forgesight-fastapi

The FastAPI integration for ForgeSight. Three lines wire request↔run correlation, incoming-trace continuation, and flush-on-shutdown into any FastAPI / Starlette app — no per-handler instrumentation.

pip install forgesight-fastapi

from fastapi import FastAPI
from forgesight_fastapi import ForgeSightMiddleware, sdk_lifespan

app = FastAPI(lifespan=sdk_lifespan)        # configure() on startup, flush on shutdown
app.add_middleware(ForgeSightMiddleware)     # request → agent_run span, correlation

@app.post("/agents/pr-reviewer/run")
async def run(req: ReviewRequest):
    # Unchanged agent code. The run span is already open and bound to this request;
    # the agent's llm/tool/mcp calls nest under it automatically.
    return await pr_reviewer.run(req.task)

Compose with an existing lifespan:

from contextlib import asynccontextmanager
from forgesight_fastapi import sdk_lifespan

@asynccontextmanager
async def lifespan(app):
    async with sdk_lifespan(app):
        await connect_db()
        yield
        await close_db()

app = FastAPI(lifespan=lifespan)

What you get

• Request↔run link. The HTTP request and the agent run share a trace_id; the response carries the run_id (header x-forgesight-run-id), so "request X was slow" jumps straight to the run's span tree and cost.
• Distributed traces just work. An upstream traceparent is continued automatically — the agent service is a child span, not a new root. No propagation code in the app.
• Zero lost telemetry on deploy. sdk_lifespan calls force_flush() + shutdown() on the shutdown phase (which ASGI servers run on SIGTERM), with a bounded timeout so a wedged backend can't hang the deploy.
• Route-level metadata for free. The matched route template (/agents/{id}/run, not the raw path — bounded cardinality), method, and status land as span metadata (FR-5).
• Correct error mapping. 5xx ⇒ span ERROR + error.type; an unhandled exception is recorded and re-raised (FR-7); 4xx is recorded without erroring the span.

Implemented as pure ASGI (not BaseHTTPMiddleware) to avoid streaming/lifespan pitfalls. Request/response bodies are captured only when capture_content resolves true (P7).

Configuration

Constructor kwargs win over env / forgesight.yaml (integrations.fastapi).

License

Apache-2.0