feat(translator): add tests to validate trailing assistant prefill stripping and sanitize tool call IDs

- Introduced tests for `ConvertOpenAIRequestToGemini`, `ConvertOpenAIResponsesRequestToGemini`, and related Claude functions to ensure trailing model-prefill turns are removed.
- Enhanced tool call ID handling with `util.SanitizeClaudeToolID` to standardize IDs in Claude-related conversions and tests.
- Updated logic in Gemini and Claude translators to handle edge cases for trailing assistant prefill and tool ID sanitization, ensuring compatibility across input variants.

Closes: router-for-me#3113

Author: luispater

internal/translator/claude/openai/chat-completions/claude_openai_request.go

@@ -16,6 +16,7 @@ import (
 	"github.com/google/uuid"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
@@ -212,6 +213,7 @@ func ConvertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream
 							if toolCallID == "" {
 								toolCallID = genToolCallID()
 							}
+							toolCallID = util.SanitizeClaudeToolID(toolCallID)
 
 							function := toolCall.Get("function")
 							toolUse := []byte(`{"type":"tool_use","id":"","name":"","input":{}}`)
@@ -247,6 +249,7 @@ func ConvertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream
 			case "tool":
 				// Handle tool result messages conversion
 				toolCallID := message.Get("tool_call_id").String()
+				toolCallID = util.SanitizeClaudeToolID(toolCallID)
 				toolContentResult := message.Get("content")
 
 				msg := []byte(`{"role":"user","content":[{"type":"tool_result","tool_use_id":"","content":""}]}`)

internal/translator/claude/openai/chat-completions/claude_openai_request_test.go

@@ -6,6 +6,44 @@ import (
 	"github.com/tidwall/gjson"
 )
 
+func TestConvertOpenAIRequestToClaude_SanitizesToolCallIDsForClaude(t *testing.T) {
+	inputJSON := `{
+		"model": "gpt-4.1",
+		"messages": [
+			{
+				"role": "assistant",
+				"tool_calls": [
+					{
+						"id": "call.with space:1",
+						"type": "function",
+						"function": {
+							"name": "Read",
+							"arguments": "{\"path\":\"README.md\"}"
+						}
+					}
+				]
+			},
+			{
+				"role": "tool",
+				"tool_call_id": "call.with space:1",
+				"content": "ok"
+			}
+		]
+	}`
+
+	result := ConvertOpenAIRequestToClaude("claude-sonnet-4-5", []byte(inputJSON), false)
+	resultJSON := gjson.ParseBytes(result)
+	toolUseID := resultJSON.Get("messages.0.content.0.id").String()
+	toolResultID := resultJSON.Get("messages.1.content.0.tool_use_id").String()
+
+	if toolUseID != "call_with_space_1" {
+		t.Fatalf("tool_use id = %q, want %q", toolUseID, "call_with_space_1")
+	}
+	if toolResultID != toolUseID {
+		t.Fatalf("tool_result tool_use_id = %q, want same sanitized id %q", toolResultID, toolUseID)
+	}
+}
+
 func TestConvertOpenAIRequestToClaude_ToolResultTextAndBase64Image(t *testing.T) {
 	inputJSON := `{
 		"model": "gpt-4.1",

internal/translator/claude/openai/responses/claude_openai-responses_request.go

@@ -12,6 +12,7 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/registry"
 	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/thinking"
+	"github.com/router-for-me/CLIProxyAPI/v7/internal/util"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
@@ -371,6 +372,7 @@ func ConvertOpenAIResponsesRequestToClaude(modelName string, inputRawJSON []byte
 				if callID == "" {
 					callID = genToolCallID()
 				}
+				callID = util.SanitizeClaudeToolID(callID)
 				name := item.Get("name").String()
 				argsStr := item.Get("arguments").String()
 
@@ -399,6 +401,7 @@ func ConvertOpenAIResponsesRequestToClaude(modelName string, inputRawJSON []byte
 				flushPendingReasoning()
 				// Map to user tool_result
 				callID := item.Get("call_id").String()
+				callID = util.SanitizeClaudeToolID(callID)
 				flushPendingToolUseFor(callID)
 				outputStr := item.Get("output").String()
 				toolResult := []byte(`{"type":"tool_result","tool_use_id":"","content":""}`)

internal/translator/claude/openai/responses/claude_openai-responses_request_test.go

@@ -9,6 +9,37 @@ import (
 	"google.golang.org/protobuf/encoding/protowire"
 )
 
