The guard that only worked because something else was broken
Two defects were cancelling each other out. Fixing the real one on its own would have woken a dormant guard with the wrong logic and made the page worse.
Scott Mallinson
24notes from production work
I build software end to end. I'm Scott Mallinson, a software engineer at Travelport in Barcelona, Spain. I write about API design, type systems, guardrails for AI features, and the maintenance that keeps a codebase navigable.
- Role
- Software engineer
- At
- Travelport
- Based
- Barcelona
- Notes
- 24 published
Contents Page 1 of 4
A passing test that never saw the page
The tests for a desktop app's auto-scrolling passed the whole time the scrolling was broken: jsdom has no layout engine, so every height it reports is zero.
Four boundaries an AI assistant's guardrails have to cover
Validating user input is the most familiar guardrail and the smallest part of the problem. The model's own output, what it hands to tools, and what gets rendered afterwards all need the same fail-closed treatment.
What a promotion actually asserts
For an AI feature with guardrails, releasing it carefully requires two disciplines: coordinating multi-service promotions with evidence at each step, and keeping the validation environment faithful enough that human feedback can be trusted.
What AI features force you to specify
When you add an AI layer to a retrieval feature, data decisions that developers used to make by instinct become explicit contract requirements. Live demos are often the first place you find out which ones are missing.
An agent that plans feature flag removals, and the rule that keeps it safe
An agent that plans feature flag removals is useful. The rule about which flags it may never touch is what makes it safe to leave running, and what let the job move to the person who actually wants it done.