TranscriptCodec

Reads and writes Transcript as JSON.

The wire is a small closed vocabulary — user, agent, activity — with times as epoch milliseconds and absent values simply left out. Written by hand rather than derived, so the shape is inspectable and stays identical on both platforms the contract is compiled for.

Reads are one-way tolerant: an entry whose kind this version does not know is dropped, so a page written by a newer writer still renders everything this reader understands instead of failing whole.