diff --git a/backend/internal/pkg/apicompat/responses_namespace.go b/backend/internal/pkg/apicompat/responses_namespace.go
new file mode 100644
index 0000000000..a5549760c5
--- /dev/null
+++ b/backend/internal/pkg/apicompat/responses_namespace.go
@@ -0,0 +1,212 @@
+package apicompat
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+// ResponsesNamespaceName identifies a function child in a Responses namespace.
+// It aliases the chat bridge mapping so both native and bridged paths share one
+// namespace identity contract.
+type ResponsesNamespaceName = NamespacedToolName
+
+// FlattenResponsesNamespaces converts Codex private namespace declarations into
+// public Responses function tools and rewrites namespace-qualified request calls.
+func FlattenResponsesNamespaces(req map[string]any) (map[string]ResponsesNamespaceName, bool, error) {
+	return FlattenResponsesNamespacesExcept(req, nil)
+}
+
+// FlattenResponsesNamespacesExcept is FlattenResponsesNamespaces with a set of
+// service-owned namespace names that must remain native in the request.
+func FlattenResponsesNamespacesExcept(req map[string]any, preserved map[string]bool) (map[string]ResponsesNamespaceName, bool, error) {
+	if req == nil {
+		return nil, false, nil
+	}
+	tools, ok := req["tools"].([]any)
+	if !ok || len(tools) == 0 {
+		return nil, false, nil
+	}
+
+	topLevel := make(map[string]bool)
+	for _, raw := range tools {
+		tool, ok := raw.(map[string]any)
+		if !ok {
+			continue
+		}
+		typ := strings.TrimSpace(stringValue(tool["type"]))
+		name := strings.TrimSpace(stringValue(tool["name"]))
+		if (typ == "function" || typ == "custom") && name != "" {
+			topLevel[name] = true
+		}
+	}
+
+	names := make(map[string]ResponsesNamespaceName)
+	for _, raw := range tools {
+		tool, ok := raw.(map[string]any)
+		if !ok || strings.TrimSpace(stringValue(tool["type"])) != "namespace" {
+			continue
+		}
+		namespace := strings.TrimSpace(stringValue(tool["name"]))
+		if namespace == "" || preserved[namespace] {
+			continue
+		}
+		for _, rawChild := range namespaceChildren(tool) {
+			child, ok := rawChild.(map[string]any)
+			if !ok || strings.TrimSpace(stringValue(child["type"])) != "function" {
+				continue
+			}
+			name := strings.TrimSpace(stringValue(child["name"]))
+			if name == "" {
+				continue
+			}
+			flat := flattenNamespaceToolName(namespace, name)
+			entry := ResponsesNamespaceName{Namespace: namespace, Name: name}
+			if topLevel[flat] {
+				return nil, false, fmt.Errorf("namespace tool %q/%q flattens to %q which conflicts with a top-level tool of the same name; this upstream cannot disambiguate them, rename one of the tools", namespace, name, flat)
+			}
+			if prev, exists := names[flat]; exists && prev != entry {
+				return nil, false, fmt.Errorf("namespace tools %q/%q and %q/%q both flatten to %q; this upstream cannot disambiguate them, rename one of the tools", prev.Namespace, prev.Name, namespace, name, flat)
+			}
+			names[flat] = entry
+		}
+	}
+	if len(names) == 0 {
+		return nil, false, nil
+	}
+
+	flattened := make([]any, 0, len(tools)+len(names))
+	seen := make(map[string]bool)
+	for _, raw := range tools {
+		tool, ok := raw.(map[string]any)
+		if !ok || strings.TrimSpace(stringValue(tool["type"])) != "namespace" {
+			flattened = append(flattened, raw)
+			continue
+		}
+		namespace := strings.TrimSpace(stringValue(tool["name"]))
+		if preserved[namespace] {
+			flattened = append(flattened, raw)
+			continue
+		}
+		for _, rawChild := range namespaceChildren(tool) {
+			child, ok := rawChild.(map[string]any)
+			if !ok || strings.TrimSpace(stringValue(child["type"])) != "function" {
+				continue
+			}
+			name := strings.TrimSpace(stringValue(child["name"]))
+			flat := flattenNamespaceToolName(namespace, name)
+			if name == "" || seen[flat] {
+				continue
+			}
+			seen[flat] = true
+			flatChild := make(map[string]any, len(child))
+			for key, value := range child {
+				flatChild[key] = value
+			}
+			flatChild["name"] = flat
+			flattened = append(flattened, flatChild)
+		}
+	}
+	req["tools"] = flattened
+	rewriteNamespaceQualifiedCalls(req["input"], names)
+	if choice, ok := req["tool_choice"].(map[string]any); ok {
+		choiceNamespace := strings.TrimSpace(stringValue(choice["name"]))
+		if strings.TrimSpace(stringValue(choice["type"])) == "namespace" && !preserved[choiceNamespace] {
+			req["tool_choice"] = "auto"
+		} else {
+			rewriteNamespaceQualifiedCall(choice, names)
+		}
+	}
+	return names, true, nil
+}
+
+// RestoreResponsesNamespaceCalls restores flattened function calls in a JSON
+// Responses payload to the namespace/name identity expected by Codex.
