Update relationship_not_setup wording to clarify it may also result from missing permissions

[Ikromjon1998]

Summary

When a user lacks read permission on a related collection, the relational interfaces (M2O, O2M, M2M, M2A, Files) showed "The relationship hasn't been configured correctly" — which is misleading since the relationship is correctly configured, the user simply doesn't have access.

This is a follow-up to #26837 with the backend fix requested by reviewers.

What changed

Backend (api/src/services/relations.ts):

• Modified filterForbidden() to differentiate between two cases:
  1. User can't read the many-side (collection/field owning the relation) → relation is still filtered out completely
  2. User can read the many-side but can't read the related collection → relation is kept but marked with related_collection_readable: false

Types (packages/types/src/relations.ts):

• Added optional related_collection_readable?: boolean field to the Relation type

Frontend composables:

• Added relationMissingPermissions computed property to use-relation-m2o.ts, use-relation-o2m.ts, use-relation-m2m.ts, and use-relation-m2a.ts that checks the explicit backend flag
• relationInfo returns undefined when related_collection_readable === false to prevent downstream errors

Frontend interfaces:

• Updated 5 relational interface components to show a permission-specific warning when relationMissingPermissions is true

Translation:

• Added relationship_missing_permissions key to en-US.yaml

Closes #21337

Key design decisions

• The fix is in filterForbidden() on the backend — the root cause — rather than inferring permission issues from meta.special on the frontend
• The related_collection_readable field is optional and backwards compatible — existing consumers that don't know about it will just ignore it
• When undefined, the relation is fully accessible (same behavior as before)

Test plan

• Unit tests for all 4 relation composables (M2O, O2M, M2M, M2A)
• User with read permission on main collection but no read permission on related collection sees "You don't have permission to view the related collection"
• User with a genuinely misconfigured relationship still sees "The relationship hasn't been configured correctly"
• Admin users are unaffected (full access to all relations)

[ComfortablyCoding]

I understand @robluton stated this should be a backend fix but I believe this will potentially expose information about relationships. I wonder if we can simply fix this by updating the relationship_not_setup translation key to be "The relationship is not configured properly or you don’t have permission to access it.". Thoughts?

[robluton]

@ComfortablyCoding I like your thinking here. Nice and simple.

[ComfortablyCoding]

See above comments.

Addressed

[ComfortablyCoding]

Thanks LGTM 🚀 and congratulations on your first contribution to directus! 🥳

[AlexGaillard]

🆒🫘