Classify failures without retrying everything

Separate a repairable outage from a broken request.

Type: Build Languages: Go Stage: 2 of 4 Prerequisites: Stage 1 and HTTP status-code classes. Time: ~2 hours

What you build

Implement ClassifyStatus(status) with three outcomes. A 2xx response succeeds; 429 and 5xx permit fallback; all other valid codes are terminal. Integers outside 100 through 599 are invalid.

A 401 usually means the configured credential needs repair. Sending the same request to several providers can hide that mistake, so this project stops. A 503 indicates that a provider cannot serve the request right now, so another configured provider may help.

Worked example

Follow statuses [503, 200]: classify the first as retry, then the second as success. Follow [401, 200]: the 401 is terminal and the second provider is never contacted. A 307 is also terminal because the request layer refuses redirects.

This routing policy visits each provider at most once. It does not sleep for Retry-After, retry the same endpoint, or promise that a timed-out generation was never billed.

Implement the contract

func ClassifyStatus(status int) (string, error)

Validate the numeric range first, then test success, then the two retry conditions. Do not use status >= 400 as the retry rule: it would include malformed requests and authentication failures.

Run your work

From the repository root, initialize once; the grader preserves existing workspace files:

python3 scripts/project_test.py llm-gateway-with-fallbacks --init /tmp/llm-gateway-with-fallbacks-work
python3 scripts/project_test.py llm-gateway-with-fallbacks --stage 2 --path /tmp/llm-gateway-with-fallbacks-work --strict

Your implementation belongs in stage2.go in that workspace. Provided adapters call those learner functions; they do not import the reference solution. Stage tests include cases separate from the Orchard demonstration.

Inspect and extend

Predict the outcomes for 204, 301, 408, 429, 500 and 600. In this policy, 408 is terminal. If you choose to retry it in a future extension, write the new contract and side-effect assumptions before changing the implementation.

Go standard-library reference. The runnable core uses only Go's standard library. External model calls are optional and do not run during ordinary grading.