+func RestoreResponsesNamespaceCalls(payload []byte, names map[string]ResponsesNamespaceName) ([]byte, bool, error) {
+	if len(payload) == 0 || len(names) == 0 {
+		return payload, false, nil
+	}
+	var value any
+	if err := json.Unmarshal(payload, &value); err != nil {
+		return payload, false, err
+	}
+	changed := restoreResponsesNamespaceValue(value, names)
+	if !changed {
+		return payload, false, nil
+	}
+	var rebuilt bytes.Buffer
+	encoder := json.NewEncoder(&rebuilt)
+	encoder.SetEscapeHTML(false)
+	if err := encoder.Encode(value); err != nil {
+		return payload, false, err
+	}
+	return bytes.TrimSuffix(rebuilt.Bytes(), []byte("\n")), true, nil
+}
+
+func namespaceChildren(tool map[string]any) []any {
+	if children, ok := tool["tools"].([]any); ok && len(children) > 0 {
+		return children
+	}
+	children, _ := tool["children"].([]any)
+	return children
+}
+
+func rewriteNamespaceQualifiedCalls(value any, names map[string]ResponsesNamespaceName) {
+	switch typed := value.(type) {
+	case []any:
+		for _, item := range typed {
+			rewriteNamespaceQualifiedCalls(item, names)
+		}
+	case map[string]any:
+		if strings.TrimSpace(stringValue(typed["type"])) == "function_call" {
+			rewriteNamespaceQualifiedCall(typed, names)
+		}
+		for _, child := range typed {
+			rewriteNamespaceQualifiedCalls(child, names)
+		}
+	}
+}
+
+func rewriteNamespaceQualifiedCall(item map[string]any, names map[string]ResponsesNamespaceName) bool {
+	namespace := strings.TrimSpace(stringValue(item["namespace"]))
+	name := strings.TrimSpace(stringValue(item["name"]))
+	if namespace == "" || name == "" {
+		return false
+	}
+	flat := flattenNamespaceToolName(namespace, name)
+	entry, ok := names[flat]
+	if !ok || entry.Namespace != namespace || entry.Name != name {
+		return false
+	}
+	item["name"] = flat
+	delete(item, "namespace")
+	return true
+}
+
+func restoreResponsesNamespaceValue(value any, names map[string]ResponsesNamespaceName) bool {
+	changed := false
+	switch typed := value.(type) {
+	case []any:
+		for _, item := range typed {
+			changed = restoreResponsesNamespaceValue(item, names) || changed
+		}
+	case map[string]any:
+		if strings.TrimSpace(stringValue(typed["type"])) == "function_call" {
+			if entry, ok := names[strings.TrimSpace(stringValue(typed["name"]))]; ok {
+				typed["name"] = entry.Name
+				typed["namespace"] = entry.Namespace
+				changed = true
+			}
+		}
+		for _, child := range typed {
+			changed = restoreResponsesNamespaceValue(child, names) || changed
+		}
+	}
+	return changed
+}
+
+func stringValue(value any) string {
+	text, _ := value.(string)
+	return text
+}
diff --git a/backend/internal/pkg/apicompat/responses_namespace_test.go b/backend/internal/pkg/apicompat/responses_namespace_test.go
new file mode 100644
index 0000000000..4c8e313c5d
--- /dev/null
+++ b/backend/internal/pkg/apicompat/responses_namespace_test.go
@@ -0,0 +1,164 @@
+package apicompat
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFlattenResponsesNamespaces_RewritesDeclarationHistoryAndChoice(t *testing.T) {
+	req := map[string]any{
+		"model": "gpt-5.5",
+		"tools": []any{
+			map[string]any{"type": "function", "name": "plain", "description": "keep"},
+			map[string]any{
+				"type": "namespace",
+				"name": "collaboration",
+				"tools": []any{
+					map[string]any{"type": "function", "name": "spawn_agent", "description": "spawn", "parameters": map[string]any{"type": "object"}},
+				},
+			},
+		},
+		"tool_choice": map[string]any{"type": "function", "name": "spawn_agent", "namespace": "collaboration"},
+		"input": []any{
+			map[string]any{"type": "function_call", "call_id": "call_1", "name": "spawn_agent", "namespace": "collaboration", "arguments": "{}"},
+			map[string]any{"type": "message", "role": "user", "content": "hi", "name": "spawn_agent", "namespace": "collaboration"},
+		},
+	}
+
+	names, changed, err := FlattenResponsesNamespaces(req)
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Equal(t, ResponsesNamespaceName{Namespace: "collaboration", Name: "spawn_agent"}, names["collaboration__spawn_agent"])
+
+	tools, ok := req["tools"].([]any)
+	require.True(t, ok)
+	require.Len(t, tools, 2)
+	plainTool, ok := tools[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "plain", plainTool["name"])
+	flatTool, ok := tools[1].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "collaboration__spawn_agent", flatTool["name"])
