The initial sync fuzzer suites run a series of randomized operations against the sync source of an initial syncing node in a way that is highly deterministic and reproducible. The diversity of operation types that it runs, however, is low, since it relies on a simplified grammar for generating operations (both CRUD ops and DDL ops). To give us thorough coverage of initial sync bugs that require more complex operation types, we should extend the grammar of the initial sync fuzzer to include all document shapes we can reasonably include in the grammar, and also include create/drop index operations with all index shapes. This should give us more thorough and reproducible coverage of initial sync.
Our existing jstestfuzz_replication_initsync suites give us coverage of initial sync with good operation diversity, but those failures can be much harder to reproduce due to the inherent non-determinism of the BackgroundInitialSync test hook.