diff --git a/.ddev/config.yaml b/.ddev/config.yaml
new file mode 100644
index 0000000000..8ccd9b9c76
--- /dev/null
+++ b/.ddev/config.yaml
@@ -0,0 +1,20 @@
+name: wordcamp
+type: php
+docroot: public_html/mu
+php_version: "8.5"
+webserver_type: nginx-fpm
+database:
+  type: mariadb
+  version: "10.11"
+disable_settings_management: true
+additional_fqdns:
+  - wordcamp.test
+  - central.wordcamp.test
+  - seattle.wordcamp.test
+  - shinynew.wordcamp.test
+  - narnia.wordcamp.test
+  - events.wordpress.test
+  - campus.wordpress.test
+hooks:
+  post-start:
+    - exec: bash /var/www/html/.ddev/setup.sh
diff --git a/.ddev/nginx/multisite.conf b/.ddev/nginx/multisite.conf
new file mode 100644
index 0000000000..1794c15846
--- /dev/null
+++ b/.ddev/nginx/multisite.conf
@@ -0,0 +1,28 @@
+# Multisite rewrite rules for WordCamp.org
+# Adapted from .docker/config/nginx.conf
+
+# Rewrite ms-files for uploaded media.
+rewrite ^/files/(.*)$ /wp-includes/ms-files.php?file=$1;
+
+# Rewrite multisite subdirectory paths (e.g., /2023/wp-admin/).
+if (!-e $request_filename) {
+    rewrite ^/[_0-9a-zA-Z-]+(/wp-.*) $1 last;
+    rewrite ^/[_0-9a-zA-Z-]+.*(/wp-admin/.*\.php)$ $1 last;
+    rewrite ^/[_0-9a-zA-Z-]+(/.*\.php)$ $1 last;
+    rewrite "/\d{4}/files/(.+)$" /wp-includes/ms-files.php?file=$1 last;
+}
+
+# Events network 3-level path rewrites (e.g., /rome/2024/training/wp-admin/).
+if ( $host = "events.wordpress.test" ) {
+    rewrite "/[\w-]+/\d{4}/[\w-]+/wp-(admin|content|includes)(.*)" /wp-$1$2 last;
+    rewrite "/[\w-]+/\d{4}/[\w-]+/wp-(.*).php(.*)" /wp-$1.php$2 last;
+    rewrite "/[\w-]+/\d{4}/[\w-]+/xmlrpc\.php" /xmlrpc.php last;
+    rewrite "/[\w-]+/\d{4}/[\w-]+/files/(.+)$" /wp-includes/ms-files.php?file=$1 last;
+}
+
+# Serve wp-content from the parent directory (public_html/, not public_html/mu/).
+location ~* /wp-content/.*\.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf)$ {
+    root /var/www/html/public_html;
+    expires max;
+    log_not_found off;
+}
diff --git a/.ddev/setup.sh b/.ddev/setup.sh
new file mode 100755
index 0000000000..903a1212e2
--- /dev/null
+++ b/.ddev/setup.sh
@@ -0,0 +1,58 @@
+#!/bin/bash
+#
+# Idempotent DDEV post-start setup script for WordCamp.org.
+# Runs inside the web container after `ddev start`.
+#
+
+set -e
+
+PROJECT_ROOT="/var/www/html"
+WP_DIR="$PROJECT_ROOT/public_html/mu"
+WP_CONFIG="$PROJECT_ROOT/public_html/wp-config.php"
+SEED_SQL="$PROJECT_ROOT/.docker/data/wordcamp_dev.sql"
+
+# 1. Download WordPress core if not present.
+if [ ! -f "$WP_DIR/wp-includes/version.php" ]; then
+    echo "Downloading WordPress core..."
+    mkdir -p "$WP_DIR"
+    wp core download --path="$WP_DIR" --skip-content
+fi
+
+# 2. Copy wp-config.php if not present.
+if [ ! -f "$WP_CONFIG" ]; then
+    echo "Copying wp-config.php..."
