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d5e8f79cf4
When scheduling the initial root and when using `unstable_scheduleHydration` we should use the Hydration Lanes rather than the raw update lane. This ensures that we're always hydrating using a Hydration Lane or the Offscreen Lane rather than other lanes getting some random hydration in it. This fixes an issue where updating a root while it is still hydrating causes it to trigger client rendering when it could just hydrate and then apply the update on top of that. It also fixes a potential performance issue where `unstable_scheduleHydration` gets batched with an update that then ends up forcing an update of a boundary that requires it to rewind to do the hydration lane anyway. Might as well just start with the hydration without the update applied first. I added a kill switch (`enableHydrationLaneScheduling`) just in case but seems very safe given that using `unstable_scheduleHydration` at all is very rare and updating the root before the shell hydrates is extremely rare (and used to trigger a recoverable error).