCommentGateway(db, sync), keys);
   final tasks = TaskRepository(
     SyncTaskGateway(db, sync),
     keys,
+    onDeleted: comments.deleteOn,
     automaticReminder: () async => (await settings.read()).reminders.automatic,
   );
   final labels = LabelRepository(SyncLabelGateway(db, sync), keys);
@@ -429,6 +436,7 @@ Future<TodoPerson> _openPersonData(
     tasks: tasks,
     labels: labels,
     filters: filters,
+    comments: comments,
     settings: settings,
     reminders: reminders,
     notifications: notifications,
@@ -442,6 +450,7 @@ Future<TodoPerson> _openPersonData(
         await tasks.dispose();
         await labels.dispose();
         await filters.dispose();
+        await comments.dispose();
         await settings.dispose();
         await sync.dispose();
         await db.close();

apps/todo/halkyon_todo_flutter/lib/src/feature/comment/data/comment_payload.dart

@@ -0,0 +1,32 @@
+import 'dart:typed_data';
+
+import 'package:halkyon_todo_flutter/src/core/sealed/json_payload.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/model/comment.dart';
+
+/// The schema of a comment's payload this app writes and reads.
+const commentSchemaVersion = 1;
+
+/// [content] as its row's payload, before sealing.
+ByteData encodeComment(CommentContent content) =>
+    encodeJson(commentSchemaVersion, {
+      'taskId': content.taskId,
+      'text': content.text,
+      'writtenAt': content.writtenAt.toUtc().toIso8601String(),
+      'editedAt': ?content.editedAt?.toUtc().toIso8601String(),
+    });
+
+/// The comment [payload] holds, opened; null for one it can't read.
+CommentContent? decodeComment(ByteData payload) => decodeJson(
+  payload,
+  version: commentSchemaVersion,
+  name: 'Comment',
+  read: (json) => CommentContent(
+    taskId: json['taskId']! as String,
+    text: json['text']! as String,
+    writtenAt: DateTime.parse(json['writtenAt']! as String),
+    editedAt: switch (json['editedAt']) {
+      final String at => DateTime.parse(at),
+      _ => null,
+    },
+  ),
+);

apps/todo/halkyon_todo_flutter/lib/src/feature/comment/data/comment_repository.dart

@@ -0,0 +1,48 @@
+import 'package:halkyon_todo_flutter/src/core/privacy/todo_keys.dart';
+import 'package:halkyon_todo_flutter/src/core/sealed/sealed_row_gateway.dart';
+import 'package:halkyon_todo_flutter/src/core/sealed/sealed_rows.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/data/comment_payload.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/model/comment.dart';
+
+/// The person's comments on their tasks (ADR 0033, D36), each sealed with
+/// their key for its row (D5, [SealedRows]); which task one belongs to is
+/// sealed with it.
+class CommentRepository(final SealedRowGateway _gateway, final TodoKeys _keys) {
+  late final _rows = SealedRows<CommentContent>(
+    _gateway,
+    _keys,
+    table: 'task_comment',
+    encode: encodeComment,
+    decode: decodeComment,
+  );
+
+  /// Fires when the comments changed, here or on another device.
+  Stream<void> get changes => _rows.changes;
+
+  /// Every comment, oldest first.
+  Future<List<StoredComment>> all() async => [
+    for (final (:id, :content) in await _rows.all()) StoredComment(id, content),
+  ];
+
+  /// Keeps a new comment and returns its ID; throws [KeysMissing] where
+  /// this device can't seal.
+  Future<String> add(CommentContent content) => _rows.insert(content);
+
+  Future<void> update(String id, CommentContent content) =>
+      _rows.update(id, content);
+
+  /// Deletes the comments [ids].
+  Future<void> delete(Iterable<String> ids) => _rows.delete(ids);
+
+  /// Deletes the comments on the tasks [taskIds], which are gone.
+  Future<void> deleteOn(Set<String> taskIds) async {
+    final comments = await all();
+    await _rows.delete([
+      for (final comment in comments)
+        if (taskIds.contains(comment.content?.taskId)) comment.id,
+    ]);
+  }
+
+  /// Closes what it holds open.
+  Future<void> dispose() => _rows.dispose();
+}

apps/todo/halkyon_todo_flutter/lib/src/feature/comment/data/sync_comment_gateway.dart

