fix(opencode): correct Zen qwen3.8-max endpoint and reject unsupported models

- Route qwen3.8-max to Chat Completions on OpenCode Zen mode instead of Messages
- Fast-reject unsupported model families (gemini-*, jev-*) with HTTP 400 on OpenCode gateway to avoid upstream 404 failovers and strike accumulation
- Sync frontend DEFAULT_OPENCODE_ZEN_PROTOCOL_RULES with backend

backend/internal/service/account_test_service.go

@@ -436,6 +436,9 @@ func (s *AccountTestService) testOpenCodeGoAccountConnection(c *gin.Context, acc
 		testModelID = DefaultOpenCodeGoTestModel
 	}
 	testModelID = account.GetMappedModel(testModelID)
+	if IsOpenCodeUnsupportedModel(testModelID) {
+		return fmt.Errorf("model %q is not supported on OpenCode standard gateway (gemini models require Google SDK endpoint, jev models require System One endpoint)", testModelID)
+	}
 	proto := account.GetAPIProtocol()
 	switch proto {
 	case APIProtocolChatCompletions, APIProtocolAnthropic, APIProtocolResponses:

backend/internal/service/openai_gateway_chat_completions.go

@@ -118,6 +118,9 @@ func (s *OpenAIGatewayService) forwardAsChatCompletions(
 	// 规则未命中一律兜底 Chat Completions，只有显式 Responses 才走下方转换链。
 	if account.IsOpenCodeGo() {
 		mapped := resolveOpenCodeGoMappedModel(account, body, defaultMappedModel)
+		if IsOpenCodeUnsupportedModel(mapped) {
+			return nil, writeOpenCodeUnsupportedModelError(c, false, mapped)
+		}
 		proto := openCodeGoNativeProtocol(account, mapped)
 		if proto != APIProtocolResponses {
 			if isResponsesShape {

backend/internal/service/openai_gateway_forward.go

@@ -161,6 +161,9 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 
 	if account.IsOpenCodeGo() {
 		mapped := resolveOpenCodeGoMappedModel(account, body, "")
+		if IsOpenCodeUnsupportedModel(mapped) {
+			return nil, writeOpenCodeUnsupportedModelError(c, false, mapped)
+		}
 		switch openCodeGoNativeProtocol(account, mapped) {
 		case APIProtocolAnthropic:
 			return s.forwardResponsesViaNativeAnthropic(ctx, c, account, body, "")

backend/internal/service/openai_gateway_messages.go

@@ -56,6 +56,9 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 	// OpenCode Go：按模型原生协议分流。规则未命中兜底 Chat Completions。
 	if account.IsOpenCodeGo() {
 		mapped := resolveOpenCodeGoMappedModel(account, body, defaultMappedModel)
+		if IsOpenCodeUnsupportedModel(mapped) {
+			return nil, writeOpenCodeUnsupportedModelError(c, true, mapped)
+		}
 		switch openCodeGoNativeProtocol(account, mapped) {
 		case APIProtocolAnthropic:
 			return s.forwardAnthropicViaNativeAnthropicEndpoint(ctx, c, account, body, defaultMappedModel)

backend/internal/service/opencode_go.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
+	"github.com/gin-gonic/gin"
 )
 
 // OpenCode Go 是 OpenCode Zen 的订阅网关：同一 API Key 下按模型分流到
@@ -67,6 +68,39 @@ func normalizeOpenCodeGoModelID(model string) string {
 	return model
 }
 
+// IsOpenCodeUnsupportedModel 判断请求的模型是否属于 OpenCode 专有协议端点模型。
+// 官方 Zen 上 gemini-* 仅走 Google SDK 专属端点 /zen/v1/models/<id>，
+// jev-* 仅走 SystemOne 专属端点 /zen/v1/systemone，
+// 在通用 Chat Completions / Anthropic Messages / Responses 网关端点上不可用。
+func IsOpenCodeUnsupportedModel(model string) bool {
+	normalized := normalizeOpenCodeGoModelID(model)
+	return strings.HasPrefix(normalized, "gemini-") || strings.HasPrefix(normalized, "jev-")
+}
+
+func writeOpenCodeUnsupportedModelError(c *gin.Context, isAnthropic bool, model string) error {
+	msg := fmt.Sprintf("Model '%s' is not supported on OpenCode standard gateway (gemini models require Google SDK endpoint, jev models require System One endpoint)", model)
+	if c != nil {
+		if isAnthropic {
+			c.JSON(http.StatusBadRequest, gin.H{
+				"type": "error",
+				"error": gin.H{
+					"type":    "invalid_request_error",
+					"message": msg,
+				},
+			})
+		} else {
+			c.JSON(http.StatusBadRequest, gin.H{
+				"error": gin.H{
+					"type":    "invalid_request_error",
+					"code":    "model_not_supported",
+					"message": msg,
+				},
+			})
+		}
+	}
+	return fmt.Errorf("opencode unsupported model: %s", model)
+}
+
 // OpenCodeGoProtocolRule is one model-pattern → native protocol mapping.
 // Pattern is an exact ID or a suffix glob (foo* / *). First match wins.
 type OpenCodeGoProtocolRule struct {
@@ -86,13 +120,15 @@ func DefaultOpenCodeGoProtocolRules() []OpenCodeGoProtocolRule {
 }
 
