**feat(translator): add ThoughtSignature handling in Gemini request transformations**

internal/interfaces/client_models.go

@@ -62,6 +62,9 @@ type Part struct {
 	// InlineData contains base64-encoded data with its MIME type (e.g., images).
 	InlineData *InlineData `json:"inlineData,omitempty"`
 
+	// ThoughtSignature is a provider-required signature that accompanies certain parts.
+	ThoughtSignature string `json:"thoughtSignature,omitempty"`
+
 	// FunctionCall represents a tool call requested by the model.
 	FunctionCall *FunctionCall `json:"functionCall,omitempty"`
 

internal/translator/gemini-cli/claude/gemini-cli_claude_request.go

@@ -17,6 +17,8 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+const geminiCLIClaudeThoughtSignature = "skip_thought_signature_validator"
+
 // ConvertClaudeRequestToCLI parses and transforms a Claude Code API request into Gemini CLI API format.
 // It extracts the model name, system instruction, message contents, and tool declarations
 // from the raw JSON request and returns them in the format expected by the Gemini CLI API.
@@ -89,7 +91,10 @@ func ConvertClaudeRequestToCLI(modelName string, inputRawJSON []byte, _ bool) []
 						functionArgs := contentResult.Get("input").String()
 						var args map[string]any
 						if err := json.Unmarshal([]byte(functionArgs), &args); err == nil {
-							clientContent.Parts = append(clientContent.Parts, client.Part{FunctionCall: &client.FunctionCall{Name: functionName, Args: args}})
+							clientContent.Parts = append(clientContent.Parts, client.Part{
+								FunctionCall:     &client.FunctionCall{Name: functionName, Args: args},
+								ThoughtSignature: geminiCLIClaudeThoughtSignature,
+							})
 						}
 					} else if contentTypeResult.Type == gjson.String && contentTypeResult.String() == "tool_result" {
 						toolCallID := contentResult.Get("tool_use_id").String()

internal/translator/gemini-cli/openai/chat-completions/gemini-cli_openai_request.go

@@ -15,6 +15,8 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+const geminiCLIFunctionThoughtSignature = "skip_thought_signature_validator"
+
 // ConvertOpenAIRequestToGeminiCLI converts an OpenAI Chat Completions request (raw JSON)
 // into a complete Gemini CLI request JSON. All JSON construction uses sjson and lookups use gjson.
 //
@@ -239,6 +241,7 @@ func ConvertOpenAIRequestToGeminiCLI(modelName string, inputRawJSON []byte, _ bo
 							fargs := tc.Get("function.arguments").String()
 							node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.name", fname)
 							node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
+							node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", geminiCLIFunctionThoughtSignature)
 							p++
 							if fid != "" {
 								fIDs = append(fIDs, fid)

internal/translator/gemini/claude/gemini_claude_request.go

@@ -17,6 +17,8 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+const geminiClaudeThoughtSignature = "skip_thought_signature_validator"
+
 // ConvertClaudeRequestToGemini parses a Claude API request and returns a complete
 // Gemini CLI request body (as JSON bytes) ready to be sent via SendRawMessageStream.
 // All JSON transformations are performed using gjson/sjson.
@@ -82,7 +84,10 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 						functionArgs := contentResult.Get("input").String()
 						var args map[string]any
 						if err := json.Unmarshal([]byte(functionArgs), &args); err == nil {
-							clientContent.Parts = append(clientContent.Parts, client.Part{FunctionCall: &client.FunctionCall{Name: functionName, Args: args}})
+							clientContent.Parts = append(clientContent.Parts, client.Part{
+								FunctionCall:     &client.FunctionCall{Name: functionName, Args: args},
+								ThoughtSignature: geminiClaudeThoughtSignature,
+							})
 						}
 					} else if contentTypeResult.Type == gjson.String && contentTypeResult.String() == "tool_result" {
 						toolCallID := contentResult.Get("tool_use_id").String()

internal/translator/gemini/openai/chat-completions/gemini_openai_request.go

@@ -15,6 +15,8 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+const geminiFunctionThoughtSignature = "skip_thought_signature_validator"
+
 // ConvertOpenAIRequestToGemini converts an OpenAI Chat Completions request (raw JSON)
 // into a complete Gemini request JSON. All JSON construction uses sjson and lookups use gjson.
 //
@@ -264,6 +266,7 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 							fargs := tc.Get("function.arguments").String()
 							node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".functionCall.name", fname)
 							node, _ = sjson.SetRawBytes(node, "parts."+itoa(p)+".functionCall.args", []byte(fargs))
+							node, _ = sjson.SetBytes(node, "parts."+itoa(p)+".thoughtSignature", geminiFunctionThoughtSignature)
 							p++
 							if fid != "" {
 								fIDs = append(fIDs, fid)

internal/translator/gemini/openai/responses/gemini_openai-responses_request.go

@@ -10,6 +10,8 @@ import (
 	"github.com/tidwall/sjson"
 )
 
+const geminiResponsesThoughtSignature = "skip_thought_signature_validator"
+
 func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte, stream bool) []byte {
 	rawJSON := bytes.Clone(inputRawJSON)
 
@@ -108,6 +110,7 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 				modelContent := `{"role":"model","parts":[]}`
 				functionCall := `{"functionCall":{"name":"","args":{}}}`
 				functionCall, _ = sjson.Set(functionCall, "functionCall.name", name)
+				functionCall, _ = sjson.Set(functionCall, "thoughtSignature", geminiResponsesThoughtSignature)
 
 				// Parse arguments JSON string and set as args object
 				if arguments != "" {