better-data: Extending the Presenter

For library maintainers adding output transformations to the better-data Presenter — a new fluent builder method (mask, formatPhone, hideIfBlank), a PresentationContext flag (admin vs REST vs export), or a Formatter helper. The Presenter is the read-side projection layer between a DataObject and whatever consumes it (admin UI, REST response, audit log).

Misconception this skill corrects

"The Presenter is readonly like the DataObject — every fluent method must clone and return a new instance."

Wrong. The DataObject is readonly, the Presenter is intentionally a mutable builder. Look at src/Presenter/Presenter.php:65-89 — class Presenter (not final readonly class), with private mutable properties $only, $hidden, $rename, $computed, $presets, $includeSensitive. Each fluent method assigns to $this->... and returns $this. This is deliberate — chained calls share state, repeated calls override, and there's no clone overhead.

What IS immutable: $this->dto is protected readonly DataObject and never gets reassigned. The builder mutates ITS state to control HOW the DTO is rendered; the DTO itself stays untouched.

The "don't mutate permanently" rule from older docs means: don't introduce a method whose effect can't be reset by a subsequent method or context swap. A method that pushes to a private array is fine; a method that writes to a static cache or to the wrapped DTO would be a regression.

Other AI-prone misconceptions:

• "I'll add getSecretRevealed() so consumers don't need ->reveal() boilerplate." Wrong — the explicit $dto->field->reveal() inside a compute() closure IS the security audit point. Adding a bypass method is the same regression as a debug-mode log of secrets.
• "CollectionPresenter is a separate Presenter; I just add the method there too with copy/paste logic." Wrong — CollectionPresenter records each configurer as a closure on $this->configurers (src/Presenter/CollectionPresenter.php:30-44) and replays it on every item via the per-item Presenter. The pattern is $this->configurers[] = static fn (Presenter $p) => $p->yourMethod(...);. No business logic on the collection side.