@@ -0,0 +1,99 @@
+import 'dart:typed_data';
+
+import 'package:halkyon_app/halkyon_app.dart';
+import 'package:halkyon_todo_client/halkyon_todo_client.dart' as protocol;
+import 'package:halkyon_todo_flutter/src/core/sealed/sealed_row_gateway.dart';
+import 'package:serverpod_offline_sync_client/offline_sync.dart';
+
+/// The person's comments on their local database ([SealedRowGateway]), which the
+/// sync engine keeps in step with their other devices.
+class SyncCommentGateway(
+  final OfflineSyncDatabaseSession _db,
+  final SyncService _sync,
+) implements SealedRowGateway {
+  @override
+  Future<List<SealedRow>> rows() async => [
+    for (final row in await protocol.TaskComment.db.find(
+      _db,
+      orderBy: (t) => t.id,
+    ))
+      (
+        id: row.id!.uuid,
+        envelope: (keyId: row.keyId, nonce: row.nonce, payload: row.payload),
+      ),
+  ];
+
+  @override
+  Future<void> insert(SealedRow row) async {
+    await protocol.TaskComment.db.insertRow(
+      _db,
+      protocol.TaskComment(
+        id: protocol.UuidValue.withValidation(row.id),
+        keyId: row.envelope.keyId,
+        nonce: row.envelope.nonce,
+        payload: row.envelope.payload,
+      ),
+    );
+    _sync.requestSync();
+  }
+
+  @override
+  Future<void> update(String id, Envelope envelope) async {
+    if (await protocol.TaskComment.db.findById(
+          _db,
+          protocol.UuidValue.withValidation(id),
+        )
+        case final row?) {
+      // Only the named columns change (ADR 0001, rule 1).
+      await protocol.TaskComment.db.updateRow(
+        _db,
+        row.copyWith(
+          keyId: envelope.keyId,
+          nonce: envelope.nonce,
+          payload: envelope.payload,
+        ),
+        columns: (t) => [t.keyId, t.nonce, t.payload],
+      );
+      _sync.requestSync();
+    }
+  }
+
+  @override
+  Future<void> delete(Iterable<String> ids) async {
+    final uuids = <protocol.UuidValue>{
+      for (final id in ids) protocol.UuidValue.withValidation(id),
+    };
+    if (uuids.isEmpty) {
+      return;
+    }
+    await _db.db.transaction((transaction) async {
+      // Blanked first (ADR 0002, rule 2): the instance keeps deleted rows as
+      // they last were, until the space goes.
+      for (final row in await protocol.TaskComment.db.find(
+        _db,
+        where: (t) => t.id.inSet(uuids),
+        transaction: transaction,
+      )) {
+        await protocol.TaskComment.db.updateRow(
+          _db,
+          protocol.TaskComment(
+            id: row.id,
+            spaceId: row.spaceId,
+            payload: ByteData(0),
+          ),
+          columns: (t) => [t.keyId, t.nonce, t.payload],
+          transaction: transaction,
+        );
+      }
+      await protocol.TaskComment.db.deleteWhere(
+        _db,
+        where: (t) => t.id.inSet(uuids),
+        transaction: transaction,
+      );
+    });
+    _sync.requestSync();
+  }
+
+  @override
+  Stream<void> get remoteChanges => _sync.merges;
+}

