test(driver-sqlite-wasm): run the persistence suites' temp files on /dev/shm, so a flush's fsync stops waiting on the shard's other suites

packages/drivers/driver-sqlite-wasm/vitest.config.ts

@@ -1,4 +1,56 @@
 // Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
 
-// This package needs nothing beyond the shared preset; see its header.
-export { default } from '../../../vitest.preset.mts';
+import { accessSync, constants } from 'node:fs';
+import { defineConfig } from 'vitest/config';
+
+// This package re-exported the shared preset until #27076. It now carries one
+// key of its own, `test.env.TMPDIR`, so the preset's one setting is restated
+// below (a merged or wrapped preset is not what
+// scripts/check-console-intercept-disarm.mjs judges in a config's place).
+// Every other key stays on vitest's defaults (`globals: false`,
+// `environment: 'node'`), exactly as under the bare re-export.
+//
+// ## Why TMPDIR points at a memory-backed directory
+//
+// The persistence tests write a real database file under `os.tmpdir()`, and
+// every flush ends in `atomicWriteFile`'s `handle.sync()` (fsync before the
+// rename; see wasm-connection.ts). An fsync waits for the disk's queue, and on
+// a Test Core shard that queue belongs to the other suites sharing the runner.
+// Measured (#27076): `should persist data on-write` takes about 30 ms on an
+// idle disk and 5,026 ms on schedule run 40654333991 (Test Core 6/8), where it
+// timed out; run 39853791549 timed out five on-write and flush cases the same
+// way. Locally, with four `dd … conv=fsync` writers on the same disk, those
+// cases took 1.4–3.6 s; with TMPDIR on /dev/shm under the same writers, every
+// case in the four persistence files stayed under 0.6 s.
+//
+// So the cases' wall time measured the neighbours' disk, not the driver. On a
+// tmpfs the same code still runs, `sync()` included: what each case asserts
+// (bytes on disk, atomic rename, the flush chain, the failure report) is
+// unchanged; only the wait for unrelated I/O is gone. Budgets, fixtures and
+// cases are untouched.
+//
+// A host without a writable /dev/shm (macOS, Windows) keeps its own temp
+// directory: the setting is absent there, not an error.
+const MEMORY_BACKED_TMP = '/dev/shm';
+
+function writableDir(dir: string): boolean {
+  try {
+    accessSync(dir, constants.W_OK);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export default defineConfig({
+  test: {
+    // A late console.* must not redden a green suite (#10374): vitest's worker
+    // forwards console output over RPC and discards the promise, and a write
+    // landing after teardown's rpcDone() snapshot is rejected into an unhandled
+    // error — a fully green run that exits 1. Disarming removes the mechanism.
+    // Mechanism + measured costs: examples/app-showcase/vitest.config.ts.
+    // Enforced repo-wide by scripts/check-console-intercept-disarm.mjs.
+    disableConsoleIntercept: true,
+    env: writableDir(MEMORY_BACKED_TMP) ? { TMPDIR: MEMORY_BACKED_TMP } : {},
+  },
+});