One scan updates every client that has the app open.
The problem
Stock lived across five separate storage units with no system of record. Answering what was in which unit, or where a box had ended up mid-move, meant walking the floor and asking whoever was around.
What I built
Every box gets a QR label, and scanning it is the whole job. Scan in the van and the box goes In Transit; scan at the door and it records the warehouse and the room it landed in.
Postgres holds the state. Each change goes out over a realtime subscription to whoever has the app open, so nobody refreshes to get a current count.
Take a box out and its line items come off the count with it. The numbers track the shelf instead of the last spreadsheet anyone edited.
I put the API in its own Cloudflare Worker with a bot Worker beside it, which keeps the integration surface out of the client app.
Dashboards and exports over the item history: sortable tables, charts, generated PDFs.