Model::replicate() should clear the replicate's "-to-Many" dynamic properties

[le-yak]

Assume the most usual One-to-Many relationship (boilerplate code in the collapsible section at the bottom):

Author ◆— Post

When replicating an entity at the "HasMany" side of a relationship (e.g. Author) with Model::replicate(), the resulting entity's dynamic properties may still mistakenly refer to the original entity's relations.

The problem appears if the original entity's relations were loaded before replication.

        $author = new \App\Models\Author();
        $author->save();

        $post = new \App\Models\Post();
        $post->author()->associate($author);
        $post->save();

        // $author has one Post

        /**
         * NOT loading the relationship before replication
        */
        dump('NOT loading the relationship before replication');
        $author1 = $author->replicate();
        dump($author1->posts->count());             // 0 (ok)
        $author1->save();
        dump($author1->posts->count());             // 0 (ok)
        dump($author1->posts()->get()->count());    // 0 (ok)

        /**
         * Loading relationship
        */
        dump('Loading relationship');
        dump($author->posts->count());              // 1 (ok)

        $author2 = $author->replicate();
        dump($author2->posts->count());             // 1 (expected: 0)
        dump($author2->posts()->get()->count());    // 0
        $author2->save();
        dump($author2->posts->count());             // 1 (expected: 0)
        dump($author2->posts()->get()->count());    // 0 (ok)
        $author2->refresh();
        dump($author2->posts->count());             // 0 (ok)

        /**
         * Replicating the One-to- side of the relationship
        */
        dump('Replicating the One-to- side of the relationship');
        dump($post->author !== null);               // true (ok)
        $post2 = $post->replicate();
        $post2->save();
        $post2->refresh();
        dump($post2->author !== null);              // true (ok)

The same behviour is visible when replicating either side of a Many-to-Many relationship.

Expected result:

• the replicated entity's dynamic properties which represent a to-Many relationship are reset
• the documentation should make it clear that only -to-One relations are replicated; in particular, Many-to-Many relationships are NOT replicated (where replicating relations could make sense)

System informations:
Laravel: 8.61.0
PHP: v8.0.10

Models and Migrations

// 0000_00_00_000000_create_one_to_many.php
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateOneToMany extends Migration
{
Schema::create('authors' , function (Blueprint $table) {
    $table->id();
});
Schema::create('posts' , function (Blueprint $table) {
    $table->id();
    $table->foreignId('author_id')->constrained('authors');
});

// Author.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;

class Author extends Model
{
    public $timestamps = false;
    public function posts(): HasMany
    {
        return $this->hasMany(Post::class);
    }
}

// Post.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class Post extends Model
{
    public $timestamps = false;
    
    public function author(): BelongsTo
    {
        return $this->belongsTo(Author::class);
    }
}