R1:c42c5983aa6a

Fix an issue where loading a mangled project graph could fail too abruptly

Summary:
Ref T13484. If you load a subproject S which has a mangled/invalid `parentPath`, the query currently tries to execute an empty edge query and fatals.

Instead, we want to deny-by-default in the policy layer but not fail the query. The subproject should become restricted but not fatal anything related to it.

See T13484 for a future refinement where we could identify "broken / data integrity issue" objects explicilty.

Test…