Grid: AnimateRows uses the row geometry or refuses content-sized mode

Context

This is leaf L5 of epic #19658, blocked by #19661 (the geometry model). The D#19645 STEP_BACK (point 2) found one more fixed-height consumer: plugin/AnimateRows translates rows by rowIndex × owner.rowHeight (L160, dev bf91293bde).

The Problem

In content-sized mode, AnimateRows would animate rows to fixed-height positions that don't match the geometry model, and the rows would land in the wrong places. The epic does not accept a silent fixed-height fallback.

Found at intake: the plugin does not work in fixed-height mode either. A sort or a filter throws owner.createRow is not a function, because the pooled grid.Body has no createRow any more. The plugin also keys rows by vdom id, while the body's vdom root now holds Row component references. Its repair is a rewrite onto the Row pool, tracked in #6858.

The Fix

Choose one at intake and record why:

• (a) AnimateRows reads row offsets from the geometry model when the mode is on, so sort and filter animations land on the real offsets;
• (b) the combination is refused explicitly: enabling content-sized mode with AnimateRows raises a clear error, or a documented warning plus the plugin disabling itself, never a silent wrong layout.

Chosen at intake: (b). (a) presupposes a plugin that works with the pooled Body, and that is the #6858 rewrite, not a geometry read. In content-sized mode, the plugin's store handlers (which shadow grid.Body#onStoreFilter and #onStoreLoad on the body instance) run the Body's own handlers and warn once that animatedRowSorting is ignored with contentSizedRows. Rows then render at their geometry offsets through the normal path. This works in either order, plugin first or mode first, and nothing has to be uninstalled.

Contract Ledger

Acceptance Criteria

• In content-sized mode, AnimateRows refuses the combination explicitly: a spec shows the warning, and rows land at the geometry's prefix offsets after a sort and a filter.
• In fixed-height mode, the plugin's code path is unchanged. No AnimateRows specs exist; its fixed-height breakage is #6858's scope.

Out of Scope

Every other consumer (L1, L4), the 100k journey (L6), and repairing the plugin for the pooled Body (#6858).

Related

#19658 · #19661 (blocked by) · #6858 · D#19645 STEP_BACK (18881069)

Origin Session ID: daac81df-5205-405e-a3af-aec56e5cca45