feat(todo): allow several in_progress todos at once

Remove the single-in_progress cap from todo_write execute validation and
the durable-log invariant so a task list can mirror genuinely parallel
work (concurrent subagents, background commands). Update the tool
description to instruct marking every actively worked task in_progress,
refresh the tool catalog and keyless snapshot expected outputs, and
record the decision in a new Agent Note superseding the original cap.

packages/todo/tool-todo/tests/invariant.spec.ts

@@ -17,11 +17,12 @@ function event(todos: unknown): SessionEvent {
 }
 
 describe('todo snapshot invariants', () => {
-  it('accepts a unique whole-list snapshot with one active item', async () => {
+  it('accepts a unique whole-list snapshot, including several active items', async () => {
     const ctx = await setup()
     expect(() => { ctx.emit('session/event', {} as Session, event([
       { content: 'Inspect state', status: 'completed' },
       { content: 'Apply fix', status: 'in_progress' },
+      { content: 'Watch background build', status: 'in_progress' },
       { content: 'Run checks', status: 'pending' },
     ])) }).not.toThrow()
   })
@@ -36,7 +37,6 @@ describe('todo snapshot invariants', () => {
     [[{ content: 'same', status: 'pending' }, { content: 'same', status: 'completed' }], /repeats content/],
     [[{ content: 'task', status: 42 }], /unknown status/],
     [[{ content: 'task', status: 'paused' }], /unknown status/],
-    [[{ content: 'one', status: 'in_progress' }, { content: 'two', status: 'in_progress' }], /at most one/],
   ])('rejects an incoherent durable todo snapshot', async (todos, message) => {
     const ctx = await setup()
     expect(() => { ctx.emit('session/event', {} as Session, event(todos)) }).toThrow(message)

packages/todo/tool-todo/tests/tool-todo.spec.ts

@@ -122,10 +122,27 @@ describe('dsh-tool-todo', () => {
     expect(result.isError).toBe(true)
   })
 
+  it('accepts several in_progress items at once (parallel work)', async () => {
+    const ctx = await setup()
+    const agent = agentWithSession('parallel')
+    const todos: TodoItem[] = [
+      { content: 'run subagent a', status: 'in_progress' },
+      { content: 'run subagent b', status: 'in_progress' },
+      { content: 'merge results', status: 'pending' },
+    ]
+    const result = await callTodo(ctx, { todos }, { agent })
+    expect(result.isError).toBe(false)
+    if (result.isError) throw new Error('expected todo_write success')
+    expect(result.value).toEqual({
+      todos,
+      counts: { pending: 1, inProgress: 2, completed: 0 },
+    })
+    expect(agent.session.events.findLast(e => e.type === 'todo/write')!.data.todos).toEqual(todos)
+  })
+
   it.each([
     { label: 'empty content', todos: [{ content: '   ', status: 'pending' }], fragment: 'non-empty' },
     { label: 'duplicate content', todos: [{ content: 'dup', status: 'pending' }, { content: 'dup', status: 'completed' }], fragment: 'duplicate' },
-    { label: 'two in_progress', todos: [{ content: 'a', status: 'in_progress' }, { content: 'b', status: 'in_progress' }], fragment: 'in_progress' },
   ])('rejects $label as an isError result', async ({ todos, fragment }) => {
     const ctx = await setup()
     const result = await callTodo(ctx, { todos })