apps/todo/halkyon_todo_flutter/lib/src/feature/comment/model/comment.dart

@@ -0,0 +1,50 @@
+import 'package:equatable/equatable.dart';
+
+/// A comment on the task [taskId] (ADR 0033, D36): plain [text], with links
+/// shown as such, [writtenAt], and [editedAt] once it was changed. Markdown
+/// can come later without touching what is kept.
+final class const CommentContent({
+  required final String taskId,
+  required final String text,
+  required final DateTime writtenAt,
+  final DateTime? editedAt,
+}) with Equatable {
+  @override
+  List<Object?> get props => [taskId, text, writtenAt, editedAt];
+}
+
+/// A comment as kept: its [id], and [content] null where it doesn't open.
+final class const StoredComment(final String id, final CommentContent? content)
+    with Equatable {
+  @override
+  List<Object?> get props => [id, content];
+}
+
+/// A piece of a comment's text: the link it stands for, or plain text.
+typedef TextPiece = ({String text, Uri? url});
+
+final _link = RegExp(r'https?://[^\s<>"]+', caseSensitive: false);
+
+/// [text] cut into plain pieces and links: http and https alone, so that a
+/// comment can never start anything else on the device, and without the
+/// punctuation that ends a sentence after a link.
+List<TextPiece> linkPieces(String text) {
+  final pieces = <TextPiece>[];
+  var at = 0;
+  for (final match in _link.allMatches(text)) {
+    final found = match[0]!.replaceFirst(RegExp(r'[.,;:!?)\]]+$'), '');
+    final url = Uri.tryParse(found);
+    if (url == null || url.host.isEmpty) {
+      continue;
+    }
+    if (match.start > at) {
+      pieces.add((text: text.substring(at, match.start), url: null));
+    }
+    pieces.add((text: found, url: url));
+    at = match.start + found.length;
+  }
+  if (at < text.length) {
+    pieces.add((text: text.substring(at), url: null));
+  }
+  return pieces;
+}

