feat: support responses compaction payload compatibility for codex translator

internal/translator/codex/openai/responses/codex_openai-responses_request.go

@@ -2,6 +2,7 @@ package responses
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
@@ -26,6 +27,8 @@ func ConvertOpenAIResponsesRequestToCodex(modelName string, inputRawJSON []byte,
 	rawJSON, _ = sjson.DeleteBytes(rawJSON, "temperature")
 	rawJSON, _ = sjson.DeleteBytes(rawJSON, "top_p")
 	rawJSON, _ = sjson.DeleteBytes(rawJSON, "service_tier")
+	rawJSON, _ = sjson.DeleteBytes(rawJSON, "truncation")
+	rawJSON = applyResponsesCompactionCompatibility(rawJSON)
 
 	// Delete the user field as it is not supported by the Codex upstream.
 	rawJSON, _ = sjson.DeleteBytes(rawJSON, "user")
@@ -36,6 +39,43 @@ func ConvertOpenAIResponsesRequestToCodex(modelName string, inputRawJSON []byte,
 	return rawJSON
 }
 
+// applyResponsesCompactionCompatibility handles OpenAI Responses context_management.compaction
+// for Codex upstream compatibility.
+//
+// Codex /responses currently rejects context_management with:
+// {"detail":"Unsupported parameter: context_management"}.
+//
+// Compatibility strategy:
+// 1) Remove context_management before forwarding to Codex upstream.
+// 2) Remove truncation as Codex upstream currently rejects it as unsupported.
+func applyResponsesCompactionCompatibility(rawJSON []byte) []byte {
+	contextManagement := gjson.GetBytes(rawJSON, "context_management")
+	if !contextManagement.Exists() {
+		return rawJSON
+	}
+
+	hasCompactionRule := false
+	switch {
+	case contextManagement.IsArray():
+		for _, item := range contextManagement.Array() {
+			if strings.EqualFold(item.Get("type").String(), "compaction") {
+				hasCompactionRule = true
+				break
+			}
+		}
+	case contextManagement.IsObject():
+		hasCompactionRule = strings.EqualFold(contextManagement.Get("type").String(), "compaction")
+	}
+
+	if hasCompactionRule {
+		// no-op marker: compaction hint detected and consumed for compatibility.
+	}
+
+	rawJSON, _ = sjson.DeleteBytes(rawJSON, "context_management")
+	rawJSON, _ = sjson.DeleteBytes(rawJSON, "truncation")
+	return rawJSON
+}
+
 // convertSystemRoleToDeveloper traverses the input array and converts any message items
 // with role "system" to role "developer". This is necessary because Codex API does not
 // accept "system" role in the input array.

internal/translator/codex/openai/responses/codex_openai-responses_request_test.go

@@ -280,3 +280,41 @@ func TestUserFieldDeletion(t *testing.T) {
 		t.Errorf("user field should be deleted, but it was found with value: %s", userField.Raw)
 	}
 }
+
+func TestContextManagementCompactionCompatibility(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gpt-5.2",
+		"context_management": [
+			{
+				"type": "compaction",
+				"compact_threshold": 12000
+			}
+		],
+		"input": [{"role":"user","content":"hello"}]
+	}`)
+
+	output := ConvertOpenAIResponsesRequestToCodex("gpt-5.2", inputJSON, false)
+	outputStr := string(output)
+
+	if gjson.Get(outputStr, "context_management").Exists() {
+		t.Fatalf("context_management should be removed for Codex compatibility")
+	}
+	if gjson.Get(outputStr, "truncation").Exists() {
+		t.Fatalf("truncation should be removed for Codex compatibility")
+	}
+}
+
+func TestTruncationRemovedForCodexCompatibility(t *testing.T) {
+	inputJSON := []byte(`{
+		"model": "gpt-5.2",
+		"truncation": "disabled",
+		"input": [{"role":"user","content":"hello"}]
+	}`)
+
+	output := ConvertOpenAIResponsesRequestToCodex("gpt-5.2", inputJSON, false)
+	outputStr := string(output)
+
+	if gjson.Get(outputStr, "truncation").Exists() {
+		t.Fatalf("truncation should be removed for Codex compatibility")
+	}
+}