Your AI Feature Doesn't Fail at the Model. It Fails at the Handoff

Description and use

Automation recipe: protect AI features from handoff failures using a FastAPI proxy that validates auth, limits payload size, streams responses, and is tested with boundary checks.

Problem

AI features often fail not because of the model but due to integration layers such as auth, payload limits, and streaming handling.

Outcome

The proxy successfully prevents handoff failures, ensuring the model never receives malformed requests and improving overall reliability.

Workflow

• Deploy a FastAPI proxy that checks auth header and message count.
• Configure the proxy to forward requests to the upstream model and stream responses back.
• Create a rehearsal script that sends test requests for missing auth, wrong token, oversized body, and happy path.
• Run the rehearsal script to verify each boundary returns the expected status code.
• Iterate on proxy logic until all tests pass.
• Integrate the proxy into the production stack.
• Monitor for boundary failures in production logs.

Evidence

The model had done its job flawlessly, and the handoff had not.

Source

Here is the smallest slice I could build that still crosses every boundary.

Source