apps/todo/halkyon_todo_flutter/lib/src/feature/comment/widget/task_comments.dart

@@ -0,0 +1,290 @@
+import 'dart:async';
+
+import 'package:clock/clock.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:halkyon_app/halkyon_app.dart';
+import 'package:halkyon_todo_flutter/l10n/app_localizations.dart';
+import 'package:halkyon_todo_flutter/src/app/todo_dependencies.dart';
+import 'package:halkyon_todo_flutter/src/core/widget/menu_entry.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/model/comment.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/bloc/todo_cubit.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/model/task.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/widget/task_texts.dart';
+import 'package:halkyon_ui/halkyon_ui.dart';
+import 'package:lucide_icons_flutter/lucide_icons.dart';
+import 'package:material_ui/material_ui.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+/// The key of the field writing a comment.
+const commentFieldKey = ValueKey('comment-field');
+
+/// The key of the button sending a comment.
+const commentSendKey = ValueKey('comment-send');
+
+/// The comments on the task [taskId] in its sheet (ADR 0033, D36): each with
+/// when it was written and a menu to edit, copy or delete it, its links
+/// opening in the browser, and a field to write one more.
+class const TaskComments({required final String taskId, super.key})
+    extends StatefulWidget {
+  @override
+  State<TaskComments> createState() => _TaskCommentsState();
+}
+
+class _TaskCommentsState() extends State<TaskComments> {
+  final _text = TextEditingController();
+
+  @override
+  void dispose() {
+    _text.dispose();
+    super.dispose();
+  }
+
+  Future<void> _send(TodoPerson todo) async {
+    final text = _text.text.trim();
+    if (text.isEmpty) {
+      return;
+    }
+    _text.clear();
+    setState(() {});
+    await todo.comments.add(
+      CommentContent(
+        taskId: widget.taskId,
+        text: text,
+        writtenAt: clock.now(),
+      ),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final theme = Theme.of(context);
+    final todo = PersonScope.of<TodoPerson>(context);
+    final comments = context.watch<TodoCubit>().state.commentsOn(widget.taskId);
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      children: [
+        Padding(
+          padding: const EdgeInsets.fromLTRB(16, 12, 16, 4),
+          child: Text(
+            comments.isEmpty
+                ? l10n.commentsTitle
+                : '${l10n.commentsTitle}  ${comments.length}',
+            style: theme.textTheme.titleSmall?.copyWith(
+              color: theme.colorScheme.onSurfaceVariant,
+            ),
+          ),
+        ),
+        for (final comment in comments) _Comment(comment: comment),
+        Padding(
+          padding: const EdgeInsets.fromLTRB(12, 4, 4, 8),
+          child: Row(
+            crossAxisAlignment: CrossAxisAlignment.end,
+            children: [
+              Expanded(
+                child: TextField(
+                  key: commentFieldKey,
+                  controller: _text,
+                  minLines: 1,
+                  maxLines: 6,
+                  textCapitalization: TextCapitalization.sentences,
+                  decoration: InputDecoration(hintText: l10n.commentAdd),
+                  onChanged: (_) => setState(() {}),
+                ),
+              ),
+              IconButton(
+                key: commentSendKey,
+                tooltip: l10n.commentSend,
+                icon: const Icon(LucideIcons.arrowUp),
+                onPressed: _text.text.trim().isEmpty
+                    ? null
+                    : () => unawaited(_send(todo)),
+              ),
+            ],
+          ),
+        ),
+      ],
+    );
+  }
+}
+
+class const _Comment({required final StoredComment comment})
+    extends StatelessWidget {
+  Future<void> _edit(BuildContext context, CommentContent content) async {
+    final todo = PersonScope.of<TodoPerson>(context);
+    final edited = await showDialog<String>(
+      context: context,
+      builder: (context) => _EditComment(text: content.text),
+    );
+    if (edited != null && edited.isNotEmpty && edited != content.text) {
+      await todo.comments.update(
+        comment.id,
+        CommentContent(
+          taskId: content.taskId,
+          text: edited,
+          writtenAt: content.writtenAt,
+          editedAt: clock.now(),
+        ),
+      );
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final theme = Theme.of(context);
+    final muted = theme.colorScheme.onSurfaceVariant;
+    final content = comment.content!;
+    final local = content.writtenAt.toLocal();
+    final when =
+        '${dayText(context, Day.of(local), Day.of(clock.now()))}, '
+        '${timeText(context, local.hour * 60 + local.minute)}';
+    final todo = PersonScope.of<TodoPerson>(context);
+    return Padding(
+      padding: const EdgeInsetsDirectional.only(start: 16, bottom: 4),
+      child: Row(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  content.editedAt == null ? when : l10n.commentEdited(when),
+                  style: theme.textTheme.bodySmall?.copyWith(color: muted),
+                ),
+                const SizedBox(height: 2),
+                _LinkedText(text: content.text),
+              ],
+            ),
+          ),
+          PopupMenuButton<VoidCallback>(
+            tooltip: l10n.commentMenu,
+            icon: const Icon(LucideIcons.ellipsis),
+            onSelected: (action) => action(),
+            itemBuilder: (context) => [
+              PopupMenuItem(
+                value: () => unawaited(_edit(context, content)),
+                child: MenuEntry(LucideIcons.pencil, l10n.commentEdit),
+              ),
+              PopupMenuItem(
+                value: () => unawaited(
+                  Clipboard.setData(ClipboardData(text: content.text)),
+                ),
+                child: MenuEntry(LucideIcons.copy, l10n.commentCopy),
+              ),
+              PopupMenuItem(
+                value: () async {
+                  if (await confirmDestructiveAction(
+                    context,
+                    title: l10n.commentDeleteTitle,
+                    message: content.text,
+                    confirmLabel: l10n.commentDelete,
+                  )) {
+                    await todo.comments.delete([comment.id]);
+                  }
+                },
+                child: MenuEntry(
+                  LucideIcons.trash2,
+                  l10n.commentDelete,
+                  destructive: true,
+                ),
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+/// [text] with its links underlined, a tap opening them in the browser.
+class const _LinkedText({required final String text}) extends StatefulWidget {
+  @override
+  State<_LinkedText> createState() => _LinkedTextState();
+}
+
+class _LinkedTextState() extends State<_LinkedText> {
+  final _taps = <TapGestureRecognizer>[];
+
+  void _release() {
+    for (final tap in _taps) {
+      tap.dispose();
+    }
+    _taps.clear();
+  }
+
+  @override
+  void dispose() {
+    _release();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    _release();
+    final link = TextStyle(
+      color: Theme.of(context).colorScheme.primary,
+      decoration: TextDecoration.underline,
+    );
+    return SelectableText.rich(
+      TextSpan(
+        children: [
+          for (final piece in linkPieces(widget.text))
+            switch (piece.url) {
+              final url? => TextSpan(
+                text: piece.text,
+                style: link,
+                recognizer: TapGestureRecognizer()
+                  ..onTap = () => unawaited(
+                    launchUrl(url, mode: LaunchMode.externalApplication),
+                  ),
+              ),
+              null => TextSpan(text: piece.text),
+            },
+        ],
+      ),
+    );
+  }
+}
+
+class const _EditComment({required final String text}) extends StatefulWidget {
+  @override
+  State<_EditComment> createState() => _EditCommentState();
+}
+
+class _EditCommentState() extends State<_EditComment> {
+  late final _text = TextEditingController(text: widget.text);
+
+  @override
+  void dispose() {
+    _text.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    return AlertDialog(
+      title: Text(l10n.commentEdit),
+      content: TextField(
+        controller: _text,
+        autofocus: true,
+        minLines: 1,
+        maxLines: 8,
+      ),
+      actions: [
+        TextButton(
+          onPressed: () => Navigator.of(context).pop(),
+          child: Text(MaterialLocalizations.of(context).cancelButtonLabel),
+        ),
+        FilledButton(
+          onPressed: () => Navigator.of(context).pop(_text.text.trim()),
+          child: Text(l10n.save),
+        ),
+      ],
+    );
+  }
+}

