Module diff 

State Diff Engine: field-level change tracking.

Captures before/after snapshots of account data and computes diffs. Use cases:

• Audit trails
• Test assertions
• Post-mutation invariant verification
• Debugging state transitions

Usage

// Capture before state
let snap = StateSnapshot::<256>::capture(account_data);

// ... mutations happen ...

// Compute diff
let diff = snap.diff(account_data);
if diff.has_changes() {
    let regions = diff.changed_regions::<8>();
    let mut i = 0;
    while i < regions.len() {
        if let Some(r) = regions.get(i) {
            // r.offset, r.length
        }
        i += 1;
    }
}

Design

Snapshots are stack-allocated using const generics. The maximum snapshot size is a compile-time parameter. For accounts larger than the snapshot buffer, only the first N bytes are captured. Use was_truncated() to detect this.

Structs

ChangedRegion

A contiguous region of changed bytes.

ChangedRegionIter

Iterator over changed regions.

ChangedRegions

Stack-allocated list of changed regions.

StateDiff

A diff between two states of account data.

StateSnapshot

A stack-allocated snapshot of account data.

Functions

field_diff_mask

Build a field-level diff report for a known layout.