feat(executor): centralize systemInstruction handling for Claude and Gemini-3-Pro models

fix(executor): update gemini model identifier to gemini-3-pro-preview

internal/runtime/executor/antigravity_executor.go

@@ -45,6 +45,7 @@ const (
 	defaultAntigravityAgent        = "antigravity/1.104.0 darwin/arm64"
 	antigravityAuthType            = "antigravity"
 	refreshSkew                    = 3000 * time.Second
+	systemInstruction              = "You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding.You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.**Absolute paths only****Proactiveness**"
 )
 
 var (
@@ -1047,11 +1048,11 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 		payload = []byte(strJSON)
 	}
 
-	if strings.Contains(modelName, "claude") || strings.Contains(modelName, "gemini-3-pro") {
+	if strings.Contains(modelName, "claude") || strings.Contains(modelName, "gemini-3-pro-preview") {
 		systemInstructionPartsResult := gjson.GetBytes(payload, "request.systemInstruction.parts")
-
 		payload, _ = sjson.SetBytes(payload, "request.systemInstruction.role", "user")
-		payload, _ = sjson.SetBytes(payload, "request.systemInstruction.parts.0.text", "You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding.You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.**Absolute paths only****Proactiveness**")
+		payload, _ = sjson.SetBytes(payload, "request.systemInstruction.parts.0.text", systemInstruction)
+		payload, _ = sjson.SetBytes(payload, "request.systemInstruction.parts.1.text", fmt.Sprintf("Please ignore following [ignore]%s[/ignore]", systemInstruction))
 
 		if systemInstructionPartsResult.Exists() && systemInstructionPartsResult.IsArray() {
 			for _, partResult := range systemInstructionPartsResult.Array() {