apps/todo/halkyon_todo_flutter/lib/src/feature/task/bloc/todo_cubit.dart

@@ -5,6 +5,7 @@ import 'package:equatable/equatable.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:halkyon_core/halkyon_core.dart';
 import 'package:halkyon_todo_flutter/src/app/todo_dependencies.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/model/comment.dart';
 import 'package:halkyon_todo_flutter/src/feature/filter/model/saved_filter.dart';
 import 'package:halkyon_todo_flutter/src/feature/label/model/label.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/model/stored_project.dart';
@@ -26,6 +27,9 @@ final class const TodoState({
   /// Their filters that open, in their order (D35).
   final List<StoredFilter> filters = const [],
 
+  /// Their comments that open, oldest first (D36).
+  final List<StoredComment> comments = const [],
+
   /// Their settings of Todo's, as at first until read.
   final TodoSettings settings = const TodoSettings(),
 
@@ -40,6 +44,12 @@ final class const TodoState({
       .map((project) => project.id)
       .firstOrNull;
 
+  /// The comments on the task [taskId], oldest first.
+  List<StoredComment> commentsOn(String taskId) => [
+    for (final comment in comments)
+      if (comment.content!.taskId == taskId) comment,
+  ];
+
   /// The project [id], opened; null for one gone or locked.
   StoredProject? projectOf(String id) => projects
       .where((project) => project.id == id && project.content != null)
@@ -63,6 +73,7 @@ final class const TodoState({
     tasks,
     labels,
     filters,
+    comments,
     settings,
     locked,
   ];
@@ -88,6 +99,7 @@ class TodoCubit(final TodoPerson _todo) extends Cubit<TodoState> {
       _todo.tasks.changes,
       _todo.labels.changes,
       _todo.filters.changes,
+      _todo.comments.changes,
       _todo.settings.changes,
     ]) {
       _subscriptions.add(changes.listen((_) => unawaited(_reads.run())));
@@ -101,6 +113,7 @@ class TodoCubit(final TodoPerson _todo) extends Cubit<TodoState> {
     final tasks = await _todo.tasks.all();
     final labels = await _todo.labels.all();
     final filters = await _todo.filters.all();
+    final comments = await _todo.comments.all();
     final settings = await _todo.settings.read();
     if (isClosed) {
       return;
@@ -122,6 +135,13 @@ class TodoCubit(final TodoPerson _todo) extends Cubit<TodoState> {
           for (final filter in filters)
             if (filter.content != null) filter,
         ]..sort((a, b) => a.content!.position.compareTo(b.content!.position)),
+        comments:
+            [
+              for (final comment in comments)
+                if (comment.content != null) comment,
+            ]..sort(
+              (a, b) => a.content!.writtenAt.compareTo(b.content!.writtenAt),
+            ),
         settings: settings,
         locked: [
           ...projects.map((row) => row.content),
@@ -129,6 +149,7 @@ class TodoCubit(final TodoPerson _todo) extends Cubit<TodoState> {
           ...tasks.map((row) => row.content),
           ...labels.map((row) => row.content),
           ...filters.map((row) => row.content),
+          ...comments.map((row) => row.content),
         ].where((content) => content == null).length,
       ),
     );

