feat(tool-todo): add the model-facing todo_write tool

Add @deepseek-ai/dsh-tool-todo (a new packages/todo/ group): a model-facing
todo_write(todos: [{content, status}]) tool with whole-list-replace semantics.
Each call appends the full list as a todo/write event to the calling agent's
session log; the current list is the most recent such event (last-write-wins).
Single-owner — a non-agent caller is rejected. Beyond the schema's
type/required/enum checks, execute rejects empty/duplicate content and more than
one in_progress task, narrowing the loosely-typed args into a real TodoItem[].

Both UIs render off the existing session/event: the stdio UI prints a glyphed
checklist; the ACP bridge maps the list to a `plan` sessionUpdate (todosToPlan
synthesizes the priority ACP requires; status maps 1:1). Wired into the
coding-agent, acp-agent, and snapshot example configs with a system-prompt nudge.

Tests: unit (schema, validation, append/replace, no-agent rejection, presentCall,
HMR-safety, Loader export-shape guard), full-loop integration through the agent
loop, the ACP todosToPlan mapping + stream-update arm, the stdio render arm, and
a session/load replay that re-emits the plan. New-group TS wiring added to
tsconfig.base/json/build. RFC + a doc-inventory sweep (architecture, packages
README, AGENTS layout, cookbook group list, example READMEs) ship with it.

The todo-plan ACP snapshot scenario is recorded separately (needs an API key).

packages/support/ui-stdio/src/index.ts

@@ -110,6 +110,13 @@ export function createStdioChat(ctx: Context, config: Config, runtime: StdioRunt
       const { content } = event.data
       const text = content.filter(block => block.type === 'text').map(block => block.text).join('')
       output.write(`\n  [tool result] ${text}\n  `)
+    } else if (event.type === 'todo/write') {
+      if (inReasoning) output.write('\x1B[0m')
+      inReasoning = false
+      const glyph = (status: string): string =>
+        status === 'completed' ? '[x]' : status === 'in_progress' ? '[~]' : '[ ]'
+      const lines = event.data.todos.map(todo => `    ${glyph(todo.status)} ${todo.content}`).join('\n')
+      output.write(`\n  [todos]\n${lines}\n  `)
     }
   })
 

packages/support/ui-stdio/tests/ui-stdio.spec.ts

@@ -151,6 +151,35 @@ describe('createStdioChat rendering', () => {
     expect(out.text()).toContain('[tool result] file.txt')
   })
 
+  it('renders a todo/write session event as a glyphed checklist', async () => {
+    const { ctx, out } = await setup()
+    const session = {} as Session
+    ctx.emit('session/event', session, {
+      type: 'todo/write', seq: 1, time: 0,
+      data: { todos: [
+        { content: 'read the code', status: 'completed' },
+        { content: 'write the fix', status: 'in_progress' },
+        { content: 'run the tests', status: 'pending' },
+      ] },
+    } as SessionEvent)
+    const text = out.text()
+    expect(text).toContain('[todos]')
+    expect(text).toContain('[x] read the code')
+    expect(text).toContain('[~] write the fix')
+    expect(text).toContain('[ ] run the tests')
+  })
+
+  it('resets dim styling when a todo/write interrupts reasoning', async () => {
+    const { ctx, out } = await setup()
+    const agent = makeAgent('main')
+    ctx.emit('agent/stream-chunk', agent, 1, 0, { type: 'reasoning-delta', index: 0, text: 'r' })
+    ctx.emit('session/event', {} as Session, {
+      type: 'todo/write', seq: 1, time: 0,
+      data: { todos: [{ content: 'a task', status: 'pending' }] },
+    } as SessionEvent)
+    expect(out.text()).toContain('\x1B[2mr\x1B[0m')
+  })
+
   it('resets dim styling when a tool/call interrupts reasoning', async () => {
     const { ctx, out } = await setup()
     const agent = makeAgent('main')