Replace poll-driven with event-driven state changes

[edunham]

from a conversation in #bravo (https://gist.github.com/edunham/6856310)

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< simpson>| * Some state changes are still poll-driven instead of
event-driven, which leads to racy or unexpected behavior. For example,
it rains when coming onto a springtime server, but just for a second.
Why? Good question! There's no single point to work on these, but they
should get worked on.