fix(config): allow duplicate model_name for load balancing

Remove duplicate model_name check in ValidateModelList to support
load balancing feature where multiple configs can share the same
model_name for round-robin selection.

Update tests to reflect the new behavior.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/config/config.go

@@ -583,20 +583,13 @@ func (c *Config) HasProvidersConfig() bool {
 }
 
 // ValidateModelList validates all ModelConfig entries in the model_list.
-// It checks that each model_name/model combination is valid and that
-// model_name is unique across all entries.
+// It checks that each model config is valid.
+// Note: Multiple entries with the same model_name are allowed for load balancing.
 func (c *Config) ValidateModelList() error {
-	seen := make(map[string]int)
 	for i := range c.ModelList {
 		if err := c.ModelList[i].Validate(); err != nil {
 			return fmt.Errorf("model_list[%d]: %w", i, err)
 		}
-		// Check for duplicate model_name
-		name := c.ModelList[i].ModelName
-		if prevIdx, exists := seen[name]; exists {
-			return fmt.Errorf("model_list: duplicate model_name %q at index %d and %d", name, prevIdx, i)
-		}
-		seen[name] = i
 	}
 	return nil
 }

pkg/config/model_config_test.go

@@ -195,18 +195,19 @@ func TestConfig_ValidateModelList(t *testing.T) {
 			wantErr: false,
 		},
 		{
-			name: "duplicate model_name",
+			// Load balancing: multiple entries with same model_name are allowed
+			name: "duplicate model_name for load balancing",
 			config: &Config{
 				ModelList: []ModelConfig{
 					{ModelName: "gpt-4", Model: "openai/gpt-4o", APIKey: "key1"},
 					{ModelName: "gpt-4", Model: "openai/gpt-4-turbo", APIKey: "key2"},
 				},
 			},
-			wantErr: true,
-			errMsg:  "duplicate model_name",
+			wantErr: false, // Changed: duplicates are allowed for load balancing
 		},
 		{
-			name: "duplicate model_name non-adjacent",
+			// Load balancing: non-adjacent entries with same model_name are also allowed
+			name: "duplicate model_name non-adjacent for load balancing",
 			config: &Config{
 				ModelList: []ModelConfig{
 					{ModelName: "model-a", Model: "openai/gpt-4o"},
@@ -214,8 +215,7 @@ func TestConfig_ValidateModelList(t *testing.T) {
 					{ModelName: "model-a", Model: "openai/gpt-4-turbo"},
 				},
 			},
-			wantErr: true,
-			errMsg:  "duplicate model_name \"model-a\"",
+			wantErr: false, // Changed: duplicates are allowed for load balancing
 		},
 	}