CutoverProof

Inspiration

AI agents can propose production changes faster than engineers can safely review them. But an online database migration can look correct step by step and still fail when old and new application versions overlap during cutover.

We built CutoverProof to test whether an agent can help prepare a high-stakes migration review without receiving the power to execute or approve it.

What it does

CutoverProof is a shared change contract for online PostgreSQL migrations.

A WebMCP browser agent can inspect a declared migration contract, identify risk areas, and create a structured review draft. The engineer then explicitly starts a bounded sandbox assessment. PostgreSQL executes only declared operations in a disposable database and checks read-only invariants for concrete counterexamples.

The authority boundary is deliberate: the agent prepares, PostgreSQL verifies, and the engineer authorizes consequential actions.

How we built it

We built an authenticated React workspace with five typed WebMCP browser tools registered through document.modelContext.registerTool.

The tools use closed JSON schemas and validated FastAPI endpoints to let an agent inspect migration contracts, prepare a review, read verified evidence, and open a human repair review. The deterministic verifier runs against a disposable PostgreSQL sandbox. The app is deployed on Google Cloud Run.

Challenges we ran into

The hardest challenge was making WebMCP genuinely useful without turning it into an unsafe automation bypass.

We needed the agent to understand structured contracts and evidence, while ensuring it could not start an assessment, execute arbitrary SQL, alter a verdict, approve a repair, or deploy anything. We also had to keep the handoff visible: an agent-created review must appear in the engineer’s workspace and explicitly wait for human action.

Accomplishments that we're proud of

• Built five authenticated, typed WebMCP tools for a real browser-agent workflow.
• Created a visible agent → verifier → human handoff, rather than hidden automation.
• Kept PostgreSQL as the independent source of evidence and verdicts.
• Enforced clear safety boundaries: no tool can start execution or approve a repair.
• Deployed a working live product with deterministic migration evidence and repair replay.

What we learned

WebMCP is most powerful when it exposes structured product capabilities, not when it merely automates clicks.

We learned that agent assistance becomes more trustworthy when authority is explicit: agents prepare context, deterministic systems verify claims, and humans retain control over consequential decisions.

What's next for CutoverProof

We will expand from structured PostgreSQL migration packs toward richer real-world migration inputs, while preserving the same safety model: declared contracts, bounded experiments, independent verification, human authorization, and portable evidence.

The broader goal is a trust layer for agent-assisted production changes—not a system that gives agents unchecked production power.

Built With

• docker
• fastapi
• gemini
• google-cloud-build
• google-cloud-run
• postgresql
• pydantic
• pytest
• python
• react
• typescript
• vertex-ai
• vite
• webmcp