diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1b0577fe32b..c8024bc4401 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,8 @@
 
 ### Server
 - Enhance: リモートノートクリーニングジョブのスキップ処理のパフォーマンス改善
+- Fix: backend バンドルで `@tensorflow/tfjs-node` を external に含めず、起動時に `@mapbox/node-pre-gyp` の `find()` が backend の package.json を誤検出して `is not node-pre-gyp ready` エラーを永続的に吐く問題を修正
+- Fix: MemoryKVCacheのキャッシュGC処理において、更新されたキャッシュが期限切れにならないことがある問題を修正
 - Fix: PerUserDriveChart がシステム所有ファイル (userId が null) の更新で `"group"` の非NULL制約違反によりクラッシュする問題を修正 (#17498)
 - Enhance: リモートノートクリーニングジョブの削除対象検索処理のパフォーマンス改善
 - Fix: センシティブメディア自動検出周りの依存関係・ファイルの解決に失敗する問題を修正
diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
index f9692ce5d5f..f1eae582a89 100644
--- a/packages/backend/src/misc/cache.ts
+++ b/packages/backend/src/misc/cache.ts
@@ -299,12 +299,8 @@ export class MemoryKVCache<T> {
 		const now = Date.now();
 
 		for (const [key, { date }] of this.cache.entries()) {
-			// The map is ordered from oldest to youngest.
-			// We can stop once we find an entry that's still active, because all following entries must *also* be active.
 			const age = now - date;
-			if (age < this.lifetime) break;
-
-			this.cache.delete(key);
+			if (age >= this.lifetime) this.cache.delete(key);
 		}
 	}
 