+	require.Equal(t, "spawn", flatTool["description"])
+
+	choice, ok := req["tool_choice"].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "collaboration__spawn_agent", choice["name"])
+	require.NotContains(t, choice, "namespace")
+
+	input, ok := req["input"].([]any)
+	require.True(t, ok)
+	require.Len(t, input, 2)
+	call, ok := input[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "collaboration__spawn_agent", call["name"])
+	require.NotContains(t, call, "namespace")
+	message, ok := input[1].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "spawn_agent", message["name"])
+	require.Equal(t, "collaboration", message["namespace"])
+	require.Equal(t, "gpt-5.5", req["model"])
+}
+
+func TestFlattenResponsesNamespaces_RejectsFlatNameCollision(t *testing.T) {
+	req := map[string]any{"tools": []any{
+		map[string]any{"type": "function", "name": "collaboration__spawn_agent"},
+		map[string]any{"type": "namespace", "name": "collaboration", "tools": []any{
+			map[string]any{"type": "function", "name": "spawn_agent"},
+		}},
+	}}
+
+	_, _, err := FlattenResponsesNamespaces(req)
+	require.ErrorContains(t, err, "conflicts with a top-level tool")
+}
+
+func TestFlattenResponsesNamespaces_NamespaceGroupChoiceFallsBackToAuto(t *testing.T) {
+	req := map[string]any{
+		"tools": []any{map[string]any{
+			"type": "namespace", "name": "collaboration", "tools": []any{
+				map[string]any{"type": "function", "name": "spawn_agent"},
+				map[string]any{"type": "function", "name": "send_message"},
+			},
+		}},
+		"tool_choice": map[string]any{"type": "namespace", "name": "collaboration"},
+	}
+
+	_, changed, err := FlattenResponsesNamespaces(req)
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Equal(t, "auto", req["tool_choice"])
+}
+
+func TestFlattenResponsesNamespacesExcept_PreservesBuiltInNamespaceAndChoice(t *testing.T) {
+	req := map[string]any{
+		"tools": []any{
+			map[string]any{"type": "namespace", "name": "image_gen", "tools": []any{
+				map[string]any{"type": "function", "name": "imagegen"},
+			}},
+			map[string]any{"type": "namespace", "name": "collaboration", "tools": []any{
+				map[string]any{"type": "function", "name": "spawn_agent"},
+			}},
+		},
+		"tool_choice": map[string]any{"type": "namespace", "name": "image_gen"},
+	}
+
+	names, changed, err := FlattenResponsesNamespacesExcept(req, map[string]bool{"image_gen": true})
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Contains(t, names, "collaboration__spawn_agent")
+	tools, ok := req["tools"].([]any)
+	require.True(t, ok)
+	require.Len(t, tools, 2)
+	preservedTool, ok := tools[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "namespace", preservedTool["type"])
+	require.Equal(t, "image_gen", preservedTool["name"])
+	flatTool, ok := tools[1].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "function", flatTool["type"])
+	require.Equal(t, "collaboration__spawn_agent", flatTool["name"])
+	require.Equal(t, map[string]any{"type": "namespace", "name": "image_gen"}, req["tool_choice"])
+}
+
+func TestFlattenResponsesNamespaces_RejectsNamespaceCollision(t *testing.T) {
+	req := map[string]any{"tools": []any{
+		map[string]any{"type": "namespace", "name": "a", "tools": []any{
+			map[string]any{"type": "function", "name": "b__c"},
+		}},
+		map[string]any{"type": "namespace", "name": "a__b", "tools": []any{
+			map[string]any{"type": "function", "name": "c"},
+		}},
+	}}
+
+	_, _, err := FlattenResponsesNamespaces(req)
+	require.ErrorContains(t, err, "both flatten")
+}
+
+func TestRestoreResponsesNamespaceCalls_RewritesOnlyFunctionCalls(t *testing.T) {
+	payload := []byte(`{"type":"response.completed","response":{"output":[{"type":"function_call","name":"collaboration__spawn_agent","call_id":"call_1","arguments":"{}","extra":"keep"},{"type":"function_call","name":"plain","arguments":"{}"},{"type":"message","name":"collaboration__spawn_agent","content":"<tag>&value</tag>"}]}}`)
+	names := map[string]ResponsesNamespaceName{
+		"collaboration__spawn_agent": {Namespace: "collaboration", Name: "spawn_agent"},
+	}
+
+	got, changed, err := RestoreResponsesNamespaceCalls(payload, names)
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.JSONEq(t, `{"type":"response.completed","response":{"output":[{"type":"function_call","name":"spawn_agent","namespace":"collaboration","call_id":"call_1","arguments":"{}","extra":"keep"},{"type":"function_call","name":"plain","arguments":"{}"},{"type":"message","name":"collaboration__spawn_agent","content":"<tag>&value</tag>"}]}}`, string(got))
