Post fetcher runtime tutorial

This tutorial shows what the UMA runtime layer owns around a pure service: validation, adapter selection, deterministic event ordering, and lifecycle evidence.

By Enrico Piovesan Updated June 22, 2026

Tutorial route

Use the links below to move through the tutorial sequence without dropping to the footer first.

Open source folder All UMA examples Previous: Feature Flag Evaluator Next: UMA Portability Lab

What you will learn

what belongs in service logic versus runtime logic
why validation should stop execution before side effects happen
how lifecycle metadata records the network.fetch adapter binding

Prerequisites

Rust 1.77 or newer
cargo
jq
Node.js and npm for TypeScript parity

Full tutorial

Enter the example
```
cd chapter-05-post-fetcher-runtime
```
List the guided labs
```
./scripts/list_labs.sh
```

Run the golden cloud host path

./scripts/run_lab.sh lab1-cloud-golden-path

Run fail-fast header validation

./scripts/run_lab.sh lab2-header-validation-fail-fast

Inspect adapter binding and wrappers

./scripts/run_lab.sh lab3-adapter-binding-and-wrappers

Verify Rust and TypeScript parity

./scripts/run_lab.sh lab4-rust-ts-parity

Run the chapter smoke path
```
./scripts/smoke_runtime_labs.sh
```

What to inspect

After each command, look for these proof points. They are the signals that connect the code example back to the UMA architecture claim.

output.events
lifecycle.bindings
final lifecycle.state

Acceptance check

The chapter-level validation path is:

./scripts/smoke_runtime_labs.sh

Return to the repository root for the final acceptance gate:

cd ..
./scripts/smoke_reader_paths.sh

Where to go next

Chapter 6 proves portability across native and WASI targets.

Open source folder All UMA examples Read Chapter 6: The Runtime Layer → Previous: Feature Flag Evaluator Next: UMA Portability Lab