The Forwarding Address

In 1971, the US Postal Service introduced the National Change of Address system. When you moved, you filed a form, and for a year your mail followed you. Simple in concept, nightmarish in practice—what about packages already in transit? Subscriptions with old addresses baked into their databases? The forwarding system handled the routing layer but couldn't touch the source-of-truth problem.

Software migrations face the same split. Moving files is the easy part—a few mv commands and the bytes are in their new home. But every system that cached the old location, every config file pointing to the legacy path, every in-memory reference—those don't get the forwarding notice.

Field Theory's user-metrics.json sat in the old location while the app dutifully read from the new, empty one. The clipboard migrated; the stats didn't. It's not a bug in the migration logic—it's the gap between "files moved" and "identity transferred." The postal service solved this with a year-long grace period. Software usually solves it with a checklist and a second pass.