+func TestConvertOpenAIResponsesRequestToClaude_SanitizesToolCallIDsForClaude(t *testing.T) {
+	inputJSON := `{
+		"model": "gpt-4.1",
+		"input": [
+			{
+				"type": "function_call",
+				"call_id": "call.with space:1",
+				"name": "Read",
+				"arguments": "{\"path\":\"README.md\"}"
+			},
+			{
+				"type": "function_call_output",
+				"call_id": "call.with space:1",
+				"output": "ok"
+			}
+		]
+	}`
+
+	result := ConvertOpenAIResponsesRequestToClaude("claude-sonnet-4-5", []byte(inputJSON), false)
+	resultJSON := gjson.ParseBytes(result)
+	toolUseID := resultJSON.Get("messages.0.content.0.id").String()
+	toolResultID := resultJSON.Get("messages.1.content.0.tool_use_id").String()
+
+	if toolUseID != "call_with_space_1" {
+		t.Fatalf("tool_use id = %q, want %q", toolUseID, "call_with_space_1")
+	}
+	if toolResultID != toolUseID {
+		t.Fatalf("tool_result tool_use_id = %q, want same sanitized id %q", toolResultID, toolUseID)
+	}
+}
+
 func TestConvertOpenAIResponsesRequestToClaude_ReasoningItemToThinkingBlock(t *testing.T) {
 	rawSignature, expectedSignature := testClaudeResponsesThinkingSignature(t)
 	raw := []byte(`{

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

@@ -294,6 +294,16 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 		}
 	}
 
+	// Gemini/Vertex accepts assistant/model turns in history, but some model
+	// surfaces reject requests whose final turn is model-authored prefill.
+	contents := gjson.GetBytes(out, "contents")
+	if contents.Exists() && contents.IsArray() {
+		arr := contents.Array()
+		if len(arr) > 0 && arr[len(arr)-1].Get("role").String() == "model" {
+			out, _ = sjson.DeleteBytes(out, fmt.Sprintf("contents.%d", len(arr)-1))
+		}
+	}
+
 	// tools -> tools[].functionDeclarations + tools[].googleSearch/codeExecution/urlContext passthrough
 	tools := gjson.GetBytes(rawJSON, "tools")
 	if tools.IsArray() && len(tools.Array()) > 0 {

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

@@ -0,0 +1,28 @@
+package chat_completions
+
+import (
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func TestConvertOpenAIRequestToGemini_StripsTrailingAssistantPrefill(t *testing.T) {
+	inputJSON := `{
+		"model": "gpt-5.4",
+		"messages": [
+			{"role": "user", "content": "hello"},
+			{"role": "assistant", "content": "previous answer"}
+		]
+	}`
+
+	result := ConvertOpenAIRequestToGemini("gemini-3.1-pro-high", []byte(inputJSON), false)
+	resultJSON := gjson.ParseBytes(result)
+	contents := resultJSON.Get("contents").Array()
+
+	if len(contents) != 1 {
+		t.Fatalf("contents length = %d, want 1. contents=%s", len(contents), resultJSON.Get("contents").Raw)
+	}
+	if got := contents[0].Get("role").String(); got != "user" {
+		t.Fatalf("final remaining role = %q, want %q", got, "user")
+	}
+}

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

@@ -2,6 +2,7 @@ package responses
 
 import (
 	"encoding/json"
+	"fmt"
 	"strings"
 
 	sigcompat "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
@@ -369,6 +370,16 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 		out, _ = sjson.SetRawBytes(out, "contents.-1", userContent)
 	}
 
+	// Gemini/Vertex accepts assistant/model turns in history, but some model
+	// surfaces reject requests whose final turn is model-authored prefill.
+	contents := gjson.GetBytes(out, "contents")
+	if contents.Exists() && contents.IsArray() {
+		arr := contents.Array()
+		if len(arr) > 0 && arr[len(arr)-1].Get("role").String() == "model" {
+			out, _ = sjson.DeleteBytes(out, fmt.Sprintf("contents.%d", len(arr)-1))
+		}
+	}
+
 	// Convert tools to Gemini functionDeclarations format
 	if tools := root.Get("tools"); tools.Exists() && tools.IsArray() {
 		geminiTools := []byte(`[{"functionDeclarations":[]}]`)

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

@@ -9,6 +9,35 @@ import (
 
 const testResponsesGeminiThoughtSignature = "EjQKMgEMOdbHO0Gd+c9Mxk4ELwPGbpCEcp2mFfYYLix2UVtBH3fL8GECc4+JITVnHF4qZDsA"
 
+func TestConvertOpenAIResponsesRequestToGemini_StripsTrailingAssistantPrefill(t *testing.T) {
+	inputJSON := `{
+		"model": "gpt-5.4",
+		"input": [
+			{
+				"type": "message",
+				"role": "user",
+				"content": [{"type": "input_text", "text": "hello"}]
+			},
+			{
+				"type": "message",
+				"role": "assistant",
+				"content": [{"type": "output_text", "text": "previous answer"}]
+			}
+		]
+	}`
+
+	result := ConvertOpenAIResponsesRequestToGemini("gemini-3.1-pro-high", []byte(inputJSON), false)
+	resultJSON := gjson.ParseBytes(result)
+	contents := resultJSON.Get("contents").Array()
+
+	if len(contents) != 1 {
+		t.Fatalf("contents length = %d, want 1. contents=%s", len(contents), resultJSON.Get("contents").Raw)
+	}
+	if got := contents[0].Get("role").String(); got != "user" {
+		t.Fatalf("final remaining role = %q, want %q", got, "user")
+	}
+}
+
 func TestConvertOpenAIResponsesRequestToGemini_ReasoningSignatureCompatibility(t *testing.T) {
 	tests := []struct {
 		name          string