Discriminant — lets snapshot consumers detect marker entries.
OptionalpreviewFirst SUMMARY_PREVIEW_LENGTH chars — primitives and strings only.
OptionalsizeSize proxy: string length, array length, or object key count.
typeof result, refined to 'array' / 'null' for objects.
Marker recorded in
StageSnapshot.stageReadsunderreadTracking: 'summary'.Honest cost note:
sizeis a cheap proxy (string length / array length / object key count), NOT a serialized byte count — computing real byte size would require an O(value) serialization, which is exactly the cost the summary mode removes.previewis only produced for primitives and strings (first SUMMARY_PREVIEW_LENGTH characters); objects and arrays carry no preview for the same reason.