One database, two front doors

Our trade-show operation lived in a 12-tab Excel workbook. It had no audit trail or safe way for two people to edit at once, and adding a second conference was going to be a problem. I also wanted an agent to read and update event data through controlled operations.

I built a Postgres database shared by a private Next.js app and a Claude MCP connector. The app uses magic-link sign-in with a database-enforced email allowlist. The connector exposes 92 tools across 16 domains behind an OAuth 2.1 server I built into the app, including PKCE, dynamic client registration and refresh-token reuse detection. Both use the same data layer. Every change gets an immutable audit row with before/after values and its channel, web or Claude. Destructive agent actions need a second confirmation: a caller-bound HMAC token that expires in five minutes. Read tools return secret metadata and vault pointers, never the secrets.

The team uses it daily, the workbook is gone, and the app is past v1.0.60. An operator can click through the app or ask Claude to add a lead at booth 1234. Both create the same audited row. Another conference needs a new slug. The spreadsheet importer had its own problems to solve: emails saved as hyperlink objects, phone numbers in scientific notation and featured rows identified only by cell color. It also found a plaintext credential and moved it into vault storage.