diff --git a/packages/backend/test/unit/misc/cache.ts b/packages/backend/test/unit/misc/cache.ts
new file mode 100644
index 00000000000..297378304e2
--- /dev/null
+++ b/packages/backend/test/unit/misc/cache.ts
@@ -0,0 +1,234 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+import { MemoryKVCache, MemorySingleCache } from '@/misc/cache.js';
+
+describe('misc:MemoryKVCache', () => {
+	beforeEach(() => {
+		vi.useFakeTimers();
+	});
+
+	afterEach(() => {
+		vi.useRealTimers();
+	});
+
+	test('set and get returns the value within lifetime', () => {
+		const cache = new MemoryKVCache<string>(1000);
+		cache.set('key', 'value');
+		expect(cache.get('key')).toBe('value');
+		cache.dispose();
+	});
+
+	test('get returns undefined after lifetime expires', () => {
+		const cache = new MemoryKVCache<string>(1000);
+		cache.set('key', 'value');
+		vi.advanceTimersByTime(1001);
+		expect(cache.get('key')).toBeUndefined();
+		cache.dispose();
+	});
+
+	test('delete removes the entry', () => {
+		const cache = new MemoryKVCache<string>(1000);
+		cache.set('key', 'value');
+		cache.delete('key');
+		expect(cache.get('key')).toBeUndefined();
+		cache.dispose();
+	});
+
+	describe('gc()', () => {
+		test('removes expired entries', () => {
+			const cache = new MemoryKVCache<string>(1000);
+			cache.set('a', '1');
+			cache.set('b', '2');
+			vi.advanceTimersByTime(1001);
+			cache.gc();
+			expect(cache.get('a')).toBeUndefined();
+			expect(cache.get('b')).toBeUndefined();
+			cache.dispose();
+		});
+
+		test('retains entries that have not yet expired', () => {
+			const cache = new MemoryKVCache<string>(2000);
+			cache.set('a', '1');
+			vi.advanceTimersByTime(1001);
+			cache.gc();
+			expect(cache.get('a')).toBe('1');
+			cache.dispose();
+		});
+
+		test('removes only expired entries when mixed with live entries', () => {
+			const cache = new MemoryKVCache<string>(2000);
+			cache.set('old', 'oldValue');
+			vi.advanceTimersByTime(2001);
+			cache.set('new', 'newValue');
+			cache.gc();
+			expect(cache.get('old')).toBeUndefined();
+			expect(cache.get('new')).toBe('newValue');
+			cache.dispose();
+		});
+
+		// Regression test for https://github.com/misskey-dev/misskey/issues/15500
+		// Updated keys keep their original insertion position in Map. gc() must not
+		// assume that entries are ordered from oldest to youngest, otherwise it can
+		// stop early at an updated key and leave later, truly-expired keys alive.
+		// The key observable symptom is that gc() fails to *remove* the expired entry
+		// from the Map — get() has its own expiry check so it returns undefined either
+		// way, but the stale entry keeps consuming memory.
+		test('correctly expires old entries after a key is updated (issue #15500)', () => {
+			const lifetime = 1000;
+			const cache = new MemoryKVCache<string>(lifetime);
+
+			// Insert 'a' and 'b' at t=0
+			cache.set('a', 'v1');
+			cache.set('b', 'v1');
+
+			// Advance time and update 'a'. It stays at position 0 in the Map, so a
+			// gc() implementation that stops at the first fresh entry would leave 'b'
+			// in the Map even though get() would hide it as expired.
+			vi.advanceTimersByTime(500);
+			cache.set('a', 'v2'); // refresh 'a'; 'b' is still at t=0
+
+			// 'b' is now expired, 'a' has 400ms left
+			vi.advanceTimersByTime(600); // total 1100ms
+
+			cache.gc();
+
+			// Verify the entry is actually removed from the Map, not just hidden by get().
+			// get() always checks expiry itself, so it returns undefined even without gc() —
+			// the real bug is memory not being freed.
+			const entries = [...cache.entries];
+			expect(entries.find(([k]) => k === 'b')).toBeUndefined(); // 'b' must be gone from Map
+			expect(entries.find(([k]) => k === 'a')?.[1].value).toBe('v2'); // 'a' still in Map
+			cache.dispose();
+		});
+
+		test('gc does not break when cache is empty', () => {
+			const cache = new MemoryKVCache<string>(1000);
+			expect(() => cache.gc()).not.toThrow();
+			cache.dispose();
+		});
+	});
+
+	test('set does not cause active entries iteration to revisit the same key', () => {
+		const cache = new MemoryKVCache<{ id: string }>(1000);
+		cache.set('key', { id: 'user-1' });
+
+		let iterations = 0;
+		for (const [key, { value }] of cache.entries) {
+			iterations++;
+			if (value.id === 'user-1') {
+				cache.set(key, value);
+			}
+
+			expect(iterations).toBeLessThan(3);
+		}
+
+		expect(iterations).toBe(1);
+		cache.dispose();
+	});
+
+	describe('fetch()', () => {
+		test('calls fetcher on cache miss', async () => {
+			const cache = new MemoryKVCache<string>(1000);
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch('key', fetcher);
+			expect(fetcher).toHaveBeenCalledOnce();
+			expect(result).toBe('fetched');
+			cache.dispose();
+		});
+
+		test('does not call fetcher on cache hit', async () => {
+			const cache = new MemoryKVCache<string>(1000);
+			cache.set('key', 'cached');
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch('key', fetcher);
+			expect(fetcher).not.toHaveBeenCalled();
+			expect(result).toBe('cached');
+			cache.dispose();
+		});
+
+		test('respects validator and bypasses cache when validator returns false', async () => {
+			const cache = new MemoryKVCache<string>(1000);
+			cache.set('key', 'cached');
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch('key', fetcher, () => false);
+			expect(fetcher).toHaveBeenCalledOnce();
+			expect(result).toBe('fetched');
+			cache.dispose();
+		});
+	});
+
+	describe('fetchMaybe()', () => {
+		test('does not cache undefined returned by fetcher', async () => {
+			const cache = new MemoryKVCache<string>(1000);
+			const fetcher = vi.fn().mockResolvedValue(undefined);
+			const result = await cache.fetchMaybe('key', fetcher);
+			expect(result).toBeUndefined();
+			// A second call should invoke the fetcher again because undefined was not cached
+			await cache.fetchMaybe('key', fetcher);
+			expect(fetcher).toHaveBeenCalledTimes(2);
+			cache.dispose();
+		});
+	});
+});
+
+describe('misc:MemorySingleCache', () => {
+	beforeEach(() => {
+		vi.useFakeTimers();
+	});
+
+	afterEach(() => {
+		vi.useRealTimers();
+	});
+
+	test('set and get returns the value within lifetime', () => {
+		const cache = new MemorySingleCache<string>(1000);
+		cache.set('value');
+		expect(cache.get()).toBe('value');
+	});
+
+	test('get returns undefined after lifetime expires', () => {
+		const cache = new MemorySingleCache<string>(1000);
+		cache.set('value');
+		vi.advanceTimersByTime(1001);
+		expect(cache.get()).toBeUndefined();
+	});
+
+	test('delete removes the cached value', () => {
+		const cache = new MemorySingleCache<string>(1000);
+		cache.set('value');
+		cache.delete();
+		expect(cache.get()).toBeUndefined();
+	});
+
+	describe('fetch()', () => {
+		test('calls fetcher on cache miss', async () => {
+			const cache = new MemorySingleCache<string>(1000);
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch(fetcher);
+			expect(fetcher).toHaveBeenCalledOnce();
+			expect(result).toBe('fetched');
+		});
+
+		test('does not call fetcher on cache hit', async () => {
+			const cache = new MemorySingleCache<string>(1000);
+			cache.set('cached');
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch(fetcher);
+			expect(fetcher).not.toHaveBeenCalled();
+			expect(result).toBe('cached');
+		});
+
+		test('respects validator and bypasses cache when validator returns false', async () => {
+			const cache = new MemorySingleCache<string>(1000);
+			cache.set('cached');
+			const fetcher = vi.fn().mockResolvedValue('fetched');
+			const result = await cache.fetch(fetcher, () => false);
+			expect(fetcher).toHaveBeenCalledOnce();
+			expect(result).toBe('fetched');
+		});
+	});
+});