test(hygiene): close every brain the remaining suites create

id-normalization.test.ts's makeBrain() and degraded-reads-surfaced.test.ts's
per-test brains had nothing tracking them — both now use a describe-scoped
opened[] array drained by afterEach.

find-hybrid-filter-before-hydrate.test.ts had two beforeAll-built brains
(one per describe block) with no matching afterAll.

multi-process-safety.test.ts and plugin-autodetect.test.ts/plugin.test.ts
left a brain whose init() was expected to reject (a rejected init() still
registers the instance in Brainy's global instance registry — the
constructor does that unconditionally — so it still needs close() to
deregister, or the process-level shutdown hooks never see the registry go
idle for the rest of the run).

tests/unit/brainy/degraded-reads-surfaced.test.ts

@@ -19,13 +19,19 @@ import { prodLog } from '../../../src/utils/logger.js'
 const UUID = (suffix: string): string => `00000000-0000-4000-8000-0000000000${suffix}`
 
 describe('Finding 10 — degraded derived-index state is surfaced on reads', () => {
+  const opened: Brainy[] = []
+
   beforeEach(() => {
     process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
   })
-  afterEach(() => vi.restoreAllMocks())
+  afterEach(async () => {
+    vi.restoreAllMocks()
+    for (const b of opened.splice(0)) await b.close().catch(() => {})
+  })
 
   it('checkHealth() reports adopt-forward degraded ids as unhealthy', async () => {
     const brain = new Brainy({ storage: { type: 'memory' }, dimensions: 384, requireSubtype: false })
+    opened.push(brain)
     await brain.init()
     ;(brain as any)._indexDegradedIds.add(UUID('de'))
 
@@ -37,6 +43,7 @@ describe('Finding 10 — degraded derived-index state is surfaced on reads', ()
   it('find()/get() warn loudly while degraded, ONCE, then repairIndex() clears it', async () => {
     const warn = vi.spyOn(prodLog, 'warn').mockImplementation(() => {})
     const brain = new Brainy({ storage: { type: 'memory' }, dimensions: 384, requireSubtype: false })
+    opened.push(brain)
     await brain.init()
     await brain.add({ id: UUID('a1'), data: 'x', type: NounType.Document })
     ;(brain as any)._indexRebuildFailed = new Error('rebuild boom')
@@ -59,6 +66,7 @@ describe('Finding 10 — degraded derived-index state is surfaced on reads', ()
 
   it('persistSingleOp records receipt.degraded (widened return type, not dropped)', async () => {
     const brain = new Brainy({ storage: { type: 'memory' }, dimensions: 384, requireSubtype: false })
+    opened.push(brain)
     await brain.init()
     // Simulate a degraded receipt by wrapping the generation store's commitSingleOp.
     const gs: any = (brain as any).generationStore