+	require.Contains(t, string(got), "<tag>&value</tag>")
+	require.NotContains(t, string(got), `\u003c`)
+}
+
+func TestRestoreResponsesNamespaceCalls_RewritesLifecycleItems(t *testing.T) {
+	for _, eventType := range []string{"response.output_item.added", "response.output_item.done"} {
+		t.Run(eventType, func(t *testing.T) {
+			payload := []byte(`{"type":"` + eventType + `","item":{"type":"function_call","name":"collaboration__spawn_agent","arguments":"{}"}}`)
+			got, changed, err := RestoreResponsesNamespaceCalls(payload, map[string]ResponsesNamespaceName{
+				"collaboration__spawn_agent": {Namespace: "collaboration", Name: "spawn_agent"},
+			})
+			require.NoError(t, err)
+			require.True(t, changed)
+			require.JSONEq(t, `{"type":"`+eventType+`","item":{"type":"function_call","name":"spawn_agent","namespace":"collaboration","arguments":"{}"}}`, string(got))
+		})
+	}
+}
diff --git a/backend/internal/service/openai_gateway_forward.go b/backend/internal/service/openai_gateway_forward.go
index b7c850d0c8..6c7d45946a 100644
--- a/backend/internal/service/openai_gateway_forward.go
+++ b/backend/internal/service/openai_gateway_forward.go
@@ -42,6 +42,20 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 	if normalized {
 		body = normalizedBody
 	}
+	wsDecision := s.getOpenAIWSProtocolResolver().Resolve(account)
+	// 仅允许 WS 入站请求走 WS 上游，避免出现 HTTP -> WS 协议混用。
+	wsDecision = resolveOpenAIWSDecisionByClientTransport(wsDecision, GetOpenAIClientTransport(c))
+	passthroughEnabled := account.IsOpenAIPassthroughEnabled()
+	if shouldFlattenOpenAIResponsesNamespaces(account, wsDecision.Transport, passthroughEnabled) {
+		body, err = flattenOpenAIResponsesNamespaces(c, body)
+		if err != nil {
+			setOpsUpstreamError(c, http.StatusBadRequest, err.Error(), "")
+			c.JSON(http.StatusBadRequest, gin.H{"error": gin.H{
+				"type": "invalid_request_error", "message": err.Error(), "param": "tools",
+			}})
+			return nil, err
+		}
+	}
 
 	originalBody := body
 	requestView := newOpenAIRequestView(body)
@@ -64,10 +78,6 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 	if isCodexCLI {
 		codexImageGenerationExplicitToolPolicy = account.CodexImageGenerationExplicitToolPolicy()
 	}
-	wsDecision := s.getOpenAIWSProtocolResolver().Resolve(account)
-	clientTransport := GetOpenAIClientTransport(c)
-	// 仅允许 WS 入站请求走 WS 上游，避免出现 HTTP -> WS 协议混用。
-	wsDecision = resolveOpenAIWSDecisionByClientTransport(wsDecision, clientTransport)
 	if c != nil {
 		c.Set("openai_ws_transport_decision", string(wsDecision.Transport))
 		c.Set("openai_ws_transport_reason", wsDecision.Reason)
@@ -96,7 +106,6 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		}
 		return nil, errors.New("openai ws v1 is temporarily unsupported; use ws v2")
 	}
-	passthroughEnabled := account.IsOpenAIPassthroughEnabled()
 	if passthroughEnabled {
 		if isCodexCLI && codexImageGenerationExplicitToolPolicy == codexImageGenerationExplicitToolPolicyStrip {
 			strippedBody, changed, stripErr := stripOpenAIImageGenerationToolsFromRawPayload(body)
diff --git a/backend/internal/service/openai_gateway_passthrough.go b/backend/internal/service/openai_gateway_passthrough.go
index 8283b54a19..0a19a9d283 100644
--- a/backend/internal/service/openai_gateway_passthrough.go
+++ b/backend/internal/service/openai_gateway_passthrough.go
@@ -919,6 +919,17 @@ func (s *OpenAIGatewayService) handleStreamingResponsePassthrough(
 				trimmedData = strings.TrimSpace(string(normalizedData))
 				line = "data: " + string(normalizedData)
 			}
+			if trimmedData != "[DONE]" {
+				restoredData, restoreErr := restoreOpenAIResponsesNamespacePayload(c, dataBytes)
+				if restoreErr != nil {
+					return resultWithUsage(), fmt.Errorf("restore OpenAI passthrough namespace response: %w", restoreErr)
+				}
+				if !bytes.Equal(restoredData, dataBytes) {
+					dataBytes = restoredData
+					trimmedData = strings.TrimSpace(string(restoredData))
+					line = "data: " + string(restoredData)
+				}
+			}
 			eventType := strings.TrimSpace(gjson.Get(trimmedData, "type").String())
 			if eventType == "response.failed" {
 				failedMessage = extractOpenAISSEErrorMessage(dataBytes)
