[reaperhulk]

The Static checks job took 42 s on the last merge-queue run (41004903518): 18 s checking out the repository, then 20.6 s running its 15 checks one after another. Their CPU time is about 33 s, which spread over the runner's four cores is about 8 s.

Change

• Each check is now a background: true step, and a wait-all: step at the end fails the job if any of them failed. Each check keeps its own step and log.
• At most 10 background steps run at once and the rest queue, so the steps are listed slowest first:
  • run_unit_tests.py
  • check_lean_speed.py
  • check_variants.py
  • check_lean_imports.py
  • check_mcdt.py
  • …the quick checks last.

The checkout stays as it was. A sparse checkout that left out vectors/ made it slower: 25 s instead of 18 s, because it fetches each of this job's 27,000 files on demand.

Result

On this PR's run (41011468451), the job took 34 s instead of 42 s:

	Before	After
Checks, start to finish	20.6 s	13 s
Checkout	18 s	17 s

A step's own time now includes waiting for a core while the others run. For example, check_arch_gates.py shows 9 s instead of 0 s, so judge the change by the job's total time, not by single steps.

Testing

• Every check and all-green passed in this PR's run.
• Only ci.yml changes.

🤖 Generated with Claude Code

https://claude.ai/code/session_015ajQWwSSE6PJMaZ9NzWaSV