fix(codex): normalize null instructions for compact requests

internal/runtime/executor/codex_executor.go

@@ -220,7 +220,8 @@ func (e *CodexExecutor) executeCompact(ctx context.Context, auth *cliproxyauth.A
 	body = applyPayloadConfigWithRoot(e.cfg, baseModel, to.String(), "", body, originalTranslated, requestedModel)
 	body, _ = sjson.SetBytes(body, "model", baseModel)
 	body, _ = sjson.DeleteBytes(body, "stream")
-	if !gjson.GetBytes(body, "instructions").Exists() {
+	instructions := gjson.GetBytes(body, "instructions")
+	if !instructions.Exists() || instructions.Type == gjson.Null {
 		body, _ = sjson.SetBytes(body, "instructions", "")
 	}
 

internal/runtime/executor/codex_executor_compact_test.go

@@ -15,6 +15,22 @@ import (
 )
 
 func TestCodexExecutorCompactAddsDefaultInstructions(t *testing.T) {
+	cases := []struct {
+		name    string
+		payload string
+	}{
+		{
+			name:    "missing instructions",
+			payload: `{"model":"gpt-5.4","input":"hello"}`,
+		},
+		{
+			name:    "null instructions",
+			payload: `{"model":"gpt-5.4","instructions":null,"input":"hello"}`,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
 			var gotPath string
 			var gotBody []byte
 			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -34,7 +50,7 @@ func TestCodexExecutorCompactAddsDefaultInstructions(t *testing.T) {
 
 			resp, err := executor.Execute(context.Background(), auth, cliproxyexecutor.Request{
 				Model:   "gpt-5.4",
-		Payload: []byte(`{"model":"gpt-5.4","input":"hello"}`),
+				Payload: []byte(tc.payload),
 			}, cliproxyexecutor.Options{
 				SourceFormat: sdktranslator.FromString("openai-response"),
 				Alt:          "responses/compact",
@@ -49,10 +65,15 @@ func TestCodexExecutorCompactAddsDefaultInstructions(t *testing.T) {
 			if !gjson.GetBytes(gotBody, "instructions").Exists() {
 				t.Fatalf("expected instructions in compact request body, got %s", string(gotBody))
 			}
+			if gjson.GetBytes(gotBody, "instructions").Type != gjson.String {
+				t.Fatalf("instructions type = %v, want string", gjson.GetBytes(gotBody, "instructions").Type)
+			}
 			if gjson.GetBytes(gotBody, "instructions").String() != "" {
 				t.Fatalf("instructions = %q, want empty string", gjson.GetBytes(gotBody, "instructions").String())
 			}
 			if string(resp.Payload) != `{"id":"resp_1","object":"response.compaction","usage":{"input_tokens":1,"output_tokens":2,"total_tokens":3}}` {
 				t.Fatalf("payload = %s", string(resp.Payload))
 			}
+		})
+	}
 }