fix(translator): normalize and restrict stop_reason/finish_reason usage

- Standardized the handling of `stop_reason` and `finish_reason` across Codex and Gemini responses.
- Restricted pass-through of specific reasons (`max_tokens`, `stop`) for consistency.
- Enhanced fallback logic for undefined reasons.

internal/translator/codex/claude/codex_claude_response.go

@@ -113,10 +113,10 @@ func ConvertCodexResponseToClaude(_ context.Context, _ string, originalRequestRa
 		template = `{"type":"message_delta","delta":{"stop_reason":"tool_use","stop_sequence":null},"usage":{"input_tokens":0,"output_tokens":0}}`
 		p := (*param).(*ConvertCodexResponseToClaudeParams).HasToolCall
 		stopReason := rootResult.Get("response.stop_reason").String()
-		if stopReason != "" {
+		if p {
-			template, _ = sjson.Set(template, "delta.stop_reason", stopReason)
-		} else if p {
 			template, _ = sjson.Set(template, "delta.stop_reason", "tool_use")
+		} else if stopReason == "max_tokens" || stopReason == "stop" {
+			template, _ = sjson.Set(template, "delta.stop_reason", stopReason)
 		} else {
 			template, _ = sjson.Set(template, "delta.stop_reason", "end_turn")
 		}

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

@@ -78,11 +78,16 @@ func ConvertCliResponseToOpenAI(_ context.Context, _ string, originalRequestRawJ
 		template, _ = sjson.Set(template, "id", responseIDResult.String())
 	}
 
-	// Extract and set the finish reason.
+	finishReason := ""
-	if finishReasonResult := gjson.GetBytes(rawJSON, "response.candidates.0.finishReason"); finishReasonResult.Exists() {
+	if stopReasonResult := gjson.GetBytes(rawJSON, "response.stop_reason"); stopReasonResult.Exists() {
-		template, _ = sjson.Set(template, "choices.0.finish_reason", strings.ToLower(finishReasonResult.String()))
+		finishReason = stopReasonResult.String()
-		template, _ = sjson.Set(template, "choices.0.native_finish_reason", strings.ToLower(finishReasonResult.String()))
 	}
+	if finishReason == "" {
+		if finishReasonResult := gjson.GetBytes(rawJSON, "response.candidates.0.finishReason"); finishReasonResult.Exists() {
+			finishReason = finishReasonResult.String()
+		}
+	}
+	finishReason = strings.ToLower(finishReason)
 
 	// Extract and set usage metadata (token counts).
 	if usageResult := gjson.GetBytes(rawJSON, "response.usageMetadata"); usageResult.Exists() {
@@ -197,6 +202,12 @@ func ConvertCliResponseToOpenAI(_ context.Context, _ string, originalRequestRawJ
 	if hasFunctionCall {
 		template, _ = sjson.Set(template, "choices.0.finish_reason", "tool_calls")
 		template, _ = sjson.Set(template, "choices.0.native_finish_reason", "tool_calls")
+	} else if finishReason != "" && (*param).(*convertCliResponseToOpenAIChatParams).FunctionIndex == 0 {
+		// Only pass through specific finish reasons
+		if finishReason == "max_tokens" || finishReason == "stop" {
+			template, _ = sjson.Set(template, "choices.0.finish_reason", finishReason)
+			template, _ = sjson.Set(template, "choices.0.native_finish_reason", finishReason)
+		}
 	}
 
 	return []string{template}

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

@@ -129,11 +129,16 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 			candidateIndex := int(candidate.Get("index").Int())
 			template, _ = sjson.Set(template, "choices.0.index", candidateIndex)
 
-			// Extract and set the finish reason.
+			finishReason := ""
-			if finishReasonResult := candidate.Get("finishReason"); finishReasonResult.Exists() {
+			if stopReasonResult := gjson.GetBytes(rawJSON, "stop_reason"); stopReasonResult.Exists() {
-				template, _ = sjson.Set(template, "choices.0.finish_reason", strings.ToLower(finishReasonResult.String()))
+				finishReason = stopReasonResult.String()
-				template, _ = sjson.Set(template, "choices.0.native_finish_reason", strings.ToLower(finishReasonResult.String()))
 			}
+			if finishReason == "" {
+				if finishReasonResult := gjson.GetBytes(rawJSON, "candidates.0.finishReason"); finishReasonResult.Exists() {
+					finishReason = finishReasonResult.String()
+				}
+			}
+			finishReason = strings.ToLower(finishReason)
 
 			partsResult := candidate.Get("content.parts")
 			hasFunctionCall := false
@@ -225,6 +230,12 @@ func ConvertGeminiResponseToOpenAI(_ context.Context, _ string, originalRequestR
 			if hasFunctionCall {
 				template, _ = sjson.Set(template, "choices.0.finish_reason", "tool_calls")
 				template, _ = sjson.Set(template, "choices.0.native_finish_reason", "tool_calls")
+			} else if finishReason != "" {
+				// Only pass through specific finish reasons
+				if finishReason == "max_tokens" || finishReason == "stop" {
+					template, _ = sjson.Set(template, "choices.0.finish_reason", finishReason)
+					template, _ = sjson.Set(template, "choices.0.native_finish_reason", finishReason)
+				}
 			}
 
 			responseStrings = append(responseStrings, template)