Function diff_normalized 

pub fn diff_normalized(
    a: &Snapshot,
    b: &Snapshot,
    plan: &MapPlan,
    opts: DiffOpts,
) -> SnapshotDiff

Compare a against b with b’s origins read through plan, and roll the result up per subject.

b’s rows are rewritten before the comparison — the origin chunk by the plan’s pairs, the base onto a’s stated base, the holder’s origin with the key’s, and the identity bridge’s host_id (RFC 06 §6.2) with the origin it restates — and then compared exactly as diff_snapshots would. A stamp that moved alone is not a change here (DiffOpts::stamps_alone).

Over a plan with anything unmapped the comparison is not made: the report carries the pairs it had, every unpaired origin with its reason, and by_subject not asked — SnapshotDiff::refused, the reserved non-verdict.