Reviewer noted `--max-concurrency=1` was applied to both buckets. Slow
bucket needs it (subprocesses, ports, shared state → flaky in parallel)
but fast bucket was unnecessarily capped. Remove the flag for fast;
keep for slow.
Verified: test:fast still green (2510 pass, 14.4s locally).
Reviewer flagged that the manual `slowTests` array silently degrades
`test:fast` if new subprocess/server/timer tests are added without being
declared slow (no literal `dist/` means auto-detection misses them).
Interim fix: explicit 5-rule criteria block in the script so contributors
know when to add a test.
Enforcement (automated perf-budget warning in push-ci.yml) tracked in
issue #1071.
Tam Nhu Tran