@@ -1099,6 +1110,10 @@ func (s *OpenAIGatewayService) handleNonStreamingResponsePassthrough(
 	if originalModel != "" && mappedModel != "" && originalModel != mappedModel {
 		body = s.replaceModelInResponseBody(body, mappedModel, originalModel)
 	}
+	body, err = restoreOpenAIResponsesNamespacePayload(c, body)
+	if err != nil {
+		return nil, fmt.Errorf("restore OpenAI passthrough namespace response: %w", err)
+	}
 	if !writeOpenAICompactSSEBridge(c, resp.StatusCode, body) {
 		c.Data(resp.StatusCode, contentType, body)
 	}
@@ -1140,6 +1155,11 @@ func (s *OpenAIGatewayService) handlePassthroughSSEToJSON(resp *http.Response, c
 		}
 		// Correct tool calls in final response
 		body = s.correctToolCallsInResponseBody(body)
+		restoredBody, restoreErr := restoreOpenAIResponsesNamespacePayload(c, body)
+		if restoreErr != nil {
+			return nil, fmt.Errorf("restore OpenAI passthrough namespace response: %w", restoreErr)
+		}
+		body = restoredBody
 	} else {
 		terminalType, terminalPayload, terminalOK := extractOpenAISSETerminalEvent(bodyText)
 		if terminalOK && terminalType == "response.failed" {
diff --git a/backend/internal/service/openai_gateway_response_handling.go b/backend/internal/service/openai_gateway_response_handling.go
index 845428b641..1d70245eb0 100644
--- a/backend/internal/service/openai_gateway_response_handling.go
+++ b/backend/internal/service/openai_gateway_response_handling.go
@@ -310,6 +310,17 @@ func (s *OpenAIGatewayService) handleStreamingResponse(ctx context.Context, resp
 				line = "data: " + data
 				eventType = strings.TrimSpace(gjson.GetBytes(dataBytes, "type").String())
 			}
+			restoredData, restoreErr := restoreOpenAIResponsesNamespacePayload(c, dataBytes)
+			if restoreErr != nil {
+				streamEarlyErr = fmt.Errorf("restore OpenAI namespace response: %w", restoreErr)
+				return
+			}
+			if !bytes.Equal(restoredData, dataBytes) {
+				dataBytes = restoredData
+				data = string(restoredData)
+				line = "data: " + data
+				eventType = strings.TrimSpace(gjson.GetBytes(dataBytes, "type").String())
+			}
 			if sanitizedData, sanitized := sanitizeOpenAIResponseFailedEventForClient(
 				dataBytes,
 				eventType,
@@ -855,7 +866,10 @@ func (s *OpenAIGatewayService) handleNonStreamingResponse(ctx context.Context, r
 	if originalModel != mappedModel {
 		body = s.replaceModelInResponseBody(body, mappedModel, originalModel)
 	}
-
+	body, err = restoreOpenAIResponsesNamespacePayload(c, body)
+	if err != nil {
+		return nil, fmt.Errorf("restore OpenAI namespace response: %w", err)
+	}
 	responseheaders.WriteFilteredHeaders(c.Writer.Header(), resp.Header, s.responseHeaderFilter)
 
 	contentType := "application/json"
@@ -925,6 +939,11 @@ func (s *OpenAIGatewayService) handleSSEToJSON(resp *http.Response, c *gin.Conte
 		}
 		// Correct tool calls in final response
 		body = s.correctToolCallsInResponseBody(body)
+		restoredBody, restoreErr := restoreOpenAIResponsesNamespacePayload(c, body)
+		if restoreErr != nil {
+			return nil, fmt.Errorf("restore OpenAI namespace response: %w", restoreErr)
+		}
+		body = restoredBody
 	} else {
 		terminalType, terminalPayload, terminalOK := extractOpenAISSETerminalEvent(bodyText)
 		if terminalOK && terminalType == "response.failed" {
diff --git a/backend/internal/service/openai_oauth_passthrough_test.go b/backend/internal/service/openai_oauth_passthrough_test.go
index 60790b9e4c..0aa536f94f 100644
--- a/backend/internal/service/openai_oauth_passthrough_test.go
+++ b/backend/internal/service/openai_oauth_passthrough_test.go
@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/apicompat"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/logger"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/openai_compat"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/tlsfingerprint"
@@ -422,6 +423,194 @@ func TestOpenAIGatewayService_OAuthPassthrough_StreamKeepsToolNameAndBodyNormali
 	require.NotContains(t, body, "\"name\":\"edit\"")
 }
 
+func TestOpenAIGatewayService_OAuthPassthrough_NamespaceRequestAndStreamResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(nil))
+	c.Request.Header.Set("User-Agent", "codex_cli_rs/0.144.1")
+
+	originalBody := []byte(`{
+		"model":"gpt-5.5",
+		"stream":true,
+		"instructions":"local-test-instructions",
+		"tools":[
+			{"type":"function","name":"plain","description":"keep","parameters":{"type":"object"}},
