---
title: "My strict re-land of the LIKE exemption still had a bypass"
canonical: https://dxdev.com/blog/narrow-exemption-opus-review-reverted/
datePublished: 2026-10-03
---
I landed a safety-guard exemption at 4:53 PM on October 3rd and wrote in the commit that real tables would still be refused. Sixteen minutes later I had reverted it.

## Why the guard refuses a leading wildcard

The guard sits in front of production database access and refuses scan-shaped queries. A leading-wildcard LIKE against a real table in prod is the query you want stopped before it runs.

## The exemption I landed

`sys.*` and `INFORMATION_SCHEMA.*` are catalog views, which are not real tables. A leading-wildcard LIKE against them is harmless, but the guard refused it anyway. So I added an exemption that allows the LIKE when it is confined to catalog views. I wrote tests and committed it with this message: "any real-table target still refused."

That sentence was wrong.

## The BLOCKER

The revert commit cites an Opus review BLOCKER. The exemption let real-table LIKEs through, which was exactly what my message said it would not do.

I reverted it, and the revert message says why: it let real-table LIKEs through. Then I re-landed it strict. Every FROM and JOIN now had to be directly followed by a catalog name. A comma join, a comment, a quoted or dynamic name, APPLY, a write, EXEC or string building all made the guard refuse the query again.

It still wasn't enough. The second Opus review found another bypass.

The four commits, in order:

1. Exempt catalog-view LIKEs.
2. Revert: real-table LIKEs got through.
3. Re-land the exemption, strict.
4. Withdraw the exemption entirely.

## Withdrawing it

I withdrew the exemption. The guard is back to fully strict, with no catalog carve-out at all. The bypass cases stay in the test suite as tests that assert they are blocked, so the suite keeps a record of what got through.

Review found a hole in the "narrow" rule twice, and the second withdrawal came at 5:30 PM.

## What stays

A leading-wildcard LIKE against a catalog view is refused again. The bypass cases stay in the test suite as blocked tests.