Actions are backing tools the View can call. They are hidden from the model.

defineAction is defineTool with visibility: ["app"]. Same options as Tools.

get-forecast/actions.ts

import { z } from "zod";
import { defineAction } from "bitmcp";

export const refresh = defineAction({
  description: "Reload forecast points",
  input: z.object({ city: z.string() }),
  async execute({ city }) {
    return {
      city,
      summary: `Updated forecast for ${city}`,
      points: [
        { t: "Mon", temp: 70 },
        { t: "Tue", temp: 74 },
        { t: "Wed", temp: 71 },
      ],
    };
  },
});

Naming

get-forecast/
  tool.ts
  view.tsx
  actions.ts    export const refresh = defineAction(...)

Registered name: get-forecast.refresh.

From the View

get-forecast/view.tsx

callTool("get-forecast.refresh", { city: result.city });

Each call is a new stateless tools/call. Pass handles or ids explicitly when resuming work.