+			{"type":"namespace","name":"collaboration","tools":[{"type":"function","name":"spawn_agent","description":"spawn","parameters":{"type":"object"}}]}
+		],
+		"tool_choice":{"type":"function","name":"spawn_agent","namespace":"collaboration"},
+		"input":[{"type":"function_call","call_id":"call_old","name":"spawn_agent","namespace":"collaboration","arguments":"{}"}]
+	}`)
+
+	upstreamSSE := strings.Join([]string{
+		`data: {"type":"response.output_item.added","output_index":0,"item":{"type":"function_call","id":"fc_1","call_id":"call_1","name":"collaboration__spawn_agent","arguments":""}}`,
+		"",
+		`data: {"type":"response.output_item.done","output_index":0,"item":{"type":"function_call","id":"fc_1","call_id":"call_1","name":"collaboration__spawn_agent","arguments":"{}"}}`,
+		"",
+		`data: {"type":"response.completed","response":{"id":"resp_1","status":"completed","output":[{"type":"function_call","id":"fc_1","call_id":"call_1","name":"collaboration__spawn_agent","arguments":"{}"}],"usage":{"input_tokens":2,"output_tokens":1,"total_tokens":3}}}`,
+		"",
+		"data: [DONE]",
+		"",
+	}, "\n")
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}, "x-request-id": []string{"rid_namespace"}},
+		Body:       io.NopCloser(strings.NewReader(upstreamSSE)),
+	}}
+	svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: upstream}
+	account := &Account{
+		ID: 123, Name: "acc", Platform: PlatformOpenAI, Type: AccountTypeOAuth, Concurrency: 1,
+		Credentials: map[string]any{"access_token": "oauth-token", "chatgpt_account_id": "chatgpt-acc"},
+		Extra:       map[string]any{"openai_passthrough": true}, Status: StatusActive, Schedulable: true, RateMultiplier: f64p(1),
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, originalBody)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+
+	require.Len(t, gjson.GetBytes(upstream.lastBody, "tools").Array(), 2)
+	require.Equal(t, "plain", gjson.GetBytes(upstream.lastBody, "tools.0.name").String())
+	require.Equal(t, "function", gjson.GetBytes(upstream.lastBody, "tools.1.type").String())
+	require.Equal(t, "collaboration__spawn_agent", gjson.GetBytes(upstream.lastBody, "tools.1.name").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "tools.1.tools").Exists())
+	require.Equal(t, "collaboration__spawn_agent", gjson.GetBytes(upstream.lastBody, "tool_choice.name").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "tool_choice.namespace").Exists())
+	require.Equal(t, "collaboration__spawn_agent", gjson.GetBytes(upstream.lastBody, "input.0.name").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "input.0.namespace").Exists())
+
+	downstream := rec.Body.String()
+	require.NotContains(t, downstream, "collaboration__spawn_agent")
+	require.Contains(t, downstream, `"name":"spawn_agent"`)
+	require.Contains(t, downstream, `"namespace":"collaboration"`)
+}
+
+func TestOpenAIGatewayService_NativeOAuth_NamespaceRequestAndStreamResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(nil))
+	c.Request.Header.Set("User-Agent", "codex_cli_rs/0.144.1")
+	body := []byte(`{
+		"model":"gpt-5.5","stream":true,"instructions":"test",
+		"tools":[{"type":"namespace","name":"collaboration","tools":[{"type":"function","name":"spawn_agent","parameters":{"type":"object"}}]}],
+		"input":[{"type":"function_call","call_id":"call_old","name":"spawn_agent","namespace":"collaboration","arguments":"{}"}]
+	}`)
+	upstreamSSE := strings.Join([]string{
+		`data: {"type":"response.output_item.added","output_index":0,"item":{"type":"function_call","id":"fc_1","call_id":"call_1","name":"collaboration__spawn_agent","arguments":""}}`,
+		"",
+		`data: {"type":"response.completed","response":{"id":"resp_1","status":"completed","output":[{"type":"function_call","id":"fc_1","call_id":"call_1","name":"collaboration__spawn_agent","arguments":"{}"}],"usage":{"input_tokens":2,"output_tokens":1,"total_tokens":3}}}`,
+		"",
+		"data: [DONE]",
+		"",
+	}, "\n")
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}, "x-request-id": []string{"rid_native_namespace"}},
+		Body:       io.NopCloser(strings.NewReader(upstreamSSE)),
+	}}
+	svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: upstream}
+	account := &Account{
+		ID: 124, Name: "native", Platform: PlatformOpenAI, Type: AccountTypeOAuth, Concurrency: 1,
+		Credentials: map[string]any{"access_token": "oauth-token", "chatgpt_account_id": "chatgpt-acc"},
