Fixed gemini system prompt handling

pkg/lmcli/provider/google/google.go

@@ -159,7 +159,6 @@ func createGenerateContentRequest(
 
 	request := &GenerateContentRequest{
 		Contents: requestContents,
-		SystemInstructions: system,
 		GenerationConfig: &GenerationConfig{
 			MaxOutputTokens: &params.MaxTokens,
 			Temperature:     &params.Temperature,
@@ -167,6 +166,16 @@ func createGenerateContentRequest(
 		},
 	}
 
+	if system != "" {
+		request.SystemInstruction = Content{
+			Parts: []ContentPart{
+				{
+					Text: system,
+				},
+			},
+		}
+	}
+
 	if len(params.ToolBag) > 0 {
 		request.Tools = convertTools(params.ToolBag)
 	}

pkg/lmcli/provider/google/types.go

@@ -36,7 +36,7 @@ type GenerationConfig struct {
 type GenerateContentRequest struct {
 	Contents          []Content         `json:"contents"`
 	Tools             []Tool            `json:"tools,omitempty"`
-	SystemInstructions string            `json:"systemInstructions,omitempty"`
+	SystemInstruction *Content          `json:"systemInstruction,omitempty"`
 	GenerationConfig  *GenerationConfig `json:"generationConfig,omitempty"`
 }