Brex: the Bottleneck Was Plumbing, Not the Model
Brex migrated gRPC client factories across 400+ services by giving every agent task its own remote developer environment and wiring CI, review bots, and test runners directly into the agent's loop. The lesson, in their words: the gap between "AI agents can do this" and "AI agents are doing this reliably" is mostly an infrastructure problem.
Brex is the candid build log of the assemble-it-yourself path. It is one of the in-house platforms that converged on the same shape, and the one that wrote down most plainly what the assembly actually cost.
The standard workaround put a human in the loop, not to make decisions but to relay messages. Brex's verdict: "That's an expensive solution to a plumbing problem." This is the same per-task isolation argument made in one environment per task, and the loop closure is the subject of feedback loops.