perf(go): skip empty parsed raw payloads

go/vehicle-gateway/internal/history/writer.go

@@ -72,7 +72,7 @@ func (w *Writer) AppendRawFrame(ctx context.Context, env envelope.FrameEnvelope)
 	}
 	rawHex, rawHexChunks := chunkPayload(env, "raw_hex", env.RawHex)
 	rawText, rawTextChunks := chunkPayload(env, "raw_text", env.RawText)
-	parsedJSON, parsedChunks := chunkPayload(env, "parsed_json", jsonString(env.Parsed))
+	parsedJSON, parsedChunks := chunkPayload(env, "parsed_json", parsedJSONString(env.Parsed))
 	_, err := w.exec.ExecContext(ctx, fmt.Sprintf(`INSERT INTO %s
   (ts, frame_id, event_id, message_id, event_time, received_at, raw_size_bytes,
    raw_hex, raw_text, parsed_json, parse_status, parse_error, source_endpoint)
@@ -317,6 +317,13 @@ func jsonString(value any) string {
 	return string(data)
 }
 
+func parsedJSONString(value map[string]any) string {
+	if len(value) == 0 {
+		return ""
+	}
+	return jsonString(value)
+}
+
 func floatField(env envelope.FrameEnvelope, key string) (float64, bool) {
 	if env.Fields == nil {
 		return 0, false

go/vehicle-gateway/internal/history/writer_test.go

@@ -126,6 +126,27 @@ func TestWriterChunksOversizedParsedJSON(t *testing.T) {
 	}
 }
 
+func TestWriterLeavesParsedJSONEmptyWhenNoParsedPayload(t *testing.T) {
+	exec := &recordingExec{}
+	writer := NewWriter(exec)
+	env := sampleEnvelope()
+	env.Parsed = nil
+	env.ParseStatus = envelope.ParseBadFrame
+	env.ParseError = "invalid frame checksum"
+
+	if err := writer.AppendRawFrame(context.Background(), env); err != nil {
+		t.Fatalf("AppendRawFrame() error = %v", err)
+	}
+
+	rawInsert := findSQL(exec.calls, "INSERT INTO raw_")
+	if strings.Contains(rawInsert, "'{}'") || strings.Contains(rawInsert, "'null'") {
+		t.Fatalf("raw insert should not store empty parsed_json payload: %s", rawInsert)
+	}
+	if !strings.Contains(rawInsert, "'invalid frame checksum'") {
+		t.Fatalf("raw insert should keep parse error: %s", rawInsert)
+	}
+}
+
 func TestWriterSkipsSparseDerivedRows(t *testing.T) {
 	exec := &recordingExec{}
 	writer := NewWriter(exec)