<!-- Thanks for the PR. A short description and the checklist below
are usually enough. For anything non-trivial, please link the issue
where direction was agreed. -->

## What this changes

<!-- One or two sentences. What does this PR do and why? -->

## Checklist

- [ ] Tests added or updated
- [ ] `cargo fmt --check` and `cargo clippy -- -D warnings` pass locally
- [ ] `CHANGELOG.md` updated if this is a user-visible change
- [ ] If AI tools drafted or materially shaped this change, disclosed
  in the description above
- [ ] Linked issue, discussion, or a short note explaining the
  motivation

## DynamoDB compatibility note (delete if not applicable)

<!-- Does this change Dynoxide's observable behaviour relative to AWS
DynamoDB? If yes, summarise the difference and link the AWS doc or
behaviour note that motivates it. -->
