feat: log status changes to an Application as an Interaction

.ai/decisions.md

@@ -93,3 +93,26 @@ Rejected as more tooling than the actual risk (single author, single
 codebase) justifies right now.
 
 ---
+
+## Status-change observer lives inline on `Application`, not a separate `Observer` class
+_Recorded: 2026-09-03_
+
+Laravel supports both a dedicated `Observer` class (registered via
+`#[ObservedBy]` or in a service provider) and reacting to model events
+directly inside the model's own `boot()`. The spec (`v1.md`) only specifies
+the *effect* ("via an observer on `Application`"), not which of the two.
+
+**Why:** kept inline in `Application::boot()` rather than split into
+`app/Observers/ApplicationObserver.php`. A separate Observer class is easy
+to forget exists — it's registered elsewhere, invisible from the model
+itself, and its file naturally goes unopened while working on the model.
+Inline keeps the status-change side effect visible right next to `status`'s
+own logic (`canTransitionTo()`), at the cost of a slightly larger model
+class.
+
+**Alternative considered:** a dedicated `ApplicationObserver` class,
+Laravel's more common convention for this. Rejected for now on the
+forgettability argument above; revisit if `Application` accumulates enough
+inline event handling to outweigh that.
+
+---

app/Models/Application.php

@@ -5,6 +5,7 @@
 namespace App\Models;
 
 use App\Enums\ApplicationStatus;
+use App\Enums\InteractionType;
 use Carbon\CarbonImmutable;
 use Database\Factories\ApplicationFactory;
 use Illuminate\Database\Eloquent\Collection;
@@ -41,6 +42,29 @@ final class Application extends Model
         'notes',
     ];
 
+    protected static function boot(): void
+    {
+        parent::boot();
+
+        self::updated(function (Application $application) {
+            if (! $application->wasChanged('status')) {
+                return;
+            }
+
+            /** @var array<string, string> $previous */
+            $previous = $application->getPrevious();
+            $application->interactions()->create([
+                'type' => InteractionType::STATUS_CHANGE,
+                'occurred_at' => CarbonImmutable::now(),
+                'body' => sprintf(
+                    'Status changed from %s to %s.',
+                    $previous['status'],
+                    $application->status->value,
+                ),
+            ]);
+        });
+    }
+
     /** @phpstan-return BelongsTo<Company, $this> */
     public function company(): BelongsTo
     {

tests/Feature/ApplicationStatusChangeTest.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\Application;
+use App\Models\Interaction;
+
+test('an interaction is created when the status of an application is updated', function () {
+    $application = Application::factory()
+        ->lead()
+        ->create();
+    $application->update(['status' => 'applied']);
+
+    /** @var Interaction $interaction */
+    $interaction = $application->interactions()->first();
+
+    expect(Interaction::query()->count())
+        ->toBe(1)
+        ->and($interaction->type->value)
+        ->toBe('status_change');
+});