A trace is a fold, not a second file

A session keeps one durable record. The operational trace that stood beside it, transcript.jsonl, is deleted outright rather than retired to a filtered projection of the log: an operational view is a fold of record.jsonl like every other durable artifact, and a fact the log’s vocabulary has no home for is named a loss rather than kept alive by a second file. This pays in full the two-record debt recording-follows-the-event booked and one-seam-one-log paid by half.

Why the second record could not be folded

one-seam-one-log unified the durable half — the model view and the resumed scrollback became folds of record.jsonl — and left the trace an independently written file, fed at the bus emit seam outside that change’s boundary. That is still two authorities for one session, which is the shape 260623’s debt names; retiring the trace to a projection would have kept the file and only changed who wrote it. The question a decision has to answer is not where the second record is written but whether the session has anything left that only it holds.

It has three facts, and each has a truer home in the one log:

• A per-line clock becomes the log line’s own Entry.at_unix_ms (exarch/src/record.rs). Entry is private to the log module — a fold sees a bare Record — so the clock is a property of the line, not of the vocabulary, and no projection can come to depend on it.
• A child’s born/died are its own Protocol::SessionStarted and Protocol::SessionEnded bookends in its own log, where a child’s lifetime was always recorded.
• stop_reason already rides Protocol::AssistantMessage; the trace held a copy.

The accepted loss

/resources’ pressure figures. No session keeps a pressure history, so the figures the trace could answer from are not answerable from the log — this is named a loss, not deferred to a fold that cannot exist. Restoring them means recording pressure as a fact, which is a decision this one does not make.

What this does not decide

The same change moved Kind’s variants into four homes. Where code lives is map/, not a decision — nothing here rests on that move, and it needs no page of its own.