If objects are rejected from willFilterPage(), they should be didRejectResult()'d before being discarded. Without this, handles won't be able to distinguish between unknown and filtered results, and may render "Unknown Object (Diffusion Commit)" instead of "Restricted Diffusion Commit".
Just throwing this in Maniphest so I don't forget about it; see IRC.
@mbishopim3 reported users being confused about "Unknown Object" emails, and particularly thinking that they were erroneous. These are supposed to say "Restricted Task" / "Restricted Revision", etc., not "Unknown Object", so that's an issue at a minimum.
Beyond that, we may want to improve the wording on these emails (e.g., if the mail renders handles which are restricted, include a note like "You don't have permission to see some of the objects discussed in this email.").
I wasn't able to reproduce this immediately yesterday, but got pulled off after like two seconds of poking at it.