fix(claude): honor disable_parallel_tool_use

internal/translator/codex/claude/codex_claude_request.go

@@ -271,8 +271,14 @@ func ConvertClaudeRequestToCodex(modelName string, inputRawJSON []byte, _ bool)
 		}
 	}
 
+	// Default to parallel tool calls unless the client explicitly disables them.
+	parallelToolCalls := true
+	if disableParallelToolUse := rootResult.Get("disable_parallel_tool_use"); disableParallelToolUse.Exists() {
+		parallelToolCalls = !disableParallelToolUse.Bool()
+	}
+
 	// Add additional configuration parameters for the Codex API.
-	template, _ = sjson.Set(template, "parallel_tool_calls", true)
+	template, _ = sjson.Set(template, "parallel_tool_calls", parallelToolCalls)
 
 	// Convert thinking.budget_tokens to reasoning.effort.
 	reasoningEffort := "medium"

internal/translator/codex/claude/codex_claude_request_test.go

@@ -87,3 +87,49 @@ func TestConvertClaudeRequestToCodex_SystemMessageScenarios(t *testing.T) {
 		})
 	}
 }
+
+func TestConvertClaudeRequestToCodex_ParallelToolCalls(t *testing.T) {
+	tests := []struct {
+		name                  string
+		inputJSON             string
+		wantParallelToolCalls bool
+	}{
+		{
+			name: "Default to true when disable_parallel_tool_use is absent",
+			inputJSON: `{
+				"model": "claude-3-opus",
+				"messages": [{"role": "user", "content": "hello"}]
+			}`,
+			wantParallelToolCalls: true,
+		},
+		{
+			name: "Disable parallel tool calls when client opts out",
+			inputJSON: `{
+				"model": "claude-3-opus",
+				"disable_parallel_tool_use": true,
+				"messages": [{"role": "user", "content": "hello"}]
+			}`,
+			wantParallelToolCalls: false,
+		},
+		{
+			name: "Keep parallel tool calls enabled when client explicitly allows them",
+			inputJSON: `{
+				"model": "claude-3-opus",
+				"disable_parallel_tool_use": false,
+				"messages": [{"role": "user", "content": "hello"}]
+			}`,
+			wantParallelToolCalls: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := ConvertClaudeRequestToCodex("test-model", []byte(tt.inputJSON), false)
+			resultJSON := gjson.ParseBytes(result)
+
+			if got := resultJSON.Get("parallel_tool_calls").Bool(); got != tt.wantParallelToolCalls {
+				t.Fatalf("parallel_tool_calls = %v, want %v. Output: %s", got, tt.wantParallelToolCalls, string(result))
+			}
+		})
+	}
+}