[2.0 / next] Content opened by a display-ahead Show attaches with the committed value instead of being born held #4697

Ruled-not-built row S-46 (the plain case) from #4695. The ruling is in packages/web/test/async-gen/rulings/S-46.ts. Rules: D-25, D-27, and Decision 4 in documentation/plans/optimism-seam-spike-brief.md §8.

Shape: detail = id + 1 is async. A plain write to id is held by detail's flight. <Show when={latest(id) > 0}> wraps content that reads id() plainly.

Ruled: the Show opens ahead because it asked latest. Its branch is a mount whose first pass read the staging plainly, so it is born held: the fallback stays, and the content attaches at the landing as vs0:1 vm0:2 vs0:1.

Today: the branch attaches at once with an empty hole for the inserted content. SCENARIOS.md recorded this ✗ row as fixed by #4574, so this may be a regression.

The rows are it.fails in rulings.spec.ts. Flip them to it when this is fixed.