[DynamicIO] Cache not purged in latest Canary when deployed to Vercel

[mordechaim]

Link to the code that reproduces this issue

https://github.com/mordechaim/vercel-deploy-cache

To Reproduce

1. Visit https://vercel-deploy-cache.vercel.app/
2. Change the number field
3. Watch the optimistic value revert to its old value as network roundtrip returns

Current vs. Expected behavior

I expect expireTag to purge the cache and the number to update, but it keeps loading a stale cached value.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Home
  Available memory (MB): 32674
  Available CPU cores: 8
Binaries:
  Node: 22.9.0
  npm: 10.9.0
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.1.1-canary.18 // Latest available version is detected (15.1.1-canary.18).
  eslint-config-next: N/A
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

dynamicIO

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

Vercel (Deployed)

Additional context

This works perfectly on local dev/build/start, it's only present when deployed on Vercel. It is a recent regression, as it worked perfectly on [email protected]. I did not run a bisect to observe which version broke it.