Add Below does not filter blocks with filterOptions

Describe the Bug

I recently implemented the filterOptions prop for a blocks field.

• the Add Content button at the end of the blocks already in the page launches the add blocks modal and correctly filters the available blocks

• the Add Below selection available on each block already in the page launches the add blocks modal and allows all blocks without applying the filter

Link to the code that reproduces this issue

https://github.com/tschwartz/payload-cms

Reproduction Steps

After cloning, installing and running dev. Observe that the last bullet of each is the difference between Expected and Observed.

Expected

1. Navigate to the admin panel: http://localhost:3000/admin
2. Add a page from the pages collection
3. Observe that the page has the default template selected
4. Click on Add content button
5. Observe there is only the ability to add RichText when the page has the default template selected
6. Click on RichText block
7. Observe that there is now a RichText block in the page content
8. Click on the triple dot of the RichText block
9. Click on the Add Below option
10. Observe there is only the ability to add RichText when the page has the default template selected

Observed

1. Navigate to the admin panel: http://localhost:3000/admin
2. Add a page from the pages collection
3. Observe that the page has the default template selected
4. Click on Add content button
5. Observe there is only the ability to add RichText when the page has the default template selected
6. Click on RichText block
7. Observe that there is now a RichText block in the page content
8. Click on the triple dot of the RichText block
9. Click on the Add Below option
10. Observe there is the ability to add RichText and Alert even when the page has the default template selected

Which area(s) are affected?

area: ui

Environment Info

This project is configured to use pnpm because /Users/tschwartz/dev/ea/tschwartz/payload-cms/package.json has a "packageManager" field

Binaries:
  Node: 20.19.5
  npm: 11.6.4
  Yarn: N/A
  pnpm: 10.2.1
Relevant Packages:
  payload: 3.78.0
  next: 15.5.12
  @payloadcms/db-sqlite: 3.78.0
  @payloadcms/drizzle: 3.78.0
  @payloadcms/graphql: 3.78.0
  @payloadcms/live-preview: 3.78.0
  @payloadcms/live-preview-react: 3.78.0
  @payloadcms/next/utilities: 3.78.0
  @payloadcms/richtext-lexical: 3.78.0
  @payloadcms/translations: 3.78.0
  @payloadcms/ui/shared: 3.78.0
  react: 19.2.4
  react-dom: 19.2.4
Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.3.0: Wed Jan 28 20:53:05 PST 2026; root:xnu-12377.81.4~5/RELEASE_ARM64_T6020
  Available memory (MB): 65536
  Available CPU cores: 12

Start by reproducing the issue in the admin panel using the documented Add Content and Add Below entry points with a blocks field configured with filterOptions. Trace how each action opens the add-blocks modal; done means Add Below shows the same filtered block choices as Add Content, including the default-template RichText-only case.