step 1, 2 and 3 of the implementation plan

app/Models/Session.php

@@ -0,0 +1,84 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+final class Session extends Model
+{
+    protected $table = 'questionnaire_sessions';
+
+    /**
+     * Fillable attributes for mass assignment.
+     */
+    protected $fillable = [
+        'user_id',
+        'category_id',
+        'screening_id',
+        'status',
+        'score',
+        'result',
+        'basic_info',
+        'additional_comments',
+        'completed_at',
+    ];
+
+    /**
+     * Cast attributes to specific types.
+     */
+    protected function casts(): array
+    {
+        return [
+            'user_id' => 'integer',
+            'category_id' => 'integer',
+            'screening_id' => 'integer',
+            'score' => 'integer',
+            'basic_info' => 'array',
+            'completed_at' => 'datetime',
+        ];
+    }
+
+    /**
+     * Get the user that owns this session.
+     */
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    /**
+     * Get the category for this session.
+     */
+    public function category(): BelongsTo
+    {
+        return $this->belongsTo(Category::class);
+    }
+
+    /**
+     * Get the screening that preceded this session.
+     */
+    public function screening(): BelongsTo
+    {
+        return $this->belongsTo(Screening::class);
+    }
+
+    /**
+     * Get all answers for this session.
+     */
+    public function answers(): HasMany
+    {
+        return $this->hasMany(Answer::class);
+    }
+
+    /**
+     * Get all logs for this session.
+     */
+    public function logs(): HasMany
+    {
+        return $this->hasMany(Log::class);
+    }
+}