+		Status:      StatusActive, Schedulable: true, RateMultiplier: f64p(1),
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, "function", gjson.GetBytes(upstream.lastBody, "tools.0.type").String())
+	require.Equal(t, "collaboration__spawn_agent", gjson.GetBytes(upstream.lastBody, "tools.0.name").String())
+	require.Equal(t, "collaboration__spawn_agent", gjson.GetBytes(upstream.lastBody, "input.0.name").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "input.0.namespace").Exists())
+	require.NotContains(t, rec.Body.String(), "collaboration__spawn_agent")
+	require.Contains(t, rec.Body.String(), `"name":"spawn_agent"`)
+	require.Contains(t, rec.Body.String(), `"namespace":"collaboration"`)
+}
+
+func TestOpenAIGatewayService_NativeOAuth_NamespaceNonStreamingResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(nil))
+	setOpenAIResponsesNamespaceNames(c, map[string]apicompat.ResponsesNamespaceName{
+		"collaboration__spawn_agent": {Namespace: "collaboration", Name: "spawn_agent"},
+	})
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"application/json"}},
+		Body: io.NopCloser(strings.NewReader(`{
+			"id":"resp_1","output":[{"type":"function_call","name":"collaboration__spawn_agent","call_id":"call_1","arguments":"{}"}],
+			"usage":{"input_tokens":1,"output_tokens":1,"total_tokens":2}
+		}`)),
+	}
+
+	result, err := (&OpenAIGatewayService{cfg: &config.Config{}}).handleNonStreamingResponse(
+		context.Background(), resp, c, &Account{Type: AccountTypeOAuth}, "gpt-5.5", "gpt-5.5",
+	)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.NotContains(t, rec.Body.String(), "collaboration__spawn_agent")
+	require.Contains(t, rec.Body.String(), `"name":"spawn_agent"`)
+	require.Contains(t, rec.Body.String(), `"namespace":"collaboration"`)
+}
+
+func TestOpenAIGatewayService_OAuthPassthrough_NamespaceNonStreamingResponse(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(nil))
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"application/json"}},
+		Body:       io.NopCloser(strings.NewReader(`{"id":"resp_1","output":[{"type":"function_call","name":"collaboration__spawn_agent","call_id":"call_1","arguments":"{}"}],"usage":{"input_tokens":1,"output_tokens":1}}`)),
+	}
+	names := map[string]apicompat.ResponsesNamespaceName{
+		"collaboration__spawn_agent": {Namespace: "collaboration", Name: "spawn_agent"},
+	}
+	setOpenAIResponsesNamespaceNames(c, names)
+
+	result, err := (&OpenAIGatewayService{cfg: &config.Config{}}).handleNonStreamingResponsePassthrough(
+		context.Background(), resp, c, "gpt-5.5", "",
+	)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.NotContains(t, rec.Body.String(), "collaboration__spawn_agent")
+	require.Contains(t, rec.Body.String(), `"name":"spawn_agent"`)
+	require.Contains(t, rec.Body.String(), `"namespace":"collaboration"`)
+}
+
+func TestOpenAIGatewayService_OAuthPassthrough_NamespaceCollisionReturnsBadRequest(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(nil))
+	c.Request.Header.Set("User-Agent", "codex_cli_rs/0.144.1")
+	body := []byte(`{
+		"model":"gpt-5.5","stream":true,"instructions":"test",
+		"tools":[
+			{"type":"function","name":"collaboration__spawn_agent","parameters":{"type":"object"}},
+			{"type":"namespace","name":"collaboration","tools":[{"type":"function","name":"spawn_agent","parameters":{"type":"object"}}]}
+		],"input":"hi"
+	}`)
+	upstream := &httpUpstreamRecorder{}
+	svc := &OpenAIGatewayService{cfg: &config.Config{}, httpUpstream: upstream}
+	account := &Account{
+		ID: 123, Name: "acc", Platform: PlatformOpenAI, Type: AccountTypeOAuth, Concurrency: 1,
+		Credentials: map[string]any{"access_token": "oauth-token", "chatgpt_account_id": "chatgpt-acc"},
+		Extra:       map[string]any{"openai_passthrough": true}, Status: StatusActive, Schedulable: true, RateMultiplier: f64p(1),
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.Error(t, err)
+	require.Nil(t, result)
+	require.Nil(t, upstream.lastReq)
+	require.Equal(t, http.StatusBadRequest, rec.Code)
+	require.Equal(t, "invalid_request_error", gjson.Get(rec.Body.String(), "error.type").String())
+	require.Equal(t, "tools", gjson.Get(rec.Body.String(), "error.param").String())
+	require.Contains(t, gjson.Get(rec.Body.String(), "error.message").String(), "conflicts with a top-level tool")
+}
+
 func TestOpenAIGatewayService_OAuthPassthrough_CompactUsesJSONAndKeepsNonStreaming(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 
