[duncanmcclean]

This pull request fixes an issue where entries whose link fields point at each other (A → B → C → A) would cause infinite recursion when the entry was converted to an array or JSON, eg. via Entry::toArray(), json_encode($entry) or {{ collection:pages as="menu" }}{{ menu | to_json }}.

This was happening because AugmentedCollection::toArray(), when evaluating, eagerly walks whatever ArrayableLink::toArray() returns. That's the full augmented array of the linked entry, which contains its own link field, and so on until the stack overflows. Even without a cycle, this expanded the whole link graph into the array.

This PR fixes it by representing links shallowly in evaluated arrays, matching how they're already represented in JSON since #11375. ArrayableLink gains a toShallowArray() method, which jsonSerialize() now uses too. Deep {{ link:field }} / $link['field'] access in templates is unchanged.

Fixes #9105

[duncanmcclean]

Closing this one. On reflection, it's breaking: for links that don't form a cycle, Entry::toArray(), json_encode($entry) and {{ entries | to_json }} would go from returning the linked entry's full data to only id, title, url, permalink and api_url. Anyone reading a custom field out of that JSON would lose it in a minor release.

A different approach is needed. The nested evaluation happens inside the AugmentedCollection::toArray() closure, so a cycle guard can live there: track the link targets being expanded and only fall back to the shallow array when a target repeats. That keeps today's output for everyone without cycles and fixes #9105 for those with them.