perf: add HTTP connection pooling across providers and disable proxy buffering on SSE streams

internal/providers/helpers.go

@@ -5,10 +5,15 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"net"
+	"net/http"
 	"regexp"
 	"strings"
+	"time"
 
 	"gophergate/internal/models"
+
+	"github.com/go-resty/resty/v2"
 )
 
 var keySanitizeRegex = regexp.MustCompile(`(?i)(key|api_key|secret)=[^&]+`)
@@ -18,6 +23,34 @@ func SanitizeURL(rawURL string) string {
 	return keySanitizeRegex.ReplaceAllString(rawURL, "$1=REDACTED")
 }
 
+// Shared HTTP transport configured with high connection pooling, TCP keep-alive,
+// and HTTP/2 multiplexing to minimize latency when connecting to upstream LLM providers.
+var sharedHTTPTransport = &http.Transport{
+	Proxy: http.ProxyFromEnvironment,
+	DialContext: (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}).DialContext,
+	ForceAttemptHTTP2:     true,
+	MaxIdleConns:          200,
+	MaxIdleConnsPerHost:   50,
+	IdleConnTimeout:       90 * time.Second,
+	TLSHandshakeTimeout:   10 * time.Second,
+	ExpectContinueTimeout: 1 * time.Second,
+}
+
+// NewOptimizedRestyClient creates a resty client equipped with HTTP connection pooling.
+func NewOptimizedRestyClient(timeout time.Duration) *resty.Client {
+	httpClient := &http.Client{
+		Transport: sharedHTTPTransport,
+	}
+	client := resty.NewWithClient(httpClient)
+	if timeout > 0 {
+		client.SetTimeout(timeout)
+	}
+	return client
+}
+
 
 func sanitizeFunctionName(name string) string {
 	var sb strings.Builder