feat(relay): hosted-tool conversion fidelity, reasoning normalization, and billing usage integrity (#7137)

* feat(relaykit): preserve hosted tools across conversions

- add protocol-neutral hosted-tool DTOs, conversion metadata, and loss policies
- bridge citations, grounding metadata, and hosted-tool stream lifecycles
- document the public conversion behavior and channel policy controls

* refactor(relaykit): normalize reasoning and thinking intent

- centralize provider-neutral reasoning intent, effort, and budget mappings
- parse model suffixes at the host entry boundary while preserving provider-owned tails
- keep adaptive Claude thinking and explicit zero-token compatibility consistent

* fix(billing): preserve authoritative usage across relay hops

- carry native BillingUsage sidecars through direct and streamed protocol bridges
- merge partial and terminal usage monotonically with safe fallback settlement
- retain cache metadata, penultimate usage, and per-call Gemini tool surcharges

* feat(relay): bridge Responses with Claude and Gemini protocols

- add direct request, response, and stream converters across supported relay formats
- expose Claude count_tokens and Chat-to-Responses compatibility endpoints
- carry conversion diagnostics through the host while retaining the curated public goldens

* fix(relay): wire relaykit conversions into host channels

- connect handlers, adaptors, and channel settings to the standalone conversion layer
- keep model mapping, pricing identity, retries, and provider-specific suffix behavior aligned
- ignore local audit artifacts and retain focused public regression coverage

relay/convert_request_error_test.go

@@ -0,0 +1,72 @@
+package relay
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/QuantumNous/new-api/common"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
+	"github.com/QuantumNous/new-api/relaykit/dto"
+	"github.com/QuantumNous/new-api/relaykit/types"
+	"github.com/QuantumNous/new-api/service"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptInSafeToolLossRejectedAsBadRequestWithAdminDiagnostics(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	c, _ := gin.CreateTestContext(httptest.NewRecorder())
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+
+	info := &relaycommon.RelayInfo{
+		OriginModelName: "gpt-4o",
+		ChannelMeta: &relaycommon.ChannelMeta{
+			UpstreamModelName: "gpt-4o",
+			ChannelOtherSettings: dto.ChannelOtherSettings{
+				ToolLossPolicy: string(types.ConversionLossPolicySafe),
+			},
+		},
+	}
+
+	tools, err := common.Marshal([]map[string]any{{"codeExecution": map[string]any{}}})
+	require.NoError(t, err)
+	req := &dto.GeminiChatRequest{
+		Contents: []dto.GeminiChatContent{
+			{Role: "user", Parts: []dto.GeminiPart{{Text: "run this"}}},
+		},
+		Tools: tools,
+	}
+
+	result, convErr := service.ConvertRequest(c, info, types.RelayFormatOpenAI, req)
+	require.Error(t, convErr)
+	var loss *types.ConversionLossError
+	require.ErrorAs(t, convErr, &loss)
+	require.NotEmpty(t, loss.Diagnostics)
+	require.NotNil(t, result)
+
+	apiErr := newConvertRequestFailedError(c, info, convErr)
+	require.NotNil(t, apiErr)
+	assert.Equal(t, http.StatusBadRequest, apiErr.StatusCode)
+	assert.Equal(t, types.ErrorCodeConvertRequestFailed, apiErr.GetErrorCode())
+	assert.True(t, types.IsSkipRetryError(apiErr))
+
+	diagnostics := info.ConversionDiagnostics()
+	require.NotEmpty(t, diagnostics)
+	assert.True(t, hasHostDiagnosticCode(diagnostics, "unsupported_hosted_tool"))
+
+	other := service.GenerateTextOtherInfo(c, info, 1, 1, 1, 0, 0, 0, 1)
+	adminInfo, ok := other["admin_info"].(map[string]interface{})
+	require.True(t, ok)
+	require.Contains(t, adminInfo, "conversion_diagnostics")
+}
+
+func hasHostDiagnosticCode(diagnostics []types.ConversionDiagnostic, code string) bool {
+	for _, diagnostic := range diagnostics {
+		if diagnostic.Code == code {
+			return true
+		}
+	}
+	return false
+}