The audit of test coverage flagged three holes:
- `omnigraph optimize` and `omnigraph cleanup` had no integration tests
(no `maintenance.rs`). Add one covering empty/idempotent edges, the
policy-validation contract on `cleanup`, and head preservation under
aggressive policies.
- `apply_schema` only covered I32 -> I64 type-change rejection. Add the
symmetric narrowing case plus rejections for the other destructive
shapes (drop property with data, drop node type, drop edge type, add
required property without backfill) and assert the manifest version
doesn't advance. Add a positive `@rename_from` case to pin the
stable-type-id contract preserves rows through a rename.
- `docs/testing.md` was missing `validators.rs` and the new
`maintenance.rs` from its file table; bump the count and add rows.
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