fix(gemini): group adjacent tool messages and ensure correct role sequence

- Group consecutive 'tool' messages into a single Gemini content message with multiple 'functionResponse' parts
- Ensure assistant tool calls are properly mapped and sent
- Maintain v1beta for preview and newer models
- Added debug logging for API errors

internal/providers/gemini.go

@@ -77,36 +77,38 @@ type GeminiFunctionResponse struct {
 func (p *GeminiProvider) ChatCompletion(ctx context.Context, req *models.UnifiedRequest) (*models.ChatCompletionResponse, error) {
 	// Gemini mapping
 	var contents []GeminiContent
-	for _, msg := range req.Messages {
+	
+	// Group tool messages together for Gemini
+	for i := 0; i < len(req.Messages); i++ {
+		msg := req.Messages[i]
 		role := "user"
 		if msg.Role == "assistant" {
 			role = "model"
 		} else if msg.Role == "tool" {
-			role = "function" // Function results use 'function' role in Gemini contents
+			role = "function"
 		}
 		
 		var parts []GeminiPart
 		
-		// Handle tool responses
 		if msg.Role == "tool" {
+			// Check if we can group this with previous tool message
+			// Actually, it's easier to just collect all current and subsequent tool messages
+			for j := i; j < len(req.Messages) && req.Messages[j].Role == "tool"; j++ {
+				m := req.Messages[j]
 				text := ""
-			if len(msg.Content) > 0 {
+				if len(m.Content) > 0 {
-				text = msg.Content[0].Text
+					text = m.Content[0].Text
 				}
 				
-			// Gemini expects functionResponse to be an object
 				name := "unknown_function"
-			if msg.Name != nil {
+				if m.Name != nil {
-				name = *msg.Name
+					name = *m.Name
 				}
 				
-			// Try to parse text as JSON if it looks like it, Gemini expects an object
 				var responseObj interface{}
 				if err := json.Unmarshal([]byte(text), &responseObj); err != nil {
-				// If not valid JSON, wrap it in an object
 					responseObj = map[string]interface{}{"result": text}
 				}
-
 				respBytes, _ := json.Marshal(responseObj)
 
 				parts = append(parts, GeminiPart{
@@ -115,6 +117,8 @@ func (p *GeminiProvider) ChatCompletion(ctx context.Context, req *models.Unified
 						Response: json.RawMessage(respBytes),
 					},
 				})
+				i = j // Advance outer loop
+			}
 		} else {
 			for _, cp := range msg.Content {
 				if cp.Type == "text" {
@@ -208,6 +212,10 @@ func (p *GeminiProvider) ChatCompletion(ctx context.Context, req *models.Unified
 	}
 
 	if !resp.IsSuccess() {
+		fmt.Printf("[Gemini] API Error %d: %s\n", resp.StatusCode(), resp.String())
+		// Also log the request body for debugging (careful with API keys if logged elsewhere)
+		reqJSON, _ := json.Marshal(body)
+		fmt.Printf("[Gemini] Request Body: %s\n", string(reqJSON))
 		return nil, fmt.Errorf("Gemini API error (%d): %s", resp.StatusCode(), resp.String())
 	}
 
@@ -292,7 +300,8 @@ func (p *GeminiProvider) ChatCompletion(ctx context.Context, req *models.Unified
 func (p *GeminiProvider) ChatCompletionStream(ctx context.Context, req *models.UnifiedRequest) (<-chan *models.ChatCompletionStreamResponse, error) {
 	// Simplified Gemini mapping
 	var contents []GeminiContent
-	for _, msg := range req.Messages {
+	for i := 0; i < len(req.Messages); i++ {
+		msg := req.Messages[i]
 		role := "user"
 		if msg.Role == "assistant" {
 			role = "model"
@@ -303,13 +312,15 @@ func (p *GeminiProvider) ChatCompletionStream(ctx context.Context, req *models.U
 		var parts []GeminiPart
 		
 		if msg.Role == "tool" {
+			for j := i; j < len(req.Messages) && req.Messages[j].Role == "tool"; j++ {
+				m := req.Messages[j]
 				text := ""
-			if len(msg.Content) > 0 {
+				if len(m.Content) > 0 {
-				text = msg.Content[0].Text
+					text = m.Content[0].Text
 				}
-			name := "unknown"
+				name := "unknown_function"
-			if msg.Name != nil {
+				if m.Name != nil {
-				name = *msg.Name
+					name = *m.Name
 				}
 				
 				var responseObj interface{}
@@ -324,9 +335,21 @@ func (p *GeminiProvider) ChatCompletionStream(ctx context.Context, req *models.U
 						Response: json.RawMessage(respBytes),
 					},
 				})
+				i = j
+			}
 		} else {
 			for _, p := range msg.Content {
+				if p.Type == "text" {
 					parts = append(parts, GeminiPart{Text: p.Text})
+				} else if p.Image != nil {
+					base64Data, mimeType, _ := p.Image.ToBase64()
+					parts = append(parts, GeminiPart{
+						InlineData: &GeminiInlineData{
+							MimeType: mimeType,
+							Data:     base64Data,
+						},
+					})
+				}
 			}
 			if msg.Role == "assistant" && len(msg.ToolCalls) > 0 {
 				for _, tc := range msg.ToolCalls {