fix(openai): preserve current Codex compact payload fields

backend/internal/service/openai_gateway_service.go

@@ -4864,7 +4864,18 @@ func normalizeOpenAICompactRequestBody(body []byte) ([]byte, bool, error) {
 	}
 
 	normalized := []byte(`{}`)
-	for _, field := range []string{"model", "input", "instructions", "previous_response_id"} {
+	// Keep the current Codex /compact schema while still dropping request-scoped
+	// fields such as prompt_cache_key, store, and stream.
+	for _, field := range []string{
+		"model",
+		"input",
+		"instructions",
+		"tools",
+		"parallel_tool_calls",
+		"reasoning",
+		"text",
+		"previous_response_id",
+	} {
 		value := gjson.GetBytes(body, field)
 		if !value.Exists() {
 			continue

backend/internal/service/openai_gateway_service_test.go

@@ -1767,6 +1767,24 @@ func TestOpenAIResponsesRequestPathSuffix(t *testing.T) {
 	}
 }
 
+func TestNormalizeOpenAICompactRequestBodyPreservesCurrentCodexPayloadFields(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.5","input":[{"type":"message","role":"user","content":"compact me"}],"instructions":"compact-test","tools":[{"type":"function","name":"shell"}],"parallel_tool_calls":true,"reasoning":{"effort":"high"},"text":{"verbosity":"low"},"previous_response_id":"resp_123","store":true,"stream":true,"prompt_cache_key":"cache_123"}`)
+
+	normalized, changed, err := normalizeOpenAICompactRequestBody(body)
+
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Equal(t, "gpt-5.5", gjson.GetBytes(normalized, "model").String())
+	require.True(t, gjson.GetBytes(normalized, "tools").Exists())
+	require.True(t, gjson.GetBytes(normalized, "parallel_tool_calls").Bool())
+	require.Equal(t, "high", gjson.GetBytes(normalized, "reasoning.effort").String())
+	require.Equal(t, "low", gjson.GetBytes(normalized, "text.verbosity").String())
+	require.Equal(t, "resp_123", gjson.GetBytes(normalized, "previous_response_id").String())
+	require.False(t, gjson.GetBytes(normalized, "store").Exists())
+	require.False(t, gjson.GetBytes(normalized, "stream").Exists())
+	require.False(t, gjson.GetBytes(normalized, "prompt_cache_key").Exists())
+}
+
 func TestOpenAIBuildUpstreamRequestOpenAIPassthroughPreservesCompactPath(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	rec := httptest.NewRecorder()