diff --git a/backend/internal/service/openai_responses_namespace.go b/backend/internal/service/openai_responses_namespace.go
new file mode 100644
index 0000000000..7d71b64814
--- /dev/null
+++ b/backend/internal/service/openai_responses_namespace.go
@@ -0,0 +1,83 @@
+package service
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/apicompat"
+	"github.com/gin-gonic/gin"
+)
+
+const openAIResponsesNamespaceNamesContextKey = "openai_responses_namespace_names"
+
+// shouldFlattenOpenAIResponsesNamespaces 判定原生 Responses 转发前是否摊平
+// Codex namespace 工具。WSv2 上游原生支持 namespace，且 WS 出口
+// （openai_ws_forwarder_v2）原样转发上游事件、不经 HTTP 回程还原，摊平后的
+// 平名无法还原会破坏客户端工具匹配，因此实际走 WSv2 分支的请求保持 namespace
+// 原样。透传账号先于 WSv2 分支经 HTTP 转发返回，仍需摊平。
+func shouldFlattenOpenAIResponsesNamespaces(account *Account, transport OpenAIUpstreamTransport, passthroughEnabled bool) bool {
+	if account == nil || account.Type != AccountTypeOAuth {
+		return false
+	}
+	if transport == OpenAIUpstreamTransportResponsesWebsocketV2 && !passthroughEnabled {
+		return false
+	}
+	return true
+}
+
+func flattenOpenAIResponsesNamespaces(c *gin.Context, body []byte) ([]byte, error) {
+	if !bytes.Contains(body, []byte(`"namespace"`)) {
+		return body, nil
+	}
+	var requestBody map[string]any
+	if err := json.Unmarshal(body, &requestBody); err != nil {
+		return body, fmt.Errorf("decode OpenAI namespace body: %w", err)
+	}
+	names, changed, err := apicompat.FlattenResponsesNamespacesExcept(requestBody, map[string]bool{"image_gen": true})
+	if err != nil {
+		return body, err
+	}
+	if !changed {
+		return body, nil
+	}
+	rebuilt, err := marshalOpenAIUpstreamJSON(requestBody)
+	if err != nil {
+		return body, fmt.Errorf("encode OpenAI namespace body: %w", err)
+	}
+	setOpenAIResponsesNamespaceNames(c, names)
+	return rebuilt, nil
+}
+
+func setOpenAIResponsesNamespaceNames(c *gin.Context, names map[string]apicompat.ResponsesNamespaceName) {
+	if c != nil && len(names) > 0 {
+		c.Set(openAIResponsesNamespaceNamesContextKey, names)
+	}
+}
+
+func openAIResponsesNamespaceNames(c *gin.Context) map[string]apicompat.ResponsesNamespaceName {
+	if c == nil {
+		return nil
+	}
+	value, ok := c.Get(openAIResponsesNamespaceNamesContextKey)
+	if !ok {
+		return nil
+	}
+	names, _ := value.(map[string]apicompat.ResponsesNamespaceName)
+	return names
+}
+
+func restoreOpenAIResponsesNamespacePayload(c *gin.Context, payload []byte) ([]byte, error) {
+	names := openAIResponsesNamespaceNames(c)
+	if len(names) == 0 || !json.Valid(payload) {
+		return payload, nil
+	}
+	restored, changed, err := apicompat.RestoreResponsesNamespaceCalls(payload, names)
+	if err != nil {
+		return payload, err
+	}
+	if changed {
+		return restored, nil
+	}
+	return payload, nil
+}
diff --git a/backend/internal/service/openai_responses_namespace_test.go b/backend/internal/service/openai_responses_namespace_test.go
new file mode 100644
index 0000000000..7aa1392260
--- /dev/null
+++ b/backend/internal/service/openai_responses_namespace_test.go
@@ -0,0 +1,34 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestShouldFlattenOpenAIResponsesNamespaces(t *testing.T) {
+	oauth := &Account{Type: AccountTypeOAuth}
+	apiKey := &Account{Type: AccountTypeAPIKey}
+
+	tests := []struct {
+		name               string
+		account            *Account
+		transport          OpenAIUpstreamTransport
+		passthroughEnabled bool
+		want               bool
+	}{
+		{name: "oauth_http", account: oauth, transport: OpenAIUpstreamTransportHTTPSSE, want: true},
+		{name: "oauth_http_passthrough", account: oauth, transport: OpenAIUpstreamTransportHTTPSSE, passthroughEnabled: true, want: true},
+		// WSv2 出口原样转发上游事件、不做回程还原，摊平会让客户端收到无法匹配的平名。
+		{name: "oauth_wsv2", account: oauth, transport: OpenAIUpstreamTransportResponsesWebsocketV2, want: false},
+		// 透传账号先于 WSv2 分支经 HTTP 转发返回，仍需摊平。
+		{name: "oauth_wsv2_passthrough", account: oauth, transport: OpenAIUpstreamTransportResponsesWebsocketV2, passthroughEnabled: true, want: true},
+		{name: "apikey_http", account: apiKey, transport: OpenAIUpstreamTransportHTTPSSE, want: false},
+		{name: "nil_account", account: nil, transport: OpenAIUpstreamTransportHTTPSSE, want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, shouldFlattenOpenAIResponsesNamespaces(tt.account, tt.transport, tt.passthroughEnabled))
+		})
+	}
+}