Deflake TestWorkflowEngine_ParallelExecution

[ChrisJBurns]

Summary

TestWorkflowEngine_ParallelExecution failed the unit-test job on main (e.g. commit 2858ac8c3) with:

workflow_engine_test.go:531: "1" is not greater than or equal to "2"
Messages: at least 2 steps should run concurrently

Why: The test proves the two independent level-1 steps run in parallel by asserting maxConcurrent >= 2. That counter only reaches 2 if the two 50ms mock sleeps overlap in wall-clock time. On a loaded CI runner the second goroutine can be starved and start only after the first has already finished its sleep, leaving maxConcurrent == 1 — so the test fails regardless of the change under test. The failure is unrelated to the commit it landed on (that PR does not touch pkg/vmcp/composer). This test was previously "deflaked" in #4333, which reduced but did not remove the timing dependence.

What: Replaces the sleeps with a rendezvous barrier — each fetch step blocks on entry until both have arrived, so neither can complete until the other has started. The concurrency assertion is now deterministic under any scheduler load. As a bonus, a genuine regression to sequential execution now surfaces as a clear timeout failure instead of a lucky pass. The engine already runs level steps in parallel via errgroup + a size-10 semaphore, so a barrier of 2 is always satisfiable.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Test plan

• Ran go test ./pkg/vmcp/composer/ -run TestWorkflowEngine_ParallelExecution -race -count=30 — all pass, no races.
• Ran the full pkg/vmcp/composer package with -race — green.

Does this introduce a user-facing change?

No.

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.42%. Comparing base (9ce78fa) to head (3a55f41).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6112      +/-   ##
==========================================
- Coverage   72.43%   72.42%   -0.02%     
==========================================
  Files         734      733       -1     
  Lines       75871    75833      -38     
==========================================
- Hits        54960    54924      -36     
+ Misses      17019    17014       -5     
- Partials     3892     3895       +3     

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