docs(adr): ADR-0045 — additive materialization with a visibility gate; drafts narrow to mutations

Accepted 2026-06-12. Additive builds materialize real artifacts immediately
(hidden app = the gate; publish = visibility flip); the ADR-0027 draft
workspace narrows to mutations of published artifacts. Evidence: the
2026-06-12 preview-chain audit (five second-world adaptation defects) and
the unfinished P3 data plane. Resolves discard (trash-can + 7-day GC),
hidden-app API exposure (fully dark + ADR-0039 preview tokens later), and
the implicit-reachability additivity clause. v1 scope: magic moment on rails.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: os-zhuang