dock Claude's task list above the composer (T-308)

Claude's TodoWrite checklist was invisible. Add a TaskItem/TaskStatus
model + a latest-wins parser (taskListFrom) that reads the most recent
TodoWrite tool call (it replaces the whole list each time), and a compact
display-only ClaudeTaskDock pinned between the conversation and the
composer: collapsed to "N tasks · M done" + the current in-progress item,
expandable to the full checklist with per-item status glyphs + a11y
labels. Hidden when there are no tasks. Parser + widget tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/claude/src/task_list.dart

@@ -0,0 +1,53 @@
+/// Claude's working task list, modelled from the conversation for the docked
+/// task view (T-308).
+///
+/// Claude tracks tasks with the `TodoWrite` tool, which **replaces the whole
+/// list** on each call — so the current state is simply the todos of the most
+/// recent `TodoWrite`. This is a latest-wins snapshot, not an append log; older
+/// `TodoWrite` calls are superseded.
+library;
+
+import 'package:clide/builtin/claude/src/transcript_reader.dart';
+
+enum TaskStatus { pending, inProgress, completed }
+
+class TaskItem {
+  const TaskItem({required this.text, required this.status});
+
+  final String text;
+  final TaskStatus status;
+
+  @override
+  bool operator ==(Object other) => other is TaskItem && other.text == text && other.status == status;
+
+  @override
+  int get hashCode => Object.hash(text, status);
+}
+
+/// The current task list — the todos of the most recent `TodoWrite` tool call,
+/// or empty if Claude hasn't written one this session.
+List<TaskItem> taskListFrom(List<ConversationItem> items) {
+  for (var i = items.length - 1; i >= 0; i--) {
+    final it = items[i];
+    if (it is! AssistantToolUse || it.name != 'TodoWrite') continue;
+    final raw = it.input['todos'];
+    if (raw is! List) return const [];
+    return [
+      for (final t in raw)
+        if (t is Map)
+          TaskItem(
+            // `content` is the canonical label; `activeForm` is the present-tense
+            // variant TodoWrite also carries — fall back to it, then to empty.
+            text: (t['content'] ?? t['activeForm'] ?? '').toString(),
+            status: _statusFrom(t['status']),
+          ),
+    ];
+  }
+  return const [];
+}
+
+TaskStatus _statusFrom(Object? raw) => switch (raw) {
+      'in_progress' => TaskStatus.inProgress,
+      'completed' => TaskStatus.completed,
+      _ => TaskStatus.pending,
+    };