step 1, 2 and 3 of the implementation plan

app/Models/Log.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+final class Log extends Model
+{
+    /**
+     * Disable the updated_at timestamp for append-only logs.
+     */
+    public const UPDATED_AT = null;
+
+    /**
+     * Fillable attributes for mass assignment.
+     */
+    protected $fillable = [
+        'user_id',
+        'session_id',
+        'category_id',
+        'action',
+        'metadata',
+    ];
+
+    /**
+     * Cast attributes to specific types.
+     */
+    protected function casts(): array
+    {
+        return [
+            'user_id' => 'integer',
+            'session_id' => 'integer',
+            'category_id' => 'integer',
+            'metadata' => 'array',
+        ];
+    }
+
+    /**
+     * Boot the model and prevent updates and deletes.
+     */
+    protected static function booted(): void
+    {
+        self::updating(function (): bool {
+            return false;
+        });
+
+        self::deleting(function (): bool {
+            return false;
+        });
+    }
+
+    /**
+     * Get the user that performed the logged action.
+     */
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    /**
+     * Get the session associated with this log entry.
+     */
+    public function session(): BelongsTo
+    {
+        return $this->belongsTo(Session::class);
+    }
+
+    /**
+     * Get the category associated with this log entry.
+     */
+    public function category(): BelongsTo
+    {
+        return $this->belongsTo(Category::class);
+    }
+}