Lesson 22.1822.18 Designing a hosted worker: the four disciplines

The design guide for everything before it. Its last table is a map of the whole chapter, best read after the Milestone 1 and 2 reading. Each discipline gets three answers: do you need it on a hosted platform, how you design it there, and where the lab builds it.

In everyday life. A company hires a contracting firm to staff its warehouse night shift. The firm supplies the workers, the forklifts and the building's security guard. The company still writes the job sheet each worker reads, sets the site rules, decides whether one worker or a crew with a supervisor does the job, and decides when each shift starts and who inspects the work. Hiring the firm removed the hiring and the equipment. It did not remove a single one of those decisions. In this concept, the firm is the hosting platform, and the job sheet, site rules, crew and shifts are the four disciplines.

What you will learn. What hosting does and does not decide for the four kinds of design that shape a worker, and how to write down who decided each part.

Why it matters. Hosting removes code, not decisions. What the worker sees, what limits it, how its work is split and what starts it are still yours to design.

One request, start to finish. Before the worker is sold, Brightline's controller asks the builder for one page: "How is this worker designed, and who decided each part?" The builder fills in one row per discipline:

1. What it sees (context): the worker contract's rules in the instructions, the invoice-triage skill for method, the connector's four tool descriptions, and one question per session. Decided with the AP expert (Task 1).
2. What surrounds it (harness): three file tools and the four read-only connector tools, everything else off, one open door on the network, connector tools on "allow" only after review, and a budget on every run. Decided by the builder, checked by check:agent-config (Tasks 2, 5, 6).
3. How the work is split (graph): one agent, in one session. No helpers yet, because nothing measured says they are needed. A month-end review may add an outcome (Task 21b).
4. Who prompts it next (loop): a person's question in the portal, or the morning schedule, a check by code, two rounds at most, and "needs review" after that (Task 18).

The controller reads the page and asks one more question: "So what did the platform decide?" The builder's answer: "Nothing on this page. It runs what the page says."

What does a hosted platform remove?

A hosted platform removes code, not design. Four kinds of design decide how a worker behaves: context (what it sees), harness (what surrounds it), graph (how its work is split) and loop (who prompts it next). On a hosted platform you design each one in configuration, files and your product, not in code you write yourself.

Figure 22.24. Hosting runs the machinery of each discipline. Every design decision is still yours.

What is each discipline, in one line?

Context: you put everything the worker reads there. Harness: the platform runs it, and you decide what it allows, with 21.9's five verbs, constrain, inform (give it what it needs to know), verify, correct and escalate (hand a decision to a person). Graph: split the work only when one agent is not enough, and say why. Loop: a worker people pay for is a loop, as 22.15 and 22.16 set out. The full design guide for each, with its questions and Brightline examples, is on the companion page. The map below gives one row per discipline.

What are the stages of a worker's life?

The four disciplines design the worker. Its whole life has eight stages. This chapter builds the first six, and starts the last two:

What do you design for each discipline?

Four more rows, for the topics in Beyond this chapter (a nervous system, an agent-to-agent protocol, scheduled coding-agent runs and vendor standing assistants), are on the companion page.

At work. In Lab 22, Task 21, Claude Code updates docs/deploy.md. Add one table to it, the controller's page: one row per discipline, what was decided, who decided it, and the file or check that holds the decision.

The operating rule: a hosted platform runs what your design says, and nothing more. Write the design down, one row per discipline, each held in a file or a check.

Part E in one minute

Add helpers, workflows, an advisor or an outcome only for a measured reason, and host the loop yourself only when a rule or a cost demands it (22.17). Hosting runs the machinery, but the context, the harness, the graph and the loop are still yours to design (22.18).

Now do Lab 22, Sitting 5 on the lab page: Tasks 20 and 21, and the optional Tasks 19 and 21b (about 1 hour 5 minutes, or 2 hours with both extensions). It ends with your reviewed pull request. Then come back for 22.19 and Check yourself.