feat: add per-channel HTTP transport controls

relaykit/dto/channel_settings.go

@@ -17,6 +17,38 @@ type ChannelSettings struct {
 	PassThroughBodyEnabled bool   `json:"pass_through_body_enabled,omitempty"`
 	SystemPrompt           string `json:"system_prompt,omitempty"`
 	SystemPromptOverride   bool   `json:"system_prompt_override,omitempty"`
+	// HTTPProtocol controls outbound HTTP version negotiation for this channel.
+	// Accepted values: "", "auto" (default), "http1".
+	HTTPProtocol string `json:"http_protocol,omitempty"`
+	// HTTP2ConnectionShards spreads HTTP/2 traffic across N independent transports
+	// (1-8). Zero/unset means 1. Ignored when HTTPProtocol is "http1".
+	HTTP2ConnectionShards int `json:"http2_connection_shards,omitempty"`
+}
+
+const (
+	HTTPProtocolAuto         = "auto"
+	HTTPProtocolHTTP1        = "http1"
+	MaxHTTP2ConnectionShards = 8
+)
+
+// ValidateHTTPTransport validates save-time HTTP transport channel settings.
+func (s *ChannelSettings) ValidateHTTPTransport() error {
+	if s == nil {
+		return nil
+	}
+	protocol := strings.ToLower(strings.TrimSpace(s.HTTPProtocol))
+	switch protocol {
+	case "", HTTPProtocolAuto, HTTPProtocolHTTP1:
+	default:
+		return fmt.Errorf("invalid http_protocol: %s", s.HTTPProtocol)
+	}
+	if s.HTTP2ConnectionShards < 0 || s.HTTP2ConnectionShards > MaxHTTP2ConnectionShards {
+		return fmt.Errorf("invalid http2_connection_shards: %d", s.HTTP2ConnectionShards)
+	}
+	if protocol == HTTPProtocolHTTP1 && s.HTTP2ConnectionShards > 1 {
+		return fmt.Errorf("http2_connection_shards must be 1 when http_protocol is http1")
+	}
+	return nil
 }
 
 type VertexKeyType string

relaykit/dto/channel_settings_test.go

@@ -1,6 +1,7 @@
 package dto
 
 import (
+	"encoding/json"
 	"regexp"
 	"testing"
 
@@ -519,3 +520,61 @@ func TestAdvancedCustomValidateAlphaSearchConverterPath(t *testing.T) {
 		})
 	}
 }
+
+func TestChannelSettingsHTTPTransportJSONRoundTrip(t *testing.T) {
+	legacy := `{"proxy":"http://127.0.0.1:8080","force_format":true}`
+	var settings ChannelSettings
+	require.NoError(t, json.Unmarshal([]byte(legacy), &settings))
+	assert.Equal(t, "http://127.0.0.1:8080", settings.Proxy)
+	assert.True(t, settings.ForceFormat)
+	assert.Empty(t, settings.HTTPProtocol)
+	assert.Zero(t, settings.HTTP2ConnectionShards)
+
+	encoded, err := json.Marshal(settings)
+	require.NoError(t, err)
+	assert.NotContains(t, string(encoded), "http_protocol")
+	assert.NotContains(t, string(encoded), "http2_connection_shards")
+
+	explicit := ChannelSettings{
+		Proxy:                 "socks5://127.0.0.1:1080",
+		HTTPProtocol:          HTTPProtocolHTTP1,
+		HTTP2ConnectionShards: 1,
+	}
+	encoded, err = json.Marshal(explicit)
+	require.NoError(t, err)
+	assert.Contains(t, string(encoded), `"http_protocol":"http1"`)
+
+	var decoded ChannelSettings
+	require.NoError(t, json.Unmarshal(encoded, &decoded))
+	assert.Equal(t, explicit.HTTPProtocol, decoded.HTTPProtocol)
+	assert.Equal(t, 1, decoded.HTTP2ConnectionShards)
+
+	sharded := ChannelSettings{HTTP2ConnectionShards: 4}
+	encoded, err = json.Marshal(sharded)
+	require.NoError(t, err)
+	assert.Contains(t, string(encoded), `"http2_connection_shards":4`)
+	assert.NotContains(t, string(encoded), "http_protocol")
+}
+
+func TestChannelSettingsValidateHTTPTransport(t *testing.T) {
+	require.NoError(t, (&ChannelSettings{}).ValidateHTTPTransport())
+	require.NoError(t, (&ChannelSettings{HTTPProtocol: "AUTO"}).ValidateHTTPTransport())
+	require.NoError(t, (&ChannelSettings{HTTPProtocol: "http1"}).ValidateHTTPTransport())
+	require.NoError(t, (&ChannelSettings{HTTP2ConnectionShards: 8}).ValidateHTTPTransport())
+
+	err := (&ChannelSettings{HTTPProtocol: "http2"}).ValidateHTTPTransport()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "http_protocol")
+
+	err = (&ChannelSettings{HTTP2ConnectionShards: -1}).ValidateHTTPTransport()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "http2_connection_shards")
+
+	err = (&ChannelSettings{HTTP2ConnectionShards: 9}).ValidateHTTPTransport()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "http2_connection_shards")
+
+	err = (&ChannelSettings{HTTPProtocol: "http1", HTTP2ConnectionShards: 2}).ValidateHTTPTransport()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "http2_connection_shards")
+}