chore(ci): stop windows-latest/Node-24 vitest worker OOM kills

Recent main runs failed only on the windows-latest + Node 24 matrix cell:
~5 forks-pool workers died with "Worker exited unexpectedly" (an OS reap, no
JS error — classic OOM), which (a) surfaced as unhandled errors and (b)
dropped packages/mcp-server/src/profiles.js function coverage from 87.5% to
83.33%, under its 85% per-file floor. It reproduced on neither ubuntu nor
windows/Node-22, nor locally (test:coverage passes clean: 1172 tests,
profiles.js funcs 87.5%, zero crashes).

Root cause: NODE_OPTIONS=--max-old-space-size=4096 was set at the workflow
env level (for the tsup/tsc build) and inherited by the vitest test step, so
every forked worker was allowed a 4GB heap; several parallel workers ×4GB on
the Node-24 Windows runner caused OOM worker kills.

Fix (CI-only, no package change):
- Move NODE_OPTIONS=--max-old-space-size=4096 off the global env onto the
  build and typecheck steps only; the multi-worker test step now runs with
  Node's default per-worker heap.
- Cap the vitest forks pool to maxForks=2 in CI (poolOptions.forks) to bound
  peak concurrent memory. Local runs keep default parallelism.

Verified the config parses and tests pass under CI=1 locally (maxForks path);
the OOM kills only repro on the hosted runner, so the real confirmation is the
next CI run on this commit.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: A.R.

.github/workflows/ci.yml

@@ -7,10 +7,14 @@ on:
 
 env:
   PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: "1"
-  # tsup's --dts worker hits Node's default ~2GB heap during the mcp-server
-  # build (70+ entry points + DTS emission). Lift the cap to 4GB; both
-  # ubuntu-latest and windows-latest runners have ~7GB RAM available.
-  NODE_OPTIONS: "--max-old-space-size=4096"
+  # NOTE: NODE_OPTIONS=--max-old-space-size is deliberately NOT set at the
+  # workflow level. The vitest `forks` pool spawns several worker child
+  # processes that inherit this env; a 4GB-per-worker cap let the
+  # windows-latest + Node 24 runner OOM-kill workers ("Worker exited
+  # unexpectedly"), which failed the run AND dropped per-file coverage below
+  # threshold (issue: Windows CI flakiness). The heap bump is scoped to the
+  # build/typecheck steps only — see below; the test step runs with Node's
+  # default per-worker heap.
   # Opt into Node 24 for GitHub-shipped JS actions (checkout, setup-node, …)
   # ahead of the June 2nd 2026 default. Silences the deprecation warning and
   # ensures we're on the runtime GitHub is migrating to.
@@ -47,8 +51,16 @@ jobs:
           elif [ "$RUNNER_OS" = "macOS" ]; then
             npm install --no-save --workspaces=false @tailwindcss/oxide-darwin-arm64 @tailwindcss/oxide-darwin-x64
           fi
+      # tsup's --dts worker + tsc across 4 packages can exceed Node's default
+      # heap on the mcp-server build (70+ entry points + DTS emission). Lift the
+      # cap to 4GB for these single-process steps ONLY — never the multi-worker
+      # test step (see env note above).
       - run: npm run build
+        env:
+          NODE_OPTIONS: "--max-old-space-size=4096"
       - run: npm run typecheck
+        env:
+          NODE_OPTIONS: "--max-old-space-size=4096"
       - name: Test with coverage
         run: |
           mkdir -p .test-artifacts

vitest.config.ts

@@ -25,6 +25,16 @@ export default defineConfig({
         : []),
     ],
     environment: "node",
+    // CI (notably windows-latest + Node 24) intermittently OOM-killed
+    // forks-pool workers ("Worker exited unexpectedly"), which both failed the
+    // run and dropped per-file coverage below threshold. Cap concurrent forks
+    // in CI to bound peak memory (combined with not inheriting a 4GB-per-worker
+    // heap — see .github/workflows/ci.yml). Local runs keep vitest's default
+    // parallelism for speed.
+    pool: "forks",
+    ...(process.env.CI
+      ? { poolOptions: { forks: { maxForks: 2, minForks: 1 } } }
+      : {}),
     coverage: {
       provider: "v8",
       reporter: ["text", "html", "json-summary"],