Problem

Operation.inverse(...) was part of the documented utility surface, but set_selection in slate-v2 only carried the next selection:

{ type: 'set_selection', selection: next }

That makes inversion fake. There is no previous state to swap back to.

Root Cause

The transaction engine had narrowed set_selection for convenience, but the public operation utility layer still implied true inversion semantics.

That mismatch is small, but it is a real contract bug.

Solution

Restore set_selection to carry both sides:

{
  type: 'set_selection',
  properties: previous,
  newProperties: next,
}

Then:

• build all internal selection ops through one helper
• apply newProperties in the core reducer
• let Operation.inverse(...) swap the two sides directly

Why This Works

Selection inversion becomes honest again because the operation itself now owns the full state transition.

It also gives history/debug tooling a better operation record instead of a write-only next-state blob.

Prevention

• If an operation claims to be invertible, it must carry enough information to actually invert.
• Do not collapse an operation payload just because the reducer only needs the destination state.
• Small utility layers rot fast when nobody asks whether the data shape still matches the claim.