refactor: Use helper to extract wrapped "thinking" text

Improve robustness when handling "thinking" content by using a dedicated helper to extract the thinking text. This ensures wrapped or nested thinking objects are handled correctly instead of relying on a direct string extraction, reducing parsing errors for complex payloads.

internal/translator/antigravity/claude/antigravity_claude_request.go

@@ -118,7 +118,8 @@ func ConvertClaudeRequestToAntigravity(modelName string, inputRawJSON []byte, _
 					contentResult := contentResults[j]
 					contentTypeResult := contentResult.Get("type")
 					if contentTypeResult.Type == gjson.String && contentTypeResult.String() == "thinking" {
-						thinkingText := contentResult.Get("thinking").String()
+						// Use GetThinkingText to handle wrapped thinking objects
+						thinkingText := util.GetThinkingText(contentResult)
 						signatureResult := contentResult.Get("signature")
 						signature := ""
 						if signatureResult.Exists() && signatureResult.String() != "" {

internal/util/thinking_text.go

@@ -0,0 +1,87 @@
+package util
+
+import (
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+// GetThinkingText extracts the thinking text from a content part.
+// Handles various formats:
+// - Simple string: { "thinking": "text" } or { "text": "text" }
+// - Wrapped object: { "thinking": { "text": "text", "cache_control": {...} } }
+// - Gemini-style: { "thought": true, "text": "text" }
+// Returns the extracted text string.
+func GetThinkingText(part gjson.Result) string {
+	// Try direct text field first (Gemini-style)
+	if text := part.Get("text"); text.Exists() && text.Type == gjson.String {
+		return text.String()
+	}
+
+	// Try thinking field
+	thinkingField := part.Get("thinking")
+	if !thinkingField.Exists() {
+		return ""
+	}
+
+	// thinking is a string
+	if thinkingField.Type == gjson.String {
+		return thinkingField.String()
+	}
+
+	// thinking is an object with inner text/thinking
+	if thinkingField.IsObject() {
+		if inner := thinkingField.Get("text"); inner.Exists() && inner.Type == gjson.String {
+			return inner.String()
+		}
+		if inner := thinkingField.Get("thinking"); inner.Exists() && inner.Type == gjson.String {
+			return inner.String()
+		}
+	}
+
+	return ""
+}
+
+// GetThinkingTextFromJSON extracts thinking text from a raw JSON string.
+func GetThinkingTextFromJSON(jsonStr string) string {
+	return GetThinkingText(gjson.Parse(jsonStr))
+}
+
+// SanitizeThinkingPart normalizes a thinking part to a canonical form.
+// Strips cache_control and other non-essential fields.
+// Returns the sanitized part as JSON string.
+func SanitizeThinkingPart(part gjson.Result) string {
+	// Gemini-style: { thought: true, text, thoughtSignature }
+	if part.Get("thought").Bool() {
+		result := `{"thought":true}`
+		if text := GetThinkingText(part); text != "" {
+			result, _ = sjson.Set(result, "text", text)
+		}
+		if sig := part.Get("thoughtSignature"); sig.Exists() && sig.Type == gjson.String {
+			result, _ = sjson.Set(result, "thoughtSignature", sig.String())
+		}
+		return result
+	}
+
+	// Anthropic-style: { type: "thinking", thinking, signature }
+	if part.Get("type").String() == "thinking" || part.Get("thinking").Exists() {
+		result := `{"type":"thinking"}`
+		if text := GetThinkingText(part); text != "" {
+			result, _ = sjson.Set(result, "thinking", text)
+		}
+		if sig := part.Get("signature"); sig.Exists() && sig.Type == gjson.String {
+			result, _ = sjson.Set(result, "signature", sig.String())
+		}
+		return result
+	}
+
+	// Not a thinking part, return as-is but strip cache_control
+	return StripCacheControl(part.Raw)
+}
+
+// StripCacheControl removes cache_control and providerOptions from a JSON object.
+func StripCacheControl(jsonStr string) string {
+	result := jsonStr
+	result, _ = sjson.Delete(result, "cache_control")
+	result, _ = sjson.Delete(result, "providerOptions")
+	return result
+}