1Assign selection colors to users. goals:
 2    * current user is always main color
 3    * every other user has the same color in every context
 4    * users don't need to be in a shared project to have a color. they can either be in the call, or in a channel notes.
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 6Places colors are used:
 7    * editor element, driven by the buffer's `remote_selections`
 8    * pane border (access to more state)
 9    * collab titlebar (access to more state)
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11Currently, editor holds an optional "replica id map".
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13Most challenging part is in the editor, because the editor should be fairly self-contained, not depend on e.g. the user store.
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