fix(monitoring): cache payload instance in logger to prevent flaky tests

The fire-and-forget dynamic import chain (3 awaits) was racing with
test flush timeouts. Caching the resolved payload instance fixes both
the flakiness and eliminates per-call import overhead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/monitoring/monitoring-logger.ts

@@ -39,6 +39,22 @@ export interface MonitoringLoggerInstance {
   fatal(message: string, context?: LogContext): void
 }
 
+/** Cached Payload instance — resolved once, reused for all subsequent writes. */
+let cachedPayload: { create: (...args: unknown[]) => Promise<unknown> } | null = null
+
+async function getPayloadInstance() {
+  if (cachedPayload) return cachedPayload
+  const { getPayload } = await import('payload')
+  const config = (await import(/* @vite-ignore */ '@payload-config')).default
+  cachedPayload = await getPayload({ config })
+  return cachedPayload
+}
+
+/** Reset cached instance (used in tests). */
+export function _resetPayloadCache(): void {
+  cachedPayload = null
+}
+
 async function writeLog(
   source: LogSource,
   level: LogLevel,
@@ -48,9 +64,7 @@ async function writeLog(
   if (!shouldLog(level)) return
 
   try {
-    const { getPayload } = await import('payload')
-    const config = (await import('@payload-config')).default
-    const payload = await getPayload({ config })
+    const payload = await getPayloadInstance()
 
     const { requestId, userId, tenant, duration, ...rest } = context || {}
 
@@ -69,6 +83,7 @@ async function writeLog(
     })
   } catch {
     // Fallback to console if Payload is not yet initialized
+    cachedPayload = null
     const prefix = `[${source}][${level.toUpperCase()}]`
     console.log(prefix, message, context || '')
   }

tests/unit/monitoring/monitoring-logger.unit.spec.ts

@@ -11,16 +11,17 @@ vi.mock('@payload-config', () => ({
   default: {},
 }))
 
-import { createMonitoringLogger } from '@/lib/monitoring/monitoring-logger'
+import { createMonitoringLogger, _resetPayloadCache } from '@/lib/monitoring/monitoring-logger'
 
 /** Wait long enough for fire-and-forget promises to settle. */
 async function flush(): Promise<void> {
-  await new Promise((resolve) => setTimeout(resolve, 50))
+  await new Promise((resolve) => setTimeout(resolve, 150))
 }
 
 describe('MonitoringLogger', () => {
   beforeEach(() => {
     vi.clearAllMocks()
+    _resetPayloadCache()
     mockGetPayload.mockResolvedValue({ create: mockCreate })
     mockCreate.mockResolvedValue({ id: '1' })
     delete process.env.MONITORING_LOG_LEVEL