+    cp "$PROJECT_ROOT/.ddev/wp-config-ddev.php" "$WP_CONFIG"
+fi
+
+# 3. Import seed database if tables don't exist.
+if ! wp db check --path="$WP_DIR" 2>/dev/null | grep -q "wc_options"; then
+    if [ -f "$SEED_SQL" ]; then
+        echo "Importing seed database..."
+        wp db import "$SEED_SQL" --path="$WP_DIR"
+    else
+        echo "Warning: Seed database not found at $SEED_SQL"
+    fi
+fi
+
+# 4. Create placeholder build files for mu-plugins/blocks.
+BLOCKS_DIR="$PROJECT_ROOT/public_html/wp-content/mu-plugins/blocks/source"
+if [ -d "$BLOCKS_DIR" ]; then
+    for dir in "$BLOCKS_DIR"/*/; do
+        block_name=$(basename "$dir")
+        build_dir="$PROJECT_ROOT/public_html/wp-content/mu-plugins/blocks/build/$block_name"
+        if [ ! -d "$build_dir" ]; then
+            mkdir -p "$build_dir"
+            echo '(()=>{"use strict";})();' > "$build_dir/index.js"
+            echo '{"apiVersion":2}' > "$build_dir/block.json"
+        fi
+    done
+fi
+
+# 5. Install WP test suite for PHPUnit.
+WP_TESTS_DIR="/tmp/wp/wordpress-tests-lib"
+if [ ! -d "$WP_TESTS_DIR/includes" ]; then
+    echo "Installing WordPress test suite..."
+    bash "$PROJECT_ROOT/.docker/bin/install-wp-tests.sh" wcorg_test db db db latest
+fi
+
+echo "DDEV setup complete!"
diff --git a/.ddev/web-build/Dockerfile b/.ddev/web-build/Dockerfile
new file mode 100644
index 0000000000..208e9503a7
--- /dev/null
+++ b/.ddev/web-build/Dockerfile
@@ -0,0 +1 @@
+RUN apt-get update && apt-get install -y subversion && rm -rf /var/lib/apt/lists/*
diff --git a/.ddev/wp-config-ddev.php b/.ddev/wp-config-ddev.php
new file mode 100644
index 0000000000..881262c910
--- /dev/null
+++ b/.ddev/wp-config-ddev.php
@@ -0,0 +1,227 @@
+<?php
+/**
+ * WordCamp.org configuration file for DDEV.
+ *
+ * This is copied to public_html/wp-config.php by the setup script.
+ * Adapted from .docker/wp-config.php with DDEV-specific database credentials.
+ */
+
+define( 'IS_WORDCAMP_NETWORK', true );
+
+/**
+ * The environment in which the WordCamp codebase is currently running.
+ *
+ * There are a few different values that this might contain that have implications in the code:
+ *
+ * - `production`:  Used on the production server. Should not be used anywhere else.
+ * - `development`: The catchall value for non-production environments. Currently used on wporg sandboxes.
+ * - `local`:       The value used for local development environments, where the domain is wordcamp.test and some
+ *                  functionality that relies on remote connections may not be available.
+ */
+define( 'WORDCAMP_ENVIRONMENT', 'local' );
+define( 'WP_ENVIRONMENT_TYPE', 'local' );
+
+/*
+ * Database
+ */
+define( 'DB_NAME',     'db' );
+define( 'DB_USER',     'db' );
+define( 'DB_PASSWORD', 'db' );
+define( 'DB_HOST',     'db' );
+
+// Force utf8mb4.
