fix: key Tia worker partials per process to survive batch recycling (#1782)

* fix: key Tia worker partials per process to survive batch recycling

* test(tia): refresh visual snapshots for the worker token test

---------

Co-authored-by: Punyapal Shah <53343069+MrPunyapal@users.noreply.github.com>

tests/Unit/Plugins/Tia/WorkerToken.php

@@ -0,0 +1,39 @@
+<?php
+
+use Pest\Plugins\Tia;
+
+function tiaWorkerToken(): string
+{
+    $tia = new ReflectionClass(Tia::class)->newInstanceWithoutConstructor();
+
+    return new ReflectionMethod($tia, 'workerToken')->invoke($tia);
+}
+
+beforeEach(function (): void {
+    unset(
+        $_SERVER['TEST_TOKEN'],
+        $_ENV['TEST_TOKEN'],
+        $_SERVER['UNIQUE_TEST_TOKEN'],
+        $_ENV['UNIQUE_TEST_TOKEN'],
+    );
+});
+
+test('prefers the per-process UNIQUE_TEST_TOKEN over the per-slot TEST_TOKEN, so two workers recycled into the same slot get different tokens', function (): void {
+    $_SERVER['TEST_TOKEN'] = '2';
+
+    $_SERVER['UNIQUE_TEST_TOKEN'] = '2_6a690d236824c';
+    $processA = tiaWorkerToken();
+
+    $_SERVER['UNIQUE_TEST_TOKEN'] = '2_9f31be04117a';
+    $processB = tiaWorkerToken();
+
+    expect($processA)->toBe('2_6a690d236824c')
+        ->and($processB)->toBe('2_9f31be04117a')
+        ->and($processA)->not->toBe($processB);
+});
+
+test('falls back to TEST_TOKEN when UNIQUE_TEST_TOKEN is absent', function (): void {
+    $_SERVER['TEST_TOKEN'] = '3';
+
+    expect(tiaWorkerToken())->toBe('3');
+});