Commit an `AddSource(Embedded)` retired delta for each given resource, making it the highest- precedence fallback. Skips resources that already have an `Embedded` source or no longer exist. Used on a throwaway session clone at export time so the exported registry and history agree; callers must guarantee the bytes are available in the export's resource store.
(&mut self, ids: impl IntoIterator<Item = ResourceId>)
source not stored for this graph (policy: none)