+define( 'DB_CHARSET', 'utf8mb4' );
+define( 'DB_COLLATE', 'utf8mb4_general_ci' );
+
+define( 'CUSTOM_USER_TABLE',      'wc_users'    );
+define( 'CUSTOM_USER_META_TABLE', 'wc_usermeta' );
+
+$table_prefix = 'wc_'; // phpcs:ignore WordPress.WP.GlobalVariablesOverride
+
+/*
+ * Multisite
+ */
+const WORDCAMP_NETWORK_ID   = 1;
+const WORDCAMP_ROOT_BLOG_ID = 5;
+const EVENTS_NETWORK_ID     = 2;
+const EVENTS_ROOT_BLOG_ID   = 47;
+const CAMPUS_NETWORK_ID     = 3;
+const CAMPUS_ROOT_BLOG_ID   = 47;
+
+switch ( strtolower( $_SERVER['HTTP_HOST'] ) ) {
+	case 'campus.wordpress.test':
+		define( 'SITE_ID_CURRENT_SITE',  CAMPUS_NETWORK_ID );
+		define( 'BLOG_ID_CURRENT_SITE',  EVENTS_ROOT_BLOG_ID );
+		define( 'DOMAIN_CURRENT_SITE',   'campus.wordpress.test' );
+		define( 'SUBDOMAIN_INSTALL',     false );
+		define( 'NOBLOGREDIRECT',        'https://events.wordpress.test/campusconnect/' );
+		define( 'CLI_HOSTNAME_OVERRIDE', 'campus.wordpress.test' );
+		break;
+
+	case 'events.wordpress.test':
+		define( 'SITE_ID_CURRENT_SITE',  EVENTS_NETWORK_ID );
+		define( 'BLOG_ID_CURRENT_SITE',  EVENTS_ROOT_BLOG_ID );
+		define( 'DOMAIN_CURRENT_SITE',   'events.wordpress.test' );
+		define( 'SUBDOMAIN_INSTALL',     false );
+		// NOBLOGREDIRECT is intentionally omitted so that the 404 template works.
+		define( 'CLI_HOSTNAME_OVERRIDE', 'events.wordpress.test' );
+		break;
+
+	case 'wordcamp.test':
+	case 'buddycamp.test':
+	default:
+		define( 'SITE_ID_CURRENT_SITE',  WORDCAMP_NETWORK_ID );
+		define( 'BLOG_ID_CURRENT_SITE',  WORDCAMP_ROOT_BLOG_ID );
+		define( 'DOMAIN_CURRENT_SITE',   'buddycamp.test' === $_SERVER['HTTP_HOST'] ? 'buddycamp.test' : 'wordcamp.test' );
+		define( 'SUBDOMAIN_INSTALL',     true );
+		define( 'NOBLOGREDIRECT',        'https://central.wordcamp.test' );
+		define( 'CLI_HOSTNAME_OVERRIDE', 'wordcamp.test' );
+		break;
+}
+
+define( 'MULTISITE',         true );
+define( 'SUNRISE',           true );
+define( 'PATH_CURRENT_SITE', '/' );
+
+
+/*
+ * Logging/Debugging
+ */
+define( 'WP_DEBUG',         true );
+define( 'WP_DEBUG_LOG',     true );
+define( 'WP_DEBUG_DISPLAY', true );
+define( 'SAVEQUERIES',      true );
+define( 'DIEONDBERROR',     false );
+define( 'SCRIPT_DEBUG',     false );
+define( 'JETPACK_DEV_DEBUG', true );
+
+
+/*
+ * Salts
+ *
+ * It doesn't matter for local environments, but use `wp config shuffle-salts` to change this in production
+ * environments, because generating the keys locally is safer than using the API (and exposing the keys to
+ * your OS/browser if you copy/paste, etc).
