Function discovery_block_bytes 

pub const fn discovery_block_bytes() -> u64

The active discovery-block size in bytes.

Production reads the fixed DISCOVERY_BLOCK_BYTES constant — this accessor inlines to it, so the block geometry is byte-identical to naming the constant directly. Test builds that enable the test-support feature get an overridable value instead (see override_discovery_block_bytes_for_test), so a loopback test can drive the block-spanning planner with tiny blocks and tiny blobs rather than the 64 MiB a real two-block blob would need.