EstimatedSize

Estimate the serialized JSON byte size of a value without actually serializing it. Used on hot paths (enqueuing runs for batched tracing) where the exact serialized size is not required -- only a reasonable approximation for soft memory accounting.

Walks the object graph in O(n) without allocating a JSON string, avoiding the event-loop blocking that JSON.stringify causes on large payloads.

Accuracy notes (all estimates are approximate, never exact):

• Strings: UTF-8 byte length via Buffer.byteLength when available, falling back to code-unit length for non-Node environments. Does not account for escape expansion (", \, control chars, surrogate escapes) which is usually a small fraction of total size.
• Binary data (Buffer / typed arrays / ArrayBuffer / DataView): sized from their JSON.stringify representations where practical ({ type: "Buffer", data: [...] } for Buffer, keyed objects for typed arrays). DataView and ArrayBuffer themselves have no enumerable own properties and serialize as "{}". Each byte contributes ~3.5 characters on average in Buffer's decimal-array representation (digit(s) + comma).
• Other objects with toJSON(): we invoke toJSON() once and estimate the result. This matches JSON.stringify semantics for libraries like Decimal.js, Moment, Luxon, Mongoose documents, etc.
• Cycles: detected via an ancestor-path set that is pushed/popped during recursion. This matches JSON.stringify semantics -- repeated references that are not on the current ancestor chain (shared subobjects) are counted every time they appear, because JSON.stringify will serialize them every time.
• No depth limit (JSON.stringify has none either).