The problem

Harbor's four product teams had each built their own component layer. The libraries agreed on nothing, and every cross-team feature paid a translation tax. Two previous attempts at a shared system had been announced, adopted by one team, and abandoned.

What we did

We started from what the teams already had rather than from a blank file. Every component in the new system began as the most-used variant of the four existing ones, so adoption meant deleting code rather than rewriting it. The token layer landed first and independently: teams could adopt colour and spacing without touching a single component. By the time we shipped components, three of the four teams were already on the tokens.

What made it stick

Nobody was told to migrate. The system was faster to use than the thing it replaced, and the teams that adopted it early were visibly shipping faster. The fourth team migrated on its own six weeks later.