+ */
+define( 'AUTH_KEY',                          'put your unique phrase here' );
+define( 'SECURE_AUTH_KEY',                   'put your unique phrase here' );
+define( 'LOGGED_IN_KEY',                     'put your unique phrase here' );
+define( 'NONCE_KEY',                         'put your unique phrase here' );
+define( 'AUTH_SALT',                         'put your unique phrase here' );
+define( 'SECURE_AUTH_SALT',                  'put your unique phrase here' );
+define( 'LOGGED_IN_SALT',                    'put your unique phrase here' );
+define( 'NONCE_SALT',                        'put your unique phrase here' );
+define( 'ORGANIZER_SURVEY_ACCESS_TOKEN_KEY', 'put your unique phrase here' );
+
+
+/*
+ * Misc
+ */
+define( 'WPLANG',          '' );
+define( 'WP_CONTENT_DIR', __DIR__ . '/wp-content' );
+define( 'WP_CONTENT_URL', 'https://' . preg_replace( '/[^-_.0-9a-z:]/i', '', $_SERVER['HTTP_HOST'] ) . '/wp-content' );
+define( 'WP_TEMP_DIR',    '/tmp' );
+
+define( 'FORCE_SSL_ADMIN',          true );
+define( 'DISALLOW_UNFILTERED_HTML', true );
+
+define( 'WORDCAMP_SCRIPT_DIR',     __DIR__ . '/bin' );
+define( 'WP_CLI_SCRIPT_DIR',       WORDCAMP_SCRIPT_DIR . '/wp-cli/' );
+define( 'SCRIPT_BACKUP_DIRECTORY', WP_TEMP_DIR );
+define( 'WORDCAMP_UTILITIES_DIR',  WP_CONTENT_DIR . '/mu-plugins/utilities' );
+
+define( 'EMAIL_DEVELOPER_NOTIFICATIONS', 'developers@example.test' );
+define( 'EMAIL_CENTRAL_SUPPORT',         'support@wordcamp.test' );
+
+$trusted_deputies = array(
+	6, // contributorrole.
+);
+
+$wcorg_subroles = array(
+	// contributorrole.
+	6 => array(
+		'wordcamp_wrangler',
+		'meetup_wrangler',
+		'mentor_manager',
+		'report_viewer',
+	),
+);
+
+/*
+ * Third party services
+ */
+define( 'SLACK_ERROR_REPORT_URL',      '(Optional) you can configure slack and add your webhook url. Errors will be posted to this slack url' );
+define( 'WORDCAMP_LOGS_SLACK_CHANNEL', '(Optional) @your_slack_username' );
+define( 'WORDCAMP_LOGS_JETPACK_SLACK_CHANNEL',   '(Optional) @your_slack_username' );
+define( 'WORDCAMP_LOGS_GUTENBERG_SLACK_CHANNEL', '(Optional) @your_slack_username' );
+
+define( 'TWITTER_CONSUMER_KEY_WORDCAMP_CENTRAL',    '' );
+define( 'TWITTER_CONSUMER_SECRET_WORDCAMP_CENTRAL', '' );
+define( 'TWITTER_BEARER_TOKEN_WORDCAMP_CENTRAL',    '' );
+
+define( 'WORDCAMP_QBO_HMAC_KEY',        'localhmac' );
+
+define( 'WORDCAMP_SANDBOX_QBO_CLIENT_ID',        "(Optional) your app's development client ID key goes here" );
+define( 'WORDCAMP_SANDBOX_QBO_CLIENT_SECRET',    "(Optional) your app's development client secret key goes here" );
+define( 'WORDCAMP_PRODUCTION_QBO_CLIENT_ID',     '' );
+define( 'WORDCAMP_PRODUCTION_QBO_CLIENT_SECRET', '' );
+
+define( 'REMOTE_CSS_GITHUB_ID',         '' );
+define( 'REMOTE_CSS_GITHUB_SECRET',     '' );
+
+define( 'WORDCAMP_LE_HELPER_API_KEY', '' );
+define( 'GENDERIZE_IO_API_KEY',       '' );
+
+define( 'WC_SANDBOX_PAYPAL_NVP_USERNAME',  '' );
+define( 'WC_SANDBOX_PAYPAL_NVP_PASSWORD',  '' );
+define( 'WC_SANDBOX_PAYPAL_NVP_SIGNATURE', '' );
+define( 'WPCS_PAYPAL_NVP_USERNAME',        '' );
+define( 'WPCS_PAYPAL_NVP_PASSWORD',        '' );
+define( 'WPCS_PAYPAL_NVP_SIGNATURE',       '' );
+
+define( 'WORDCAMP_CAMPTIX_STRIPE_TEST_PUBLIC', '' );
