Harness Engineering with Claude Code: workshop kit

Classroom material for the workshop. Two exercises and five labs, a sample repository for each lab, and the sheets to print. Every lab has step-by-step instructions in labs/, so you can also do it on your own.

The code accompanies chapters 4 to 7 of Harness Engineering with Claude Code (Packt, Alexio Cassani). It really runs: the Lab 5 suites run against the Lab 4 hooks, not against mock-ups.

Setup, now

git clone https://github.com/FairMind-Gen-AI-Studio/he-workshop.git
cd he-workshop
ls code kit
claude --version

Prerequisites

You need	For
claude (Claude Code), signed in	Labs 2, 3, 4
bash, git, jq	Labs 3, 4, 5
pnpm (corepack enable gives you one)	Lab 4
npx with prettier	Lab 4
python3 with pyyaml	Lab 5
docker and @devcontainers/cli	Lab 3, optional

No Docker? Lab 3 has a reading variant, open to anyone whose build fails too. The container is verified on Docker 28.3 for macOS; elsewhere it is untested ground.

Quick check:

for c in claude bash git jq pnpm npx python3 docker devcontainer; do
  printf '%-13s %s\n' "$c" "$(command -v $c || echo MISSING)"
done
python3 -c 'import yaml; print("pyyaml ok")'

The day

#	Activity	Time	Instructions	Where
1	Exercise 1: Your plateau	5'	labs/exercise-1.md	paper, kit/exercise-1.md
2	Lab 1: Diagnose a harness	20'	labs/lab-1.md	paper, kit/matrix-5x4.md
3	Exercise 2: Route a failure	3'	labs/exercise-2.md	paper, kit/exercise-2.md
4	Lab 2: A contract that changes behavior	30'	labs/lab-2.md	kit/lab2/, code/ch04/
5	Lab 3: Boundaries, as files	30'	labs/lab-3.md	code/ch05/
6	Lab 4: The enforcement layer	35'	labs/lab-4.md	code/ch06/
7	Lab 5: Watching the instruments fail	25'	labs/lab-5.md	code/ch07/

Every lab file has the same shape: goal, numbered steps with the exact commands, the output to expect, a "done when" checklist and a reset section that puts the repository back as you found it. Run every command from the repository root unless the step says otherwise.

What is inside

Folder	Lab	What it holds
labs/	all	Step-by-step instructions, one file per activity
kit/	1, 2, 3, 4	The printable sheets, the bloated CLAUDE.md in kit/lab2/, the settings merge in kit/lab3/, the sibling-hooks snippet in kit/lab4/
code/ch04/	2	A real repository contract: CLAUDE.md, rules, three skills, the nested layer in services/api/
code/ch05/	3	The personal deny floor, the dev container with an egress firewall, the domain allowlist
code/ch06/	4	Eight hooks: the gate classifier, the contrasting blocklist, the Stop orchestrator, the command log; plus a minimal pnpm project for the Stop gate to check
code/ch06-pristine/	5	An intact copy of the above. Do not touch it
code/ch07/	5	The adversarial suite for the hooks and the eval-set scorer

Every code/ folder has its own README with a file-by-file map.

code/ch06-pristine/ exists for a reason. The Lab 5 suite sends its payloads to the Lab 4 gate-aws-cli.sh. If it pointed at the copy you just changed, anyone who broke something in Lab 4 would see a red run that teaches nothing. It points at the intact copy instead.

License

The chapter code accompanies the book and is distributed with Packt's companion repository. The classroom material belongs to FairMind.