In summary, RRDP files (snapshots and deltas) declare URIs for their contained files (RPKI objects), and there's nothing in the standard preventing a malicious CA's RRDP file from declaring a URI that will cause the validator to override some other CA's RPKI object. So the RP needs to create per-RPP namespaces.
Fort's namespaces ("workspaces") are TAL-scoped. This prevents RPPs from different trees from overriding each other, but not RPPs from the same tree.
This is the original problem.
In summary, RRDP files (snapshots and deltas) declare URIs for their contained files (RPKI objects), and there's nothing in the standard preventing a malicious CA's RRDP file from declaring a URI that will cause the validator to override some other CA's RPKI object. So the RP needs to create per-RPP namespaces.
Fort's namespaces ("workspaces") are TAL-scoped. This prevents RPPs from different trees from overriding each other, but not RPPs from the same tree.
Branch rrdp-refactor has a WIP of this bug.