ACI-054: A Fold Is a Rewrite with an Error Rate

Thesis

A fold compacts a durable working record so the next session reads less, and because it rewrites that record, it has an error rate. Measure it in bytes, cut by execution rather than age, verify it mechanically rather than by reading it, and then check the fold's own new text against the archive, the one thing no fold checks.

Story

A fold's output is what the next session reads. On Laksa one agent's fold cut its status board from 14,293 to 8,123 bytes and reported itself complete, yet the next session's pickup still read 79KB, because the message files read at pickup were not on the board (Laksa@3c9f41b77, 2026-09-01). The honest number can be small. An aggressive fold on Intent took a board from 114,252 to 109,874 bytes, 4%, because 86% of the board was watch-outs that the protocol keeps, and claiming more "would be the vanity metric". The same fold nearly buried an unexecuted hold sitting in the region it was cutting, and caught it "because the rule is execution and not age" (Intent@bab38a9f3, 2026-09-05).