The singleton/global-state bucket was the only bucket left unchunked, and
it is the one that got OOM-killed: 79 files in a single `bun test`
process exited 137. Chunking exists precisely to hold peak RSS under the
runner's ceiling, so the bucket that opts out is the bucket that hits it.
The stated reason for leaving it whole does not hold. That bucket is
selected because its suites mutate process-wide state, and what keeps
them from colliding is sequencing, which `parallel: 1` already
guarantees. Splitting them across processes strictly increases isolation
rather than reducing it. Use 10 files per chunk, the width the 650-file
native bucket already sustains on the same runner.
Separately, the sequential path could not say why a chunk was SIGKILLed.
It arms a watchdog but never records when the watchdog fires, so an OOM
kill and a watchdog kill both surfaced as a bare "failed with exit code
137" - the exact message this failure produced, which points at neither
remedy. The parallel path already tracks this; apply the same idea here
and name the cause.
Muhammad Mustaqeem
6b78c4e112