Add integration test for .ini file extension loading

Add test case that verifies PHP extensions specified in
.bp-config/php/php.ini.d/*.ini files are loaded during both composer
install (build-time) and application runtime.

Test fixture includes:
- .bp-config/php/php.ini.d/custom.ini with extension=apcu.so
- composer.json requiring ext-apcu with verification scripts
- index.php displaying loaded extensions at runtime

The test validates that:
- APCu extension loads during composer install
- Extension is available at application runtime
- Build logs show successful extension configuration

Author: ramonskie

fixtures/composer_with_extensions/.bp-config/php/php.ini.d/custom.ini

@@ -0,0 +1,2 @@
+[PHP]
+extension=apcu.so

fixtures/composer_with_extensions/composer.json

@@ -0,0 +1,14 @@
+{
+    "name": "cloudfoundry/composer_with_extensions",
+    "description": "Test app requiring PHP extensions during composer install",
+    "require": {
+        "php": ">=8.1",
+        "ext-apcu": "*"
+    },
+    "scripts": {
+        "post-install-cmd": [
+            "php -r \"if (!extension_loaded('apcu')) { echo 'FATAL: apcu extension not loaded during composer!'; exit(1); }\"",
+            "php -r \"echo 'SUCCESS: All required extensions are loaded during composer install\\n';\""
+        ]
+    }
+}

fixtures/composer_with_extensions/composer.lock

@@ -0,0 +1,22 @@
+<?php
+echo "<h1>PHP Extensions Test</h1>";
+echo "<h2>PHP Version: " . phpversion() . "</h2>";
+
+$required_extensions = ['apcu'];
+
+echo "<h3>Required Extensions Status:</h3>";
+echo "<ul>";
+foreach ($required_extensions as $ext) {
+    $loaded = extension_loaded($ext);
+    $status = $loaded ? '✓ LOADED' : '✗ NOT LOADED';
+    echo "<li><strong>$ext:</strong> $status</li>";
+}
+echo "</ul>";
+
+echo "<h3>All Loaded Extensions:</h3>";
+echo "<ul>";
+foreach (get_loaded_extensions() as $ext) {
+    echo "<li>$ext</li>";
+}
+echo "</ul>";
+?>

fixtures/composer_with_extensions/htdocs/index.php

@@ -110,5 +110,29 @@ func testComposer(platform switchblade.Platform, fixtures string) func(*testing.
 				})
 			})
 		}
+
+		context("composer app with extensions in .bp-config/php/php.ini.d", func() {
+			it("loads extensions during composer install and at runtime", func() {
+				deployment, logs, err := platform.Deploy.
+					WithEnv(map[string]string{
+						"COMPOSER_GITHUB_OAUTH_TOKEN": os.Getenv("COMPOSER_GITHUB_OAUTH_TOKEN"),
+					}).
+					Execute(name, filepath.Join(fixtures, "composer_with_extensions"))
+				Expect(err).NotTo(HaveOccurred())
+
+				// Check build logs first (composer phase)
+				Expect(logs.String()).To(SatisfyAll(
+					ContainSubstring("Loading user-requested extensions from .bp-config/php/php.ini.d"),
+					ContainSubstring("Found 1 extension(s)"),
+					ContainSubstring("Installing Composer dependencies"),
+					ContainSubstring("SUCCESS: All required extensions are loaded during composer install"),
+					Not(ContainSubstring("composer install failed")),
+					Not(ContainSubstring("ERROR")),
+				))
+
+				// Then wait for deployment and check runtime
+				Eventually(deployment).Should(Serve(ContainSubstring("apcu:</strong> ✓ LOADED")))
+			})
+		})
 	}
 }