Split the 8178-line scanner.rs (48% inline tests) into a canonical
scanner.rs + scanner/ module tree with zero behavior change:
- scanner.rs (~2140): cycle constants, schedule status, budget/config
helpers, startup, maintenance features, the two run loops, and
cycle-result finalization
- scanner/activity.rs (~770): wake/backoff policy and scanner activity
observation (probing, generations, topology digest)
- scanner/heal_info.rs (~110): the background-heal info object
- scanner/cycle_state.rs (~500): cycle-state codec, persisted usage
floors, and cycle-state persistence
- scanner/leadership.rs (~360): leader-lock claiming, usage-epoch
fencing, and lock-loss handling
- scanner/usage_store.rs (~480): the CAS data-usage store pipeline and
observed-snapshot cleanup
- scanner/tests.rs (~3920): the inline test module as a child module
All crate paths are unchanged: scanner::BackgroundHealInfo,
scanner::read_background_heal_info, scanner::store_data_usage_in_backend,
and scanner_topology_digest resolve through root re-exports with their
original visibilities, and the pub(crate) surface used by scanner_io and
remote_scanner re-exports at pub(crate). Cross-module items gain
pub(super), whose scope equals the old single-module privacy domain.
Code is moved verbatim apart from those markers, per-module import
headers, and rustfmt re-wraps.
Co-authored-by: heihutu <[email protected]>
