Control-only inline renderer for ONE entity field — the embeddable primitive under FormBuilder.build_field/3's full form blocks. Hosts that lay records out their own way (compact rows, table cells, chips) render <.field_input> per field and keep full ownership of layout, labels, and persistence, while every field type — including ones added to entities later — renders correctly without host changes.

The save contract

The host wraps its inputs in a <form phx-change="..." phx-submit="..."> it owns (include hidden inputs for row identity — a record uuid — and read _target to know which field changed). phx-submit is load-bearing even when the change event does all the saving: a form with phx-change but no phx-submit is treated as external by LiveView, so Enter in a typed input native-submits and navigates away, killing the socket. Point it anywhere harmless — a clause that no-ops on payloads without _target works.

• Typed inputs (text, textarea, email, url, rich_text, number, date) carry phx-debounce="blur", so the form's change event fires on blur/enter — not per keystroke.
• Discrete inputs (boolean toggle, select, radio, checkbox group) fire immediately. Booleans pair the checkbox with a hidden "false" input and checkbox groups a hidden "", so the change payload always carries the key even when everything is unticked. Checkbox groups submit under name[] (not the bare name), so the host reads a list at that key — cast_field/2 normalizes it, dropping the hidden "" entry.
• Media references (image, video) are not form inputs at all: they render the current file (thumbnail for images) plus Choose/Clear buttons that push the host's on_pick/on_clear events with phx-value-field={field key} and any pick_params. The host opens its media picker (e.g. core's MediaSelectorModal) and writes the chosen storage file uuid through its own save path.

Cast the change payload with PhoenixKitEntities.FormBuilder.cast_field/2 before persisting — it applies the same per-type coercion and validation the full form pipeline uses.

Nested forms are invalid HTML: this component renders bare controls precisely so it can live inside whatever form (or none) the host has; the host is responsible for the form context.

Example

<form
  id={"row-#{value.uuid}"}
  phx-change="extras_changed"
  phx-submit="extras_changed"
>
  <input type="hidden" name="uuid" value={value.uuid} />
  <.field_input
    :for={field <- @entity.fields_definition}
    field={field}
    name={"extras[#{field["key"]}]"}
    value={value.data[field["key"]]}
    size="xs"
    on_pick="pick_extra_media"
    on_clear="clear_extra_media"
    pick_params={%{"uuid" => value.uuid}}
  />
</form>