F1c (exit-heavy): DomCascade.pending() aggregates the items' finished so the owner Presence holds the subtree until the exit cascade settles (PresenceOptions.pending, Presence.startPhase). beginEnter drives the enter from the off-state with the transition suppressed (items mount in the on-state, so a passive mirror would ease toward off instead of jumping). pending() settles each finisher (then(noop,noop)) so one cancelled row can't collapse the wait.
F2: wire the children-DOM cascade into the real dropdown-menu. Content part declares animation.surface+staggerChildren; provider routes an opt-in 'animation' prop, runs a DomCascade over getCascadeRows (every visible row incl. disabled), forwards a pending hook through the floating shell. Coexistence fixes surfaced by the menu: item rows hand their transition to the cascade-* preset via a higher-specificity rule (longhands keep the stagger delay); disabled opacity gated off during the cascade; the panel's own dismiss-fade signature suppressed in cascade mode (data-cascade) so it doesn't fade the panel before the rows finish; the trigger is excluded from the menu's dismissal so the toggle closes (pre-existing bug). Verified in a real browser (Playwright): enter+exit cascade with reversed stagger, all four close methods, disabled row fades. dom-cascade 9/9, check 0 new errors.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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