[gmpassos]

Summary

• Each test_chrome shard runs its test files 4 at a time (TEST_CONCURRENCY), instead of one at a time (ci: test files in parallel; one Chrome job per compiler #61).
• One at a time was needed because parallel test files lost coverage (lines run by async work after a file's last test) and timing tests flaked. Since 3.1.8 (feat(UIRoot): close() awaits a real shutdown; test roots close after their tests; 3.1.8 #62) a test root waits until idle and shuts down after its tests, which should fix both.

Test plan

• CI green (the timing tests included).
• Coverage equals master's (codecov/project, no lines lost).
• Wall time compared with master's ~3 min.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.68%. Comparing base (68e5ba5) to head (95f44e7).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #63      +/-   ##
==========================================
- Coverage   93.05%   92.68%   -0.38%     
==========================================
  Files          34       34              
  Lines        9537     9537              
==========================================
- Hits         8875     8839      -36     
- Misses        662      698      +36     

Flag	Coverage Δ
unittests	92.68% <ø> (-0.38%)	⬇️

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[gmpassos]

Closing without merging: running 4 test files at once per shard passed every test and cut CI to ~1m49s, but coverage dropped 36 lines (93.05% → 92.68%). The lost lines include synchronous code from tests that ran, which points to package:test's shared-tab Chrome coverage collection (Profiler.takePreciseCoverage per suite) rather than late async work. Browser test shards stay at one file at a time (#61).