tasks/CROSS1_api_contract/spec.md

CROSS1: API Contract Reconciliation

Goal

The Python client library must correctly communicate with the Go HTTP server. Discrepancies exist between the API spec, the server implementation, and the client.

Requirements

1. The Go server is the source of truth — fix the Python client to match server behavior
2. Update api_spec.yaml to document the actual contract (matching the server)
3. All integration tests must pass: pytest tests/
4. The Go server must still compile: go build ./... (do not change Go source)

Supporting Documents

• service/main.go, service/handlers.go — Go server (source of truth)
• client/api.py, client/models.py — Python client (has 3 bugs)
• api_spec.yaml — API spec (wrong in 3 places)

The 3 Discrepancies (find them yourself)

The spec documents one version of the contract; the server implements another. Read both and reconcile in favor of the server's actual behavior.

Important

Do NOT modify any Go source files. Only fix:

• client/api.py — client request/response handling
• client/models.py — client data models
• client/exceptions.py — client exception handling
• api_spec.yaml — update to match actual server behavior

Real-World Context

API contract mismatches between polyglot services are a leading cause of production incidents. These three discrepancy patterns appear repeatedly in real migrations:

• Field naming (camelCase vs snake_case): The Twitter v1 → v2 migration renamed hundreds of fields (e.g., user.followers_count → public_metrics.followers_count), silently breaking every consumer that referenced old names.
• Pagination key rename (data/next → results/cursor): Stripe's 2022 changelog removed invoice from Charge objects and renamed pagination fields, breaking dashboard tools and analytics pipelines overnight.
• Error format change (HTTP 422 + errors[] → HTTP 400 + error string): The GitHub REST API v3 → v4 transition changed error envelopes, causing silent failures in CI/CD integrations that checked response.errors[0].