From ab26e187d7a260ac57c1e9451fdd8bfb2fb59160 Mon Sep 17 00:00:00 2001
From: "vercel-gh-bot-3[bot]"
 <282332853+vercel-gh-bot-3[bot]@users.noreply.github.com>
Date: Fri, 24 Jul 2026 21:29:07 +0000
Subject: [PATCH 1/2] test: cover filesystem cache URL key accounting

---
 .../lib/router-utils/filesystem.test.ts       | 73 +++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 packages/next/src/server/lib/router-utils/filesystem.test.ts

diff --git a/packages/next/src/server/lib/router-utils/filesystem.test.ts b/packages/next/src/server/lib/router-utils/filesystem.test.ts
new file mode 100644
index 00000000000..39e6a5433a9
--- /dev/null
+++ b/packages/next/src/server/lib/router-utils/filesystem.test.ts
@@ -0,0 +1,73 @@
+import { mkdir, mkdtemp, rm, writeFile } from 'fs/promises'
+import { tmpdir } from 'os'
+import { join } from 'path'
+import { defaultConfig } from '../../config-shared'
+import { setupFsCheck } from './filesystem'
+
+describe('filesystem cache', () => {
+  let dir: string
+
+  beforeEach(async () => {
+    dir = await mkdtemp(join(tmpdir(), 'next-fs-check-'))
+    const distDir = join(dir, '.next')
+    const serverDir = join(distDir, 'server')
+    await mkdir(serverDir, { recursive: true })
+
+    await Promise.all([
+      writeFile(join(distDir, 'BUILD_ID'), 'build-id'),
+      writeFile(
+        join(distDir, 'routes-manifest.json'),
+        JSON.stringify({
+          redirects: [],
+          rewrites: { beforeFiles: [], afterFiles: [], fallback: [] },
+          headers: [],
+          onMatchHeaders: [],
+          dynamicRoutes: [],
+          dataRoutes: [],
+        })
+      ),
+      writeFile(
+        join(distDir, 'prerender-manifest.json'),
+        JSON.stringify({
+          preview: {
+            previewModeId: 'id',
+            previewModeSigningKey: 'signing-key',
+            previewModeEncryptionKey: 'encryption-key',
+          },
+        })
+      ),
+      writeFile(join(serverDir, 'pages-manifest.json'), '{}'),
+      writeFile(
+        join(serverDir, 'functions-config-manifest.json'),
+        JSON.stringify({ functions: {} })
+      ),
+    ])
+  })
+
+  afterEach(async () => {
+    await rm(dir, { recursive: true, force: true })
+  })
+
+  it('includes URL keys when limiting the production filesystem cache', async () => {
+    const fsChecker = await setupFsCheck({
+      dir,
+      dev: false,
+      config: { ...defaultConfig, output: 'standalone' },
+    })
+
+    fsChecker.pageFiles.add('/first')
+    expect(await fsChecker.getItem('/first')).toMatchObject({
+      itemPath: '/first',
+      type: 'pageFile',
+    })
+    fsChecker.pageFiles.delete('/first')
+
+    // The retained URL keys together exceed the cache's 1 MiB size limit.
+    const longSegment = 'x'.repeat(1024)
+    for (let index = 0; index < 1100; index++) {
+      await fsChecker.getItem(`/${longSegment}/${index}`)
+    }
+
+    expect(await fsChecker.getItem('/first')).toBeNull()
+  })
+})

From 1895c0d02e5a1a7893259c017e71b71b8be648fb Mon Sep 17 00:00:00 2001
From: "vercel-gh-bot-3[bot]"
 <282332853+vercel-gh-bot-3[bot]@users.noreply.github.com>
Date: Fri, 24 Jul 2026 21:38:37 +0000
Subject: [PATCH 2/2] fix: include keys in filesystem cache size

---
 packages/next/src/server/lib/lru-cache.ts               | 8 +++++---
 packages/next/src/server/lib/router-utils/filesystem.ts | 6 ++++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/packages/next/src/server/lib/lru-cache.ts b/packages/next/src/server/lib/lru-cache.ts
index 59b76b5d0b4..59c97293c0e 100644
--- a/packages/next/src/server/lib/lru-cache.ts
+++ b/packages/next/src/server/lib/lru-cache.ts
@@ -49,12 +49,14 @@ export class LRUCache<T> {
   private readonly tail: SentinelNode<T>
   private totalSize: number = 0
   private readonly maxSize: number
-  private readonly calculateSize: ((value: T) => number) | undefined
+  private readonly calculateSize:
+    | ((value: T, key: string) => number)
+    | undefined
   private readonly onEvict: ((key: string, value: T) => void) | undefined
 
   constructor(
     maxSize: number,
-    calculateSize?: (value: T) => number,
+    calculateSize?: (value: T, key: string) => number,
     onEvict?: (key: string, value: T) => void
   ) {
     this.maxSize = maxSize
@@ -124,7 +126,7 @@ export class LRUCache<T> {
    * - O(k) where k is the number of items evicted (can be O(N) for variable sizes)
    */
   public set(key: string, value: T): boolean {
-    const size = this.calculateSize?.(value) ?? 1
+    const size = this.calculateSize?.(value, key) ?? 1
     if (size <= 0) {
       throw new Error(
         `LRUCache: calculateSize returned ${size}, but size must be > 0. ` +
diff --git a/packages/next/src/server/lib/router-utils/filesystem.ts b/packages/next/src/server/lib/router-utils/filesystem.ts
index 6909eb2c773..eef4c50ef04 100644
--- a/packages/next/src/server/lib/router-utils/filesystem.ts
+++ b/packages/next/src/server/lib/router-utils/filesystem.ts
@@ -113,12 +113,14 @@ export async function setupFsCheck(opts: {
   config: NextConfigRuntime
 }) {
   const getItemsLru = !opts.dev
-    ? new LRUCache<FsOutput | null>(1024 * 1024, function length(value) {
+    ? new LRUCache<FsOutput | null>(1024 * 1024, function length(value, key) {
+        const keyLength = key.length
         if (!value) {
           // Null entries (negative cache) still need a non-zero size for LRU eviction
-          return 1
+          return keyLength || 1
         }
         return (
+          keyLength +
           (value.fsPath || '').length +
           value.itemPath.length +
           value.type.length