Fix agentic chat toggle being hidden when any self-hosted model exists

Problem: Currently, if any self-hosted model is present in the database, the agentic chat toggle is hidden, and the access check fails due to prevention rules in GlobalPolicy:

Ability.allowed?(root, :access_duo_agentic_chat, project) # => false

This can lead to unintended behavior in hybrid setups. For example, a user may use a self-hosted model (such as Codestral) for code completion but still want to run agent-based chat on GitLab-hosted models. In this case, the agentic chat feature is incorrectly disabled with no UI indication, making it hard to debug.

Update

Fix: Remove the prevention rules in ee/app/policies/ee/global_policy.rb that were blocking agentic chat access when self-hosted models exist. With hybrid mode now GA, these blanket restrictions are no longer needed.

Action Items:

• Remove prevention rules in GlobalPolicy
• Update test expectations to match new behavior
• Enable agentic chat toggle visibility in hybrid setups

Related discussion: Slack thread

To be implemented by: @mhamda (or whoever takes it on from groupcustom models)

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