 // DefaultOpenCodeZenProtocolRules 对齐 https://opencode.ai/docs/zen/ 端点表：
-// GPT/Grok/Muse Spark → Responses，Claude/Qwen → Anthropic，其余 Chat Completions。
+// GPT/Grok/Muse Spark → Responses，Claude/Qwen(除 qwen3.8-max) → Anthropic，
+// qwen3.8-max 及其余模型 → Chat Completions。
 func DefaultOpenCodeZenProtocolRules() []OpenCodeGoProtocolRule {
 	return []OpenCodeGoProtocolRule{
 		{Pattern: "grok-*", Protocol: APIProtocolResponses},
 		{Pattern: "gpt-*", Protocol: APIProtocolResponses},
 		{Pattern: "muse-spark-*", Protocol: APIProtocolResponses},
 		{Pattern: "claude-*", Protocol: APIProtocolAnthropic},
+		{Pattern: "qwen3.8-max", Protocol: APIProtocolChatCompletions},
 		{Pattern: "qwen*", Protocol: APIProtocolAnthropic},
 	}
 }

backend/internal/service/opencode_go_test.go

@@ -50,8 +50,14 @@ func TestResolveOpenCodeGoUpstreamProtocol(t *testing.T) {
 	zen := &Account{Platform: PlatformOpenCodeGo, Credentials: map[string]any{"account_mode": AccountModeZen, "api_protocol": APIProtocolAdaptive}}
 	require.Equal(t, APIProtocolChatCompletions, zen.ResolveOpenCodeGoUpstreamProtocol("minimax-m3"))
 	require.Equal(t, APIProtocolAnthropic, zen.ResolveOpenCodeGoUpstreamProtocol("claude-opus-4-6"))
+	require.Equal(t, APIProtocolChatCompletions, zen.ResolveOpenCodeGoUpstreamProtocol("qwen3.8-max"))
+	require.Equal(t, APIProtocolAnthropic, zen.ResolveOpenCodeGoUpstreamProtocol("qwen3.8-flash"))
+	require.Equal(t, APIProtocolAnthropic, zen.ResolveOpenCodeGoUpstreamProtocol("qwen3.7-max"))
 	require.Equal(t, DefaultOpenCodeZenBaseURL, zen.GetOpenAIBaseURL())
 
+	goAccount := &Account{Platform: PlatformOpenCodeGo, Credentials: map[string]any{"account_mode": AccountModeGo, "api_protocol": APIProtocolAdaptive}}
+	require.Equal(t, APIProtocolAnthropic, goAccount.ResolveOpenCodeGoUpstreamProtocol("qwen3.8-max"))
+
 	require.Equal(t, "", (&Account{Platform: PlatformKimi}).ResolveOpenCodeGoUpstreamProtocol("glm-5.3"))
 }
 
@@ -235,3 +241,29 @@ func TestDefaultOpenCodeGoModelIDsCoverDocumentedCatalog(t *testing.T) {
 	require.Contains(t, ids, "glm-5.3")
 	require.NotEmpty(t, ids)
 }
+
+func TestIsOpenCodeUnsupportedModel(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		model string
+		want  bool
+	}{
+		{"gemini-3.8-flash", true},
+		{"gemini-3.7-flash", true},
+		{"opencode/gemini-3.8-flash", true},
+		{"opencode-go/gemini-3.1-pro", true},
+		{"jev-1.13", true},
+		{"jev-1.13-free", true},
+		{"opencode/jev-1.13", true},
+		{"qwen3.8-max", false},
+		{"qwen3.8-flash", false},
+		{"gpt-5.6-luna", false},
+		{"grok-4.6", false},
+		{"minimax-m3", false},
+		{"glm-5.3", false},
+		{"", false},
+	}
+	for _, tc := range cases {
+		require.Equal(t, tc.want, IsOpenCodeUnsupportedModel(tc.model), "model=%s", tc.model)
+	}
+}

