fix(tests): avoid global env pollution from putenv in SidecarThreadModeRootTest

Replace putenv('DD_TRACE_TEST_SAPI=fpm-fcgi') with a new WebServer::setForceSapi()
method that overrides the SAPI for a single WebServer instance only, without
affecting the global process environment used by all subsequent test classes.

Author: Leiyks

tests/Integrations/Custom/Autoloaded/SidecarThreadModeRootTest.php

@@ -47,15 +47,14 @@ public static function ddSetUpBeforeClass()
             self::markTestSkipped('No unprivileged user found on this system (tried www-data, daemon, nobody)');
         }
 
-        // Force FPM mode regardless of the CI job's DD_TRACE_TEST_SAPI so this
-        // test runs in every test_web_custom matrix entry, not just fpm-fcgi.
-        putenv('DD_TRACE_TEST_SAPI=fpm-fcgi');
-
         parent::ddSetUpBeforeClass();
     }
 
     protected static function configureWebServer(WebServer $server)
     {
+        // Force FPM mode for this test regardless of the CI job's DD_TRACE_TEST_SAPI,
+        // without polluting the global env for other test classes.
+        $server->setForceSapi('fpm-fcgi');
         // Tell FPM to switch worker processes to the unprivileged user after forking.
         $server->setPhpFpmUser(self::$workerUser);
         if (self::$useSudo) {

tests/WebServer.php

@@ -84,6 +84,7 @@ final class WebServer
     private $phpFpmUser = null;
     private $phpFpmGroup = null;
     private $phpFpmSudo = false;
+    private $forceSapi = null;
 
     private $defaultInis = [
         'log_errors' => 'on',
@@ -152,6 +153,11 @@ public function setPhpFpmSudo($sudo = true)
         $this->phpFpmSudo = $sudo;
     }
 
+    public function setForceSapi($sapi)
+    {
+        $this->forceSapi = $sapi;
+    }
+
     public function start()
     {
         if (!isset($this->envs['DD_TRACE_DEBUG'])) {
@@ -196,7 +202,7 @@ public function start()
                 $this->inis
             );
         } else {
-            switch (\getenv('DD_TRACE_TEST_SAPI')) {
+            switch ($this->forceSapi ?? \getenv('DD_TRACE_TEST_SAPI')) {
                 case 'cgi-fcgi':
                     $this->sapi = new PhpCgi(
                         self::FCGI_HOST,