We’ve all been in that meeting. The one where the exorbitant consultancy firm presents their “Digital Transformation Strategy.”
The slides are glossy. The promise is intoxicating. “We will use GenAI to modernize your 15-year-old Java monolith into cloud-native microservices in 6 months.”
Everyone nods. The CFO smiles at the potential cloud savings. The CTO breathes a sigh of relief that they might finally get off that unsupported version of Oracle.
Then the meeting ends, and the real panic sets in.
Because you know something the consultants don’t. You know that generating the code is the easy part.
The “Diff” Delusion
In the old world (circa 2022), we relied on git diff. A human wrote code, another human read the diff, nodded sage-like, and clicked Merge.
This worked because the changes were incremental. A new button here, a bug fix there.
But AI doesn’t do “incremental.” AI refactors entire subsystems before breakfast. It rewrites 5,000 lines of spaghetti code into clean, modern TypeScript in seconds.
Go ahead. Open that Pull Request. Look at the diff.
It’s completely red on the left, completely green on the right.
You can’t review that. No human can. You can’t “eyeball” a complete architectural shift. You are staring at a black box that claims to be your new billing system.
Does it handle the edge case from 2009 that Bob (who retired last year) hardcoded? Does it render correctly on the CEO’s iPad?
You have two choices:
- Trust the Unit Tests: Which, let’s be honest, the AI probably wrote too.
- Spin up a Staging Environment: And wait in line behind the 14 other teams fighting for “Staging-Alpha”.
The Bottleneck is Reality
The bottleneck in software engineering used to be typing. AI solved that. The bottleneck is now Verification.
We are generating code 100x faster than we can verify it. And for a Legacy Modernization project, “verification” doesn’t mean passing a linter. It means Behavioral Parity.
The new system must behave exactly like the old one, bugs and all, until you decide otherwise.
But you can’t test behavioral parity by reading code. You have to touch it. You have to click it. You have to break it.
Verification at the Speed of AI
This is why we built PrevHQ. Not because we needed another way to deploy a Hello World app, but because we were terrified of the code our own AI agents were writing.
We realized that for every PR, we needed a mirror.
- Legacy Branch: Deploys to
legacy-pr-123.prevhq.com - Modern Branch: Deploys to
modern-pr-123.prevhq.com
Side by side. Instant.
You don’t need to queue for a staging environment. You don’t need to ask DevOps to provision a new cluster.
You just open the PR, and the environment exists.
Now you can give that link to the QA lead, the Product Manager, or even the intense business stakeholder who knows exactly how the report should look.
Stop Reading, Start Clicking
The most dangerous lie in a migration project is “It works on my machine.” The second most dangerous is “The tests passed.”
Don’t settle for green checkmarks in a terminal. Demand a URL.
If your AI agents are writing code that you can’t run immediately, you aren’t modernizing. You’re just building a bigger legacy for someone else to clean up.