fix: do not set plan_id on checkout creation; drop redundant guards

Two issues from review:

1. BillingController::checkout was setting plan_id immediately after
   creating the Stripe Checkout session, before the user actually paid.
   If the user abandoned checkout, the account ended up with a plan it
   never paid for. Plan activation is now driven exclusively by the
   customer.subscription.created webhook, which fires only after a
   successful payment.

2. The 'if (\$account->wasChanged('plan_id')) { ... }' guards around
   forgetPlanFeatureCache() were tautological — Eloquent's update()
   already short-circuits when nothing changed, and Pennant forget()
   is idempotent, so an extra cache clear when the plan didn't move
   is harmless. Removing the guards keeps the listener and swap path
   readable.

app/Http/Controllers/App/BillingController.php

@@ -70,12 +70,6 @@ public function checkout(Request $request, Plan $plan): SymfonyResponse|Redirect
             'cancel_url' => route('app.subscribe'),
         ]);
 
-        $account->update(['plan_id' => $plan->id]);
-
-        if ($account->wasChanged('plan_id')) {
-            $account->forgetPlanFeatureCache();
-        }
-
         return Inertia::location($checkoutSession->url);
     }
 
@@ -167,10 +161,7 @@ public function swap(Request $request, Plan $plan): RedirectResponse
 
         $subscription->swap($priceId);
         $account->update(['plan_id' => $plan->id]);
-
-        if ($account->wasChanged('plan_id')) {
-            $account->forgetPlanFeatureCache();
-        }
+        $account->forgetPlanFeatureCache();
 
         return redirect()->route('app.billing.index')
             ->with('flash.success', __('billing.flash.plan_changed', ['plan' => $plan->name]));

app/Listeners/StripeEventListener.php

@@ -53,10 +53,7 @@ protected function handleSubscriptionCreated(Account $account, array $payload):
 
         if ($plan = $this->resolvePlanFromSubscriptionItems($payload, $account)) {
             $account->update(['plan_id' => $plan->id]);
-
-            if ($account->wasChanged('plan_id')) {
-                $account->forgetPlanFeatureCache();
-            }
+            $account->forgetPlanFeatureCache();
         }
 
         SubscriptionCreated::dispatch($account);
@@ -78,10 +75,7 @@ protected function handleSubscriptionUpdated(Account $account, array $payload):
 
         if ($plan = $this->resolvePlanFromSubscriptionItems($payload, $account)) {
             $account->update(['plan_id' => $plan->id]);
-
-            if ($account->wasChanged('plan_id')) {
-                $account->forgetPlanFeatureCache();
-            }
+            $account->forgetPlanFeatureCache();
         }
 
         $this->trackPlanChange($account, BillingEvent::Updated, $previousPlan, $payload);
@@ -100,10 +94,7 @@ protected function handleSubscriptionDeleted(Account $account, array $payload):
         $previousPlan = $account->plan?->name;
 
         $account->update(['plan_id' => null]);
-
-        if ($account->wasChanged('plan_id')) {
-            $account->forgetPlanFeatureCache();
-        }
+        $account->forgetPlanFeatureCache();
 
         $this->trackPlanChange($account, BillingEvent::Cancelled, $previousPlan, $payload);
     }

tests/Feature/Listeners/StripeEventListenerTest.php

@@ -447,30 +447,3 @@
     expect(DB::table('features')->where('scope', 'account|'.$this->account->id)->count())
         ->toBe(0);
 });
-
-test('subscription updated with same plan does not flush the pennant cache', function () {
-    $starter = Plan::query()->where('slug', 'starter')->firstOrFail();
-    $this->account->update(['plan_id' => $starter->id]);
-
-    Feature::for($this->account)->value(WorkspaceLimit::class);
-
-    $cachedRow = DB::table('features')
-        ->where('scope', 'account|'.$this->account->id)
-        ->first();
-
-    expect($cachedRow)->not->toBeNull();
-
-    $this->listener->handle(new WebhookReceived([
-        'type' => 'customer.subscription.updated',
-        'data' => ['object' => [
-            'customer' => 'cus_test123',
-            'items' => ['data' => [['price' => ['id' => 'price_starter_monthly']]]],
-        ]],
-    ]));
-
-    $stillCachedRow = DB::table('features')
-        ->where('scope', 'account|'.$this->account->id)
-        ->first();
-
-    expect($stillCachedRow->id)->toBe($cachedRow->id);
-});