Link to the code that reproduces this issue

https://github.com/1b0t/nextjs-custom-cache-handler-bug

To Reproduce

When implementing a custom CacheHandler in Next.js and the set method is called for a full page cache (e.g., /index), the tags property within the ctx argument appears to be missing. This occurs even when fetch requests with the next: { tags: [...] } option are present within the page component's rendering tree.

This behavior is unexpected, as the documentation suggests that tags associated with fetch requests during the rendering process should be available to the cache handler for invalidation purposes. The absence of these tags in the ctx for full page caches prevents custom cache handlers from effectively leveraging tag-based revalidation strategies for entire pages.

While a minimal reproduction repository would be ideal, here's a general outline of how to observe this issue:

1. Implement a custom CacheHandler in your next.config.js file.

2. Within a page component (e.g., pages/index.js or app/page.js), make one or more fetch requests with the next: { tags: [...] } option. For example:

   // app/page.tsx (or similar in app directory)
   async function getData() {
     const res = await fetch('/api/data', { 
       cache: 'force-cache',
       next: { tags: ['my-data-tag', 'home-page'] },
     });
     // ...
   }
   
   export default async function Home() {
     const data = await getData();
     // ...
     return <div>{/* ... */}</div>;
   }

3. In your custom CacheHandler's set method, log or inspect the ctx argument when the key corresponds to a full page cache (e.g., the key might resemble the route path or a hash thereof).

   // cache-handler.js
   const myCacheHandler = {
     async get(key, ctx) {
       // ... your get logic
     },
     async set(key, value, ctx) {
       console.log('Cache SET context for key:', key, ctx); // Observe the ctx object
       // ... your set logic
     },
     async revalidateTag(tag, ctx) {
       // ... your revalidateTag logic
     },
   };

   // next.config.js
   module.exports = {
     cacheHandler: require.resolve('./cache-handler.js'),
     cacheMaxMemorySize: 0, // disable default in-memory caching
   }

4. Build and run your Next.js application in a production-like environment (using next build and next start).

5. Access the page (e.g., /). Observe the logs from your custom CacheHandler's set method. You will likely find that the tags property in the ctx is missing or undefined for the full page cache entry, even though the fetch request within the page had tags.

Current vs. Expected behavior

Expected Behavior:

The ctx argument in the set method of a custom CacheHandler for full page caches should include the tags associated with any fetch requests made with the next: { tags: [...] } option during the server-side rendering or Server Components rendering of that page. This would allow custom cache handlers to store and utilize these tags for future revalidation.

Current Behavior:

The tags property in the ctx argument of the set method is missing (or undefined) for full page cache entries, despite the presence of tagged fetch requests in the page component tree.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:47 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6030
  Available memory (MB): 36864
  Available CPU cores: 12
Binaries:
  Node: 22.15.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 9.15.2
Relevant Packages:
  next: 15.4.0-canary.23 // Latest available version is detected (15.4.0-canary.23).
  eslint-config-next: 15.3.0
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.7.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Not sure

Which stage(s) are affected? (Select all that apply)

next start (local)

Additional context

Operating System:
Platform: darwin
Arch: arm64
Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:47 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6030
Available memory (MB): 36864
Available CPU cores: 12
Binaries:
Node: 22.15.0
npm: 10.9.2
Yarn: 1.22.22
pnpm: N/A
Relevant Packages:
next: 15.4.0-canary.23 // Latest available version is detected (15.4.0-canary.23).
eslint-config-next: 15.3.1
react: 19.1.0
react-dom: 19.1.0
typescript: 5.8.3
Next.js Config:
output: N/A