A few weeks ago we taught the build executor to run independent subtasks in
parallel, across multiple LLM providers at once. That work was about throughput,
and it worked. But it left a blind spot: when a build finished, the cost and the timing came back as a single
aggregate. Total tokens. Total dollars. Total wall-clock. Useful, but it couldn't
answer the question you actually ask after a parallel run: which worker spent
that money, on which provider, in which model, and where did the time go?
This session was about closing that gap. The headline is per-worker
observability. The theme is that all of it is additive — the parallel build
spine didn't change, we just put instruments on it. The same session also carried
a GitHub Actions security pass and a god-file decomposition, because they were
sitting in the same backlog and they unblock the work above.