Tests: cap Vitest workers on CI macOS

scripts/test-parallel.mjs

@@ -22,13 +22,15 @@ const parallelRuns = runs.filter((entry) => entry.name !== "gateway");
 const serialRuns = runs.filter((entry) => entry.name === "gateway");
 
 const children = new Set();
+const isCI = process.env.CI === "true" || process.env.GITHUB_ACTIONS === "true";
+const isMacOS = process.platform === "darwin" || process.env.RUNNER_OS === "macOS";
 const overrideWorkers = Number.parseInt(process.env.CLAWDBOT_TEST_WORKERS ?? "", 10);
 const resolvedOverride = Number.isFinite(overrideWorkers) && overrideWorkers > 0 ? overrideWorkers : null;
 const localWorkers = Math.max(4, Math.min(16, os.cpus().length));
 const perRunWorkers = Math.max(1, Math.floor(localWorkers / parallelRuns.length));
-// Keep worker counts predictable across local runs and CI (avoid oversubscribing runners).
-// Total workers ~= localWorkers since we run unit/extensions in parallel.
-const maxWorkers = resolvedOverride ?? perRunWorkers;
+// Keep worker counts predictable for local runs and for CI on macOS.
+// In CI on linux/windows, prefer Vitest defaults to avoid cross-test interference from lower worker counts.
+const maxWorkers = resolvedOverride ?? (isCI && !isMacOS ? null : perRunWorkers);
 
 const WARNING_SUPPRESSION_FLAGS = [
   "--disable-warning=ExperimentalWarning",