From e70227d5810a94af2ec084de35c91a6ac86bcf32 Mon Sep 17 00:00:00 2001
From: Tianyi Cui <53024+tianyicui@users.noreply.github.com>
Date: Mon, 6 Jul 2026 20:59:47 +0800
Subject: [PATCH] =?UTF-8?q?workflow:=20pin=20the=20spec=20engine's=20concu?=
 =?UTF-8?q?rrency=20=E2=80=94=20the=20auto=20default=20is=20one=20slot=20o?=
 =?UTF-8?q?n=20small=20CI=20runners?=
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The two tests that wait for two children IN FLIGHT (the pipeline
no-barrier test and the dropped-promise cancellation test) inherited the
engine's auto-resolved maxConcurrentAgents, which is
min(16, max(1, cores - 2)) — exactly 1 on the 2-core CI runner, so the
second child never started and vi.waitFor timed out. Reproduced locally
under taskset -c 0,1; the full spec passes there with the helper pinning
a fixed ceiling. Tests about the ceiling itself keep their explicit
overrides, and the auto-resolve arm stays covered by the
default-config provider tests.
---
 packages/workflow/workflow-vm/tests/workflow-vm.spec.ts | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/packages/workflow/workflow-vm/tests/workflow-vm.spec.ts b/packages/workflow/workflow-vm/tests/workflow-vm.spec.ts
index a4058303ea..ac037bdb04 100644
--- a/packages/workflow/workflow-vm/tests/workflow-vm.spec.ts
+++ b/packages/workflow/workflow-vm/tests/workflow-vm.spec.ts
@@ -97,7 +97,10 @@ async function setup(options?: SetupOptions) {
     options?.disposeDelayMs ?? 0,
   )
   ctx.subagents.registerProvider(provider)
-  await ctx.plugin(VmWorkflowEngine, { provider: 'stub', ...options?.config })
+  // A fixed concurrency ceiling: the auto-resolved default is machine-derived
+  // (cores - 2, floored at 1), so tests that expect N children in flight
+  // would wedge on small CI runners. Tests about the ceiling override it.
+  await ctx.plugin(VmWorkflowEngine, { provider: 'stub', maxConcurrentAgents: 8, ...options?.config })
   return { ctx, provider, parent: fakeParent() }
 }