diff --git a/src/Utils/auth-utils.ts b/src/Utils/auth-utils.ts
index 67ee65f409d..69196c1cba4 100644
Binary files a/src/Utils/auth-utils.ts and b/src/Utils/auth-utils.ts differ
diff --git a/src/__tests__/Utils/auth-utils.cross-store-isolation.test.ts b/src/__tests__/Utils/auth-utils.cross-store-isolation.test.ts
new file mode 100644
index 00000000000..6759df56b1e
--- /dev/null
+++ b/src/__tests__/Utils/auth-utils.cross-store-isolation.test.ts
@@ -0,0 +1,96 @@
+/**
+ * Cross-store isolation of the shared AsyncLocalStorage.
+ *
+ * The transaction context storage is a single process-wide AsyncLocalStorage
+ * (the heap-leak fix — a per-socket instance leaks under Node's legacy
+ * async-context propagation). Because the instance is shared, its value is
+ * keyed by a per-store token so a wrapped store only ever resolves its own
+ * context, even when a second wrapped store runs inside the first store's
+ * transaction callback.
+ *
+ * Regression guard for: store B running inside store A's transaction seeing
+ * A's ambient context and committing B's writes into A's backing store.
+ */
+import type { SignalDataSet, SignalKeyStore } from '../../Types'
+import { addTransactionCapability } from '../../Utils/auth-utils'
+import type { ILogger } from '../../Utils/logger'
+
+const silentLogger = (): ILogger =>
+	({
+		level: 'silent',
+		child: () => silentLogger(),
+		trace: () => {},
+		debug: () => {},
+		info: () => {},
+		warn: () => {},
+		error: () => {},
+		fatal: () => {}
+	}) as unknown as ILogger
+
+const makeInMemoryStore = (): SignalKeyStore => {
+	const data: Record<string, Record<string, unknown>> = {}
+	return {
+		async get(type, ids) {
+			const bucket = data[type] ?? {}
+			const out: Record<string, any> = {}
+			for (const id of ids) {
+				if (id in bucket) out[id] = bucket[id]
+			}
+
+			return out
+		},
+		async set(d: SignalDataSet) {
+			for (const type in d) {
+				data[type] = data[type] ?? {}
+				const bucket = data[type]
+				const incoming = (d as any)[type] as Record<string, unknown>
+				for (const id in incoming) {
+					const v = incoming[id]
+					if (v === null) delete bucket[id]
+					else bucket[id] = v
+				}
+			}
+		}
+	}
+}
+
+const opts = { maxCommitRetries: 1, delayBetweenTriesMs: 1 }
+
+describe('addTransactionCapability — cross-store isolation', () => {
+	it('does not leak a transaction context into another store in the same async chain', async () => {
+		const backingA = makeInMemoryStore()
+		const backingB = makeInMemoryStore()
+		const a = addTransactionCapability(backingA, silentLogger(), opts)
+		const b = addTransactionCapability(backingB, silentLogger(), opts)
+
+		await a.transaction(async () => {
+			// b is untouched by a's ambient context
+			expect(b.isInTransaction()).toBe(false)
+			await b.set({ 'app-state-sync-key': { '1': { keyId: 9 } } } as never)
+			await a.set({ 'app-state-sync-key': { '1': { keyId: 1 } } } as never)
+		}, 'app-state-sync-key')
+
+		// b's write went straight to its own backing store, not into a's mutations
+		expect((await backingB.get('app-state-sync-key', ['1']))['1']).toMatchObject({ keyId: 9 })
+		expect((await backingA.get('app-state-sync-key', ['1']))['1']).toMatchObject({ keyId: 1 })
+	})
+
+	it('keeps nested transactions across stores isolated by token', async () => {
+		const backingA = makeInMemoryStore()
+		const backingB = makeInMemoryStore()
+		const a = addTransactionCapability(backingA, silentLogger(), opts)
+		const b = addTransactionCapability(backingB, silentLogger(), opts)
+
+		await a.transaction(async () => {
+			await a.set({ 'app-state-sync-key': { '1': { keyId: 1 } } } as never)
+			await b.transaction(async () => {
+				expect(a.isInTransaction()).toBe(true)
+				expect(b.isInTransaction()).toBe(true)
+				await b.set({ 'app-state-sync-key': { '1': { keyId: 2 } } } as never)
+			}, 'app-state-sync-key')
+		}, 'app-state-sync-key')
+
+		expect((await backingA.get('app-state-sync-key', ['1']))['1']).toMatchObject({ keyId: 1 })
+		expect((await backingB.get('app-state-sync-key', ['1']))['1']).toMatchObject({ keyId: 2 })
+	})
+})