apps/todo/halkyon_todo_flutter/lib/src/feature/task/data/task_repository.dart

@@ -20,6 +20,9 @@ class TaskRepository(
 
   /// The person's automatic reminder, read as it is needed; none: never.
   final Future<int?> Function()? automaticReminder,
+
+  /// Told the tasks deleted, whose comments go with them (D36).
+  final Future<void> Function(Set<String> taskIds)? onDeleted,
 }) {
   late final _rows = SealedRows<TaskContent>(
     _gateway,
@@ -239,14 +242,14 @@ class TaskRepository(
   /// Deletes the task [id] with its sub-tasks, theirs too, together.
   Future<void> delete(String id) async {
     final tasks = await all();
-    await _rows.delete(_withDescendants({id}, tasks));
+    await _gone(_withDescendants({id}, tasks));
   }
 
   /// Deletes every task in the project [projectId] (or, given, only those
   /// in its section [sectionId]), with their sub-tasks, together.
   Future<void> deleteIn(String projectId, {String? sectionId}) async {
     final tasks = await all();
-    await _rows.delete(
+    await _gone(
       _withDescendants({
         for (final task in tasks)
           if (task.content case final content?
@@ -257,6 +260,11 @@ class TaskRepository(
     );
   }
 
+  Future<void> _gone(Set<String> ids) async {
+    await _rows.delete(ids);
+    await onDeleted?.call(ids);
+  }
+
   /// Closes what it holds open.
   Future<void> dispose() => _rows.dispose();
 

apps/todo/halkyon_todo_flutter/lib/src/feature/task/widget/task_sheet.dart

@@ -9,6 +9,7 @@ import 'package:halkyon_todo_flutter/src/app/todo_dependencies.dart';
 import 'package:halkyon_todo_flutter/src/app/todo_paths.dart';
 import 'package:halkyon_todo_flutter/src/core/privacy/todo_keys.dart';
 import 'package:halkyon_todo_flutter/src/core/widget/menu_entry.dart';
+import 'package:halkyon_todo_flutter/src/feature/comment/widget/task_comments.dart';
 import 'package:halkyon_todo_flutter/src/feature/location/model/task_location.dart';
 import 'package:halkyon_todo_flutter/src/feature/location/widget/location_picker.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/model/stored_project.dart';
@@ -906,6 +907,7 @@ class _TaskSheetState() extends State<_TaskSheet> {
               ],
             ),
           ),
+          _Box(child: TaskComments(taskId: task.id)),
         ],
       ),
     );

apps/todo/halkyon_todo_flutter/lib/src/feature/task/widget/task_tile.dart

@@ -108,6 +108,8 @@ class const TaskTile({
           '${subTasks.length}',
           muted,
         ),
+      if (state.commentsOn(task.id).length case final count when count > 0)
+        meta(LucideIcons.messageSquare, '$count', muted),
       for (final id in content.labelIds)
         if (labels[id] case final label?)
           meta(