KUJO THE COURSETHE KUJO COURSE
Build 4: Bounded native automation
Where you are
Complete lessons 22–27 before starting. Write your own implementation first, then compare it with the tested solution. Review how each version handles input, effects, and failure.
Goal and acceptance contract
Read a contained fixture, run a controlled process, call a local HTTP fixture, and write a structured result.
The fixture response is successful, process output is complete, and work/automation.json contains the intended input. Removing an allowance fails at that boundary. The in-memory SQLite check returns one deterministic row.
Plan the boundary
Write down the input, output, and failure states before changing code. Decide which values are required and which may be absent. Keep calculations separate from printing so tests can assert their return values.
The loopback exception is deliberate and limited to this local fixture. Production outbound calls should select an approved external endpoint and apply --deny-private-net. The process example targets macOS/Linux /usr/bin/printf; configure a reviewed equivalent on Windows.
Do not grant more authority just to make a test pass. Compare the failed operation with the required inputs and allowed effects, then check every acceptance criterion.
Implementation milestones
1. Implement the smallest pure calculation with a normal and an empty-input case.
2. Add the input boundary and reject malformed values before any required effects.
3. Add the output contract and inspect it independently of the computation.
4. Run a deliberate failure and confirm both the status and the reason.
5. Preserve the source, runtime version, and test result as evidence.
Run the comparison
Clone the standalone course repository and run from its root unless the command changes directory. Create the ignored work directory before file-output exercises. Use Kujo 1.3.1.
node scripts/http-fixture.mjs
# In a second terminal, from the course root:
KUJO_ALLOW_PRIVATE_NETWORK_DESTINATIONS=1 kujo run --untrusted --allow-fs-read --allow-fs-write --allow-process-exec --allow-net-client projects/native/main.kujo
kujo run --untrusted --allow-database projects/native/database.kujo
The project verifier runs the local HTTP fixture server, these comparisons, and additional failure cases.
Break it deliberately
Remove a required input or allowance, alter an expected value, or supply a malformed record. Identify whether the failure happened during parsing, input validation, capability checking, execution, or evaluation. Fix the cause of the failure, then rerun the test.
A negative test must fail for the intended reason. A missing import does not prove that a validator rejected bad input. Check and retain the diagnostic.
Extend it
Replace the fixed local endpoint only as an explicit live opt-in. Validate its response, keep a finite timeout, deny private destinations, and preserve the offline fixture as the default suite.
Review before continuing
Explain the input contract, the authority required, and what proves success. Point to the test that rejects an incorrect result. Identify the finite bound on work. For concurrent or AI code, explain who owns completion and when a result may be accepted.
Keep this build and its tests for regression checks as you progress.
Comparison source
Download the entrypoint. The complete project, modules, fixtures, and tests are in the course repository.
# Run from the course root. Controlled loopback HTTP is an integration fixture.
let input_text := trim(read_file_beneath("fixtures", "input.txt", 1024))
let process := spawn_process(["/usr/bin/printf", "%s", input_text], {"timeout_ms": 2000, "max_output_bytes": 1024, "inherit_env": false})
assert_equal(process.success, true)
assert_equal(process.stdout_truncated, false)
let response := http_get("http://127.0.0.1:4190/health")
print(to_json(response))
let receipt := {"schema": "course.automation/v1", "input": input_text, "process_ok": process.success}
write_file("work/automation.json", to_json(receipt), true)
print(to_json(receipt))