Result Overrides

What it demonstrates

Result-override middleware intercepts the OUTPUT of a run and modifies it before it reaches the caller. The pattern is always the same: await call_next() to let the model (and inner middleware / tools) finish, then read and rewrite context.result. This is where you enrich answers, inject disclaimers, redact, or replace the response — without editing the agent’s instructions. Two layers can override and they nest: chat middleware sees a ChatResponse per model call; agent middleware wraps the whole run with an AgentResponse.

One real excerpt

@chat_middleware
async def disclaimer_middleware(context: ChatContext, call_next) -> None:
    await call_next()  # let the model produce its answer first
    if context.result is None:
        return
    original = context.result.text or ""
    context.result = ChatResponse(messages=[Message(
        role="assistant",
        contents=[f"{original}\n\n(Disclaimer: AI-generated, not financial advice.)"],
    )])

The gotcha

Override AFTER await call_next() — before it, context.result is still None, so always guard with if context.result is None: return. Replace by assigning a fresh response object: a ChatResponse for chat middleware, an AgentResponse for agent middleware. Agent middleware is outermost, so it sees whatever the chat layer already produced. For streaming runs (context.stream is True), the result is a ResponseStream — you don’t reassign text, you attach hooks like context.result.with_transform_hook(...). A Message is built from contents=[...], a list, not a bare string.

Azure / MAF mapping

Both @chat_middleware and @agent_middleware decorators register via Agent(..., middleware=[...]) over FoundryChatClient. Chat-level overrides run per model call; agent-level wraps the entire run, so a single response can carry both a disclaimer and an audit stamp.

Run it

uv run tutorial/02-agents/middleware/04_result_overrides.py — needs Foundry creds. Worked if the answer ends with a disclaimer and an [audited ✓] stamp.

Next: Exception Handling