Address commentary in manifest.excludedmanifestrevlog.add - specifically we should improve the collaboration with core so that add() never gets called on an excluded directory and we can improve the stand-in to raise a ProgrammingError.

Reason more completely about rename-filtering logic in narrowfilelog. There could be some surprises lurking there.

Formally document the narrowspec format. For bonus points, unify with the server-specified narrowspec format.

narrowrepo.setnarrowpats() or narrowspec.save() need to make sure they're holding the wlock.

The follinwg places do an unrestricted dirstate walk (including files outside the narrowspec). Some of them should perhaps not do that.

• debugfileset
• perfwalk
• sparse (but restricted to sparse config)
• largefiles