Isso não é uma limitação do **FastAPI** , é parte do protocolo HTTP.

///

## Recapitulando

package configdump

import (
	"sort"
	"time"

	admin "github.com/envoyproxy/go-control-plane/envoy/admin/v3"
	route "github.com/envoyproxy/go-control-plane/envoy/config/route/v3"

	"istio.io/istio/pilot/pkg/util/protoconv"
	v3 "istio.io/istio/pilot/pkg/xds/v3"
)

// GetLastUpdatedDynamicRouteTime retrieves the LastUpdated timestamp of the
// most recently updated DynamicRouteConfig

- This code change fixes the bug that UDP services would trigger unnecessary LoadBalancer updates. The root cause is that a field not working for non-TCP protocols is considered.
  ref: https://github.com/kubernetes-sigs/cloud-provider-azure/pull/1090 ([#107981](https://github.com/kubernetes/kubernetes/pull/107981), [@lzhecheng](https://github.com/lzhecheng))

   * invoked after [connectStart].
   */
  open fun connectEnd(
    call: Call,
    inetSocketAddress: InetSocketAddress,
    proxy: Proxy,
    protocol: Protocol?,
  ) {
  }

  /**
   * Invoked when a connection attempt fails. This failure is not terminal if further routes are
   * available and failure recovery is enabled.
   *

        ":version",
        "HTTP/1.1",
        "connection",
        "close",
      )
    val request = Request.Builder().url("http://square.com/").build()
    val response = readHttp2HeadersList(headerBlock, Protocol.HTTP_2).request(request).build()
    val headers = response.headers
    assertThat(headers.size).isEqualTo(1)
    assertThat(headers.name(0)).isEqualTo(":version")
    assertThat(headers.value(0)).isEqualTo("HTTP/1.1")
  }

NAMESPACE          POD NAME                                             ADDRESS     NODE                  WAYPOINT                            PROTOCOL
bookinfo           bookinfo-productpage-istio-waypoint-5cdd6745d5-rc2gg 10.244.2.59 ambient-worker2       None                                TCP
bookinfo           details-v1-698d88b-dqrbr                             10.244.2.51 ambient-worker2       namespace-istio-waypoint            HBONE

Esta não é uma limitação do **FastAPI**, é parte do protocolo HTTP.

///

## Recapitulando

      val response =
        Response.Builder()
          .code(101)
          .message("OK")
          .request(Request.Builder().url(url).build())
          .headers(responseHeaders!!)
          .protocol(Protocol.HTTP_1_1)
          .build()
      webSocket =
        RealWebSocket(
          taskFaker.taskRunner,
          response.request,
          listener,
          random!!,

github.com/gogo/protobuf
https://github.com/gogo/protobuf
----------------------------------------------------------------
Copyright (c) 2013, The GoGo Authors. All rights reserved.

Protocol Buffers for Go with Gadgets

Go support for Protocol Buffers - Google's data interchange format

Copyright 2010 The Go Authors.  All rights reserved.
https://github.com/golang/protobuf

                        proxyProtocol:
                          description: The upstream PROXY protocol settings.
                          properties:
                            version:
                              description: |-
                                The PROXY protocol version to use.

                                Valid Options: V1, V2
                              enum: