[chat] adding plan/update plan blocks for threads

[visyat]

Adding basic post, edit, and task update operations for thread plans – unlocks the plan/task blocks in Slack for agent threads (status updates).

const plan = new Plan({ initialMessage: "Starting..." });
await thread.post(plan);

const result = await agent.generate({
  toolChoice: "required",
  prompt: message.text,
  onStepFinish: async (step) => {
    const { title: stepTitle, details: stepDetails } =
      getStepTaskTitleAndDetails(step);
    if (step.finishReason === "tool-calls") {
      // Single addTask: marks current complete and adds next in one edit (no flash).
      await plan.addTask({
        title: stepTitle,
        children: stepDetails.length > 0 ? stepDetails : undefined,
      });
    } else {
      await plan.updateTask({
        status: "complete",
        output: stepDetails.length > 0 ? stepDetails : undefined,
      });
    }
  },
  onFinish: async () => {
    await plan.complete({
      completeMessage: "AI finished",
    });
  },
});

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, Comment, Open in v0	Mar 6, 2026 10:56pm
chat-sdk-nextjs-chat	Ready	Preview, Comment, Open in v0	Mar 6, 2026 10:56pm

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[haydenbleasel]

@cramforce approved and merged @visyat's branch changes, resolved your comments, updated against main