The measure-once design missed a host restyled from sized to height:auto after mount WITH in-flow content: it
stayed sized at its content height instead of getting the floor back, as the old probe did.
- After mount, follow() re-probes only when the reading says the host may have changed kind: floor on and the
host shorter than the floor (styled after mount, or capped), or floor off and the host changed size (it may now
follow its content). The re-probe saves every scrolled descendant (through shadow roots) and puts it back
before the frame paints, so no reader state is lost. A window-height change on a content-sized host still
writes nothing.
- A host capped below the floor (max-height) is latched by the probe that finds it, until it reaches the floor
again, so it is never re-probed in a loop. The 1 s post-flip window is gone.
- check:host-floor gains arm H (sized → auto with 420 px of content: the floor returns, at most one flip, the
scrolled child keeps its scrollTop) and counts re-probes in D/E. Poisons: the old per-resize probe, no capped
latch, no re-check of a sized host, no scroll restore.
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