← Zach Donnenfield

Method

The story, then the build

Every project starts with a written case for why it should exist. AI models write most of the code from there, and I am responsible for the decisions, the testing and the call to ship.

The method in one view

I trained as a journalist and spent years in content and research before building products. I still work like a reporter. I check the first account against a second source, reconcile evidence that disagrees, and follow a feature request back to the problem underneath it.

The written case has three parts, shown below. Its last question, how we will know, becomes the test plan for the build.

Start with

Customer evidence

The reason

Write the story

  1. Situation

    What is true now, for whom, and what it costs while it stays true.

  2. Complication

    What has kept it that way, and why earlier fixes did not stick.

  3. Resolution

    What will be different for the customer, and how we will know.

The behavior

Build against it

  1. 01

    Draft

    The model produces the first pass. I read every line before it lands.

  2. 02

    Evaluate

    I decide what gets tested, starting with the failures that would stay silent.

  3. 03

    Harden

    I test hostile inputs, missing data, accessibility, reversibility and runtime fallbacks.

  4. 04

    Attack

    A separate adversarial pass hunts for poisoned state, lost edits and interactions that fail under real use.

Ship gate

The reason and the behavior both have to survive review.

From customer evidence to release.

Where judgment stays human

Before Segment Atlas, I had never decoded a binary ride file, parsed a geospatial raster or built a 3D scene. Models got me through that quickly. They did not decide that recorded results stay primary, that estimates carry confidence labels, or that an oversized route is refused before any data is fetched. I made those calls.

Stage

I own

The model contributes

Frame

I own

Which problem is worth solving, and the evidence behind it.

The model contributes

Research breadth, alternate framings and counterexamples.

Design

I own

Architecture, tradeoffs, data contracts and the decisions users will feel.

The model contributes

Implementation options, first drafts and refactors.

Evaluate

I own

Failure inventory and test criteria.

The model contributes

Test scaffolding, fuzz cases and review breadth.

Ship

I own

Trust UX, reversibility and the final release decision.

The model contributes

Documentation and cleanup.

Where it went wrong

The mistakes that matter look plausible. These four come from Segment Atlas and the internal AI suite.

Mistake

What happened

What changed

Math that looks right

Segment Atlas

What happened

Averaging wind directions of 350° and 10° gives 180°, due south. A model drafts that confidently, and a quick review passes it.

What changed

Wind is interpolated as vectors, and a test pins that exact case to north.

Read the test ↗

A theory that measurement disproved

Internal AI suite

What happened

Heavy reports failed intermittently. My first theory, too many calls at once, pointed to a fix that would have made it worse.

What changed

I measured the retry behavior first. The real limit was the cost of each request, so heavy requests now split by brand. A 63-part report runs in 27 seconds.

Tests that passed when they should not have

Internal AI suite

What happened

Twice, a regression check passed because its test data had been built from files that were already trimmed.

What changed

Test inputs are now padded to full size, and each check is compared against live output before its results count.

A number too wrong to ship

Internal AI suite

What happened

One brand’s monthly figure came back about 130 times higher than the client’s delivered file.

What changed

I left the brand out with a visible note. It was confirmed and added back five days later through configuration, with no code change.

Check the work

The Segment Atlas code is public, tests included. The case studies show the same method on enterprise work, and two more are available on request.