expose skipped-record count from `list()`

> Adding a required field can make list() return no records until migration, per the docs. Could it expose a skipped-record count? Then an app could say '12 records need updating' instead of showing users an empty workspace.
> https://bsky.app/profile/uomasiri.bsky.social/post/3mvjabl7rsc2i

Start by locating the implementation and callers of `list()` and reproduce the documented case where a required field causes records to be skipped before migration. Determine how the skipped-record count should be exposed alongside the returned records; done means an app can distinguish an empty result from records needing updates and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.