backend/internal/service/opencode_unsupported_models_test.go

@@ -0,0 +1,138 @@
+package service
+
+import (
+	"bytes"
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestForwardOpenCodeUnsupportedModels_ChatCompletionsReturns400(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	account := &Account{
+		ID:       101,
+		Platform: PlatformOpenCodeGo,
+		Type:     AccountTypeAPIKey,
+		Credentials: map[string]any{
+			"api_key":      "test-key",
+			"account_mode": AccountModeZen,
+		},
+	}
+
+	svc := &OpenAIGatewayService{
+		cfg: &config.Config{},
+	}
+
+	for _, model := range []string{"gemini-3.8-flash", "jev-1.13", "opencode/gemini-3.7-flash", "opencode-go/jev-1.13-free"} {
+		rec := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(rec)
+		body := []byte(`{"model":"` + model + `","messages":[{"role":"user","content":"hello"}]}`)
+		c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", bytes.NewReader(body))
+
+		result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+		require.Nil(t, result)
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "opencode unsupported model")
+
+		require.Equal(t, http.StatusBadRequest, rec.Code)
+		respBody := rec.Body.String()
+		require.Equal(t, "invalid_request_error", gjson.Get(respBody, "error.type").String())
+		require.Equal(t, "model_not_supported", gjson.Get(respBody, "error.code").String())
+		require.Contains(t, gjson.Get(respBody, "error.message").String(), "not supported on OpenCode standard gateway")
+	}
+}
+
+func TestForwardOpenCodeUnsupportedModels_ResponsesReturns400(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	account := &Account{
+		ID:       102,
+		Platform: PlatformOpenCodeGo,
+		Type:     AccountTypeAPIKey,
+		Credentials: map[string]any{
+			"api_key":      "test-key",
+			"account_mode": AccountModeZen,
+		},
+	}
+
+	svc := &OpenAIGatewayService{
+		cfg: &config.Config{},
+	}
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	body := []byte(`{"model":"gemini-3.8-flash","input":[{"role":"user","content":"hello"}]}`)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/responses", bytes.NewReader(body))
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.Nil(t, result)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "opencode unsupported model")
+
+	require.Equal(t, http.StatusBadRequest, rec.Code)
+	respBody := rec.Body.String()
+	require.Equal(t, "invalid_request_error", gjson.Get(respBody, "error.type").String())
+	require.Equal(t, "model_not_supported", gjson.Get(respBody, "error.code").String())
+}
+
+func TestForwardOpenCodeUnsupportedModels_MessagesReturns400(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	account := &Account{
+		ID:       103,
+		Platform: PlatformOpenCodeGo,
+		Type:     AccountTypeAPIKey,
+		Credentials: map[string]any{
+			"api_key":      "test-key",
+			"account_mode": AccountModeZen,
+		},
+	}
+
+	svc := &OpenAIGatewayService{
+		cfg: &config.Config{},
+	}
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	body := []byte(`{"model":"gemini-3.8-flash","messages":[{"role":"user","content":"hello"}]}`)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+
+	result, err := svc.ForwardAsAnthropic(context.Background(), c, account, body, "", "")
+	require.Nil(t, result)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "opencode unsupported model")
+
+	require.Equal(t, http.StatusBadRequest, rec.Code)
+	respBody := rec.Body.String()
+	require.Equal(t, "invalid_request_error", gjson.Get(respBody, "error.type").String())
+	require.Contains(t, gjson.Get(respBody, "error.message").String(), "not supported on OpenCode standard gateway")
+}
+
+func TestAccountTestService_OpenCodeUnsupportedModelReturnsError(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	c.Request = httptest.NewRequest(http.MethodPost, "/test", nil)
+
+	account := &Account{
+		ID:       104,
+		Platform: PlatformOpenCodeGo,
+		Type:     AccountTypeAPIKey,
+	}
+
+	svc := &AccountTestService{}
+	err := svc.testOpenCodeGoAccountConnection(c, account, "gemini-3.8-flash", "hi")
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "not supported on OpenCode standard gateway")
+
+	err = svc.testOpenCodeGoAccountConnection(c, account, "jev-1.13", "hi")
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "not supported on OpenCode standard gateway")
+}

frontend/src/components/account/credentialsBuilder.ts

@@ -304,6 +304,7 @@ export const DEFAULT_OPENCODE_ZEN_PROTOCOL_RULES: OpenCodeGoProtocolRule[] = [
   { pattern: 'gpt-*', protocol: 'responses' },
   { pattern: 'muse-spark-*', protocol: 'responses' },
   { pattern: 'claude-*', protocol: 'anthropic' },
+  { pattern: 'qwen3.8-max', protocol: 'chat_completions' },
   { pattern: 'qwen*', protocol: 'anthropic' }
 ]