feat: implement advanced condition-based heuristic model routing

Upgrades the routing engine to support tag, token limit, multimodal, reasoning, and tool calling conditions. Adds unit tests for the new routing features.

internal/providers/helpers.go

@@ -10,6 +10,22 @@ import (
 	"gophergate/internal/models"
 )
 
+func sanitizeFunctionName(name string) string {
+	var sb strings.Builder
+	for _, ch := range name {
+		if (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_' || ch == '-' {
+			sb.WriteRune(ch)
+		} else {
+			sb.WriteRune('_')
+		}
+	}
+	res := sb.String()
+	if res == "" {
+		return "function"
+	}
+	return res
+}
+
 // MessagesToOpenAIJSON converts unified messages to OpenAI-compatible JSON, including tools and images.
 func MessagesToOpenAIJSON(messages []models.UnifiedMessage) ([]interface{}, error) {
 	var result []interface{}
@@ -35,7 +51,7 @@ func MessagesToOpenAIJSON(messages []models.UnifiedMessage) ([]interface{}, erro
 			msg["tool_call_id"] = id
 
 			if m.Name != nil {
-				msg["name"] = *m.Name
+				msg["name"] = sanitizeFunctionName(*m.Name)
 			}
 			result = append(result, msg)
 			continue
@@ -91,6 +107,7 @@ func MessagesToOpenAIJSON(messages []models.UnifiedMessage) ([]interface{}, erro
 				if sanitizedCalls[i].Type == "" {
 					sanitizedCalls[i].Type = "function"
 				}
+				sanitizedCalls[i].Function.Name = sanitizeFunctionName(sanitizedCalls[i].Function.Name)
 			}
 			msg["tool_calls"] = sanitizedCalls
 			msg["content"] = "" // OpenAI requirement: content must be string if tool_calls present
@@ -124,11 +141,25 @@ func BuildOpenAIBody(request *models.UnifiedRequest, messagesJSON []interface{},
 		body["max_tokens"] = *request.MaxTokens
 	}
 	if len(request.Tools) > 0 {
-		body["tools"] = request.Tools
+		sanitizedTools := make([]models.Tool, len(request.Tools))
+		copy(sanitizedTools, request.Tools)
+		for i := range sanitizedTools {
+			if sanitizedTools[i].Type == "function" {
+				sanitizedTools[i].Function.Name = sanitizeFunctionName(sanitizedTools[i].Function.Name)
+			}
+		}
+		body["tools"] = sanitizedTools
 	}
 	if request.ToolChoice != nil {
 		var toolChoice interface{}
 		if err := json.Unmarshal(request.ToolChoice, &toolChoice); err == nil {
+			if tcMap, ok := toolChoice.(map[string]interface{}); ok {
+				if funcMap, ok := tcMap["function"].(map[string]interface{}); ok {
+					if name, ok := funcMap["name"].(string); ok {
+						funcMap["name"] = sanitizeFunctionName(name)
+					}
+				}
+			}
 			body["tool_choice"] = toolChoice
 		}
 	}