MessageAugmentPower Scenario

Use a pipeline scenario to show how a power can enrich an inbound value step by step

Scenario

You want to enrich a message before it enters the main execution path:

  • add the current page title
  • add a source marker

This kind of pre-chain value enrichment is a strong fit for pipeline.

Example

import {
  Power,
  type PowerJsonObject,
  type PowerHooks,
} from "@downcity/city/power";

class MessageAugmentPower extends Power {
  readonly name = "message_augment";
  readonly title = "Message Augment";
  readonly description = "Adds extra fields to inbound message payloads.";

  readonly hooks: PowerHooks = {
    pipeline: {
      "chat.enrich_message": [
        async ({ value }) => {
          const body = value as PowerJsonObject;
          return {
            ...body,
            source: body.source || "web",
            pageTitle: body.pageTitle || "Untitled Page",
          };
        },
      ],
    },
  };
}

// City has registered message_augment and bound it to entry's Agent/Workspace.
const message = await city.powers.scope({ agent_id: agent.id, workspace_id: workspace.id }).pipeline<PowerJsonObject>("chat.enrich_message", {
  text: "Please summarize this page",
});

What this scenario is meant to teach

  • a pipeline receives one value and returns a new value
  • several powers can extend the same chain in sequence