fix(go-models): add VolcEngine model listing suffix (#15234)

## Summary
- add the VolcEngine `models` URL suffix used by the existing Go
`ListModels` implementation
- return a clear error when the VolcEngine models suffix is missing
- add focused VolcEngine model-listing regression tests

## What changed
- Added `url_suffix.models` to `conf/models/volcengine.json`.
- Normalized the configured models suffix before building the request
URL.
- Covered config loading, successful model listing, upstream errors, and
missing suffix handling.

## Why
`VolcEngine.ListModels` already builds requests from `URLSuffix.Models`,
but the bundled VolcEngine config did not define that suffix. That left
the model-listing path unable to call the documented `/models` endpoint
from the existing provider config.

Fixes #14701

Co-authored-by: Jin Hai <haijin.chn@gmail.com>

conf/models/volcengine.json

@@ -6,7 +6,8 @@
   "url_suffix": {
     "chat": "chat/completions",
     "files": "files",
-    "embedding": "embeddings/multimodal"
+    "embedding": "embeddings/multimodal",
+    "models": "models"
   },
   "class": "volcengine",
   "models": [
@@ -29,4 +30,4 @@
       ]
     }
   ]
-}
+}

internal/entity/models/volcengine.go

@@ -551,8 +551,12 @@ func (z *VolcEngine) ListModels(apiConfig *APIConfig) ([]string, error) {
 	if baseURL == "" {
 		return nil, fmt.Errorf("volcengine: no base URL configured for region %q", region)
 	}
+	modelsSuffix := strings.Trim(strings.TrimSpace(z.URLSuffix.Models), "/")
+	if modelsSuffix == "" {
+		return nil, fmt.Errorf("volcengine: models URL suffix is not configured")
+	}
 
-	url := fmt.Sprintf("%s/%s", strings.TrimSuffix(baseURL, "/"), z.URLSuffix.Models)
+	url := fmt.Sprintf("%s/%s", strings.TrimSuffix(baseURL, "/"), modelsSuffix)
 
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {

internal/entity/models/volcengine_test.go

@@ -0,0 +1,110 @@
+package models
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func newVolcEngineServer(t *testing.T, handler func(t *testing.T, r *http.Request, w http.ResponseWriter)) *httptest.Server {
+	t.Helper()
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		handler(t, r, w)
+	}))
+}
+
+func newVolcEngineForTest(baseURL string) *VolcEngine {
+	return NewVolcEngine(
+		map[string]string{"default": baseURL},
+		URLSuffix{
+			Chat:      "chat/completions",
+			Files:     "files",
+			Embedding: "embeddings/multimodal",
+			Models:    "/models",
+		},
+	)
+}
+
+func TestVolcEngineConfigDeclaresModelsSuffix(t *testing.T) {
+	var provider struct {
+		URLSuffix URLSuffix `json:"url_suffix"`
+	}
+
+	for _, candidate := range []string{
+		filepath.Join("..", "..", "..", "conf", "models", "volcengine.json"),
+		filepath.Join("conf", "models", "volcengine.json"),
+	} {
+		data, err := os.ReadFile(candidate)
+		if err != nil {
+			continue
+		}
+		if err := json.Unmarshal(data, &provider); err != nil {
+			t.Fatalf("unmarshal %s: %v", candidate, err)
+		}
+		if provider.URLSuffix.Models != "models" {
+			t.Fatalf("models suffix=%q, want models", provider.URLSuffix.Models)
+		}
+		return
+	}
+
+	t.Fatal("could not locate conf/models/volcengine.json")
+}
+
+func TestVolcEngineListModelsHappyPath(t *testing.T) {
+	srv := newVolcEngineServer(t, func(t *testing.T, r *http.Request, w http.ResponseWriter) {
+		if r.Method != http.MethodGet {
+			t.Errorf("method=%s", r.Method)
+		}
+		if r.URL.Path != "/models" {
+			t.Errorf("path=%s", r.URL.Path)
+		}
+		if got := r.Header.Get("Authorization"); got != "Bearer test-key" {
+			t.Errorf("Authorization=%q", got)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{
+			"object": "list",
+			"data": [
+				{"id": "doubao-seed-2-0-pro-260215", "owned_by": "volcengine"},
+				{"id": "doubao-embedding-vision-251215"}
+			]
+		}`))
+	})
+	defer srv.Close()
+
+	apiKey := "test-key"
+	models, err := newVolcEngineForTest(srv.URL).ListModels(&APIConfig{ApiKey: &apiKey})
+	if err != nil {
+		t.Fatalf("ListModels: %v", err)
+	}
+	if strings.Join(models, ",") != "doubao-seed-2-0-pro-260215@volcengine,doubao-embedding-vision-251215" {
+		t.Errorf("models=%v", models)
+	}
+}
+
+func TestVolcEngineListModelsRejectsProviderError(t *testing.T) {
+	srv := newVolcEngineServer(t, func(t *testing.T, r *http.Request, w http.ResponseWriter) {
+		http.Error(w, "bad key", http.StatusUnauthorized)
+	})
+	defer srv.Close()
+
+	apiKey := "test-key"
+	_, err := newVolcEngineForTest(srv.URL).ListModels(&APIConfig{ApiKey: &apiKey})
+	if err == nil || !strings.Contains(err.Error(), "401 Unauthorized") || !strings.Contains(err.Error(), "bad key") {
+		t.Fatalf("expected provider error with status and body, got %v", err)
+	}
+}
+
+func TestVolcEngineListModelsRequiresModelsSuffix(t *testing.T) {
+	apiKey := "test-key"
+	model := NewVolcEngine(map[string]string{"default": "http://unused"}, URLSuffix{})
+
+	_, err := model.ListModels(&APIConfig{ApiKey: &apiKey})
+	if err == nil || !strings.Contains(err.Error(), "models URL suffix is not configured") {
+		t.Fatalf("expected missing models suffix error, got %v", err)
+	}
+}