+define( 'WORDCAMP_CAMPTIX_STRIPE_TEST_SECRET', '' );
+define( 'WORDCAMP_CAMPTIX_STRIPE_LIVE_PUBLIC', '' );
+define( 'WORDCAMP_CAMPTIX_STRIPE_LIVE_SECRET', '' );
+
+define( 'WORDCAMP_PAYMENTS_ENCRYPTION_KEY',         '' );
+define( 'WORDCAMP_PAYMENTS_HMAC_KEY',               '' );
+define( 'WORDCAMP_PAYMENT_STRIPE_HMAC',             '' );
+define( 'WORDCAMP_PAYMENT_STRIPE_PUBLISHABLE',      '' );
+define( 'WORDCAMP_PAYMENT_STRIPE_SECRET',           '' );
+define( 'WORDCAMP_PAYMENT_STRIPE_PUBLISHABLE_LIVE', '' );
+define( 'WORDCAMP_PAYMENT_STRIPE_SECRET_LIVE',      '' );
+
+define( 'WORDCAMP_PROD_GOOGLE_MAPS_API_KEY', '' );
+define( 'WORDCAMP_DEV_GOOGLE_MAPS_API_KEY', '' );
+
+define( 'MEETUP_API_BASE_URL', 'https://api.meetup.com/' );
+define( 'MEETUP_MEMBER_ID',     72560962                 );
+define( 'MEETUP_OAUTH_CONSUMER_KEY', '' );
+define( 'MEETUP_OAUTH_CONSUMER_SECRET', '' );
+define( 'MEETUP_OAUTH_CONSUMER_REDIRECT_URI', '' );
+define( 'MEETUP_USER_EMAIL', '' );
+define( 'MEETUP_USER_PASSWORD', '' );
+
+define( 'WORDCAMP_FIXER_API_KEY', '' );
+define( 'WORDCAMP_OXR_API_KEY',   '' );
+
+
+/*
+ * WP Super Cache
+ */
+define( 'WP_CACHE',       true );
+define( 'WPCACHEHOME',    WP_CONTENT_DIR . '/plugins/wp-super-cache/' );
+define( 'SUBMITDISABLED', false ); // Work around https://github.com/Automattic/wp-super-cache/issues/213.
+define( 'WP_CACHE_PAGE_SECRET',    '' );
+define( 'WP_CACHE_DEBUG_USERNAME', '' );
+
+
+/*
+ * Bootstrap WordPress
+ */
+if ( ! defined('ABSPATH') ) {
+	define( 'ABSPATH', __DIR__ . '/mu/' );
+}
+
+require_once ABSPATH . 'wp-settings.php';
diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index dbec3deb39..d71cce7e5c 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -55,17 +55,6 @@ jobs:
       matrix:
         php-version: ['8.1', '8.4', '8.5']
 
-    services:
-      mysql:
-        image: mysql:5.7
-        env:
-          MYSQL_ALLOW_EMPTY_PASSWORD: false
-          MYSQL_ROOT_PASSWORD: root
-          MYSQL_DATABASE: wcorg_test
-        ports:
-          - 3306/tcp
-        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=5s --health-retries=3
-
     steps:
     - uses: actions/checkout@v4
 
@@ -74,26 +63,33 @@ jobs:
         sudo rm -f /var/lib/man-db/auto-update # https://github.com/actions/runner-images/issues/10977
         sudo apt-get update && sudo apt-get install -y subversion
 
-    - name: Set PHP version
+    - name: Set up PHP
       uses: shivammathur/setup-php@v2
       with:
         php-version: ${{ matrix.php-version }}
         coverage: none
         tools: composer:v2
       env:
-          COMPOSER_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-    - name: Start mysql service
-      run: sudo /etc/init.d/mysql start
+        COMPOSER_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
     - name: Install dependencies
       run: |
         rm composer.lock || true
         composer install
 
-    - name: Install WordPress
-      run: |
-        bash .docker/bin/install-wp-tests.sh wcorg_test root root 127.0.0.1 latest
+    - name: Setup DDEV
+      uses: ddev/github-action-setup-ddev@v1
+      with:
+        autostart: false
+
+    - name: Set PHP version
+      run: ddev config --php-version=${{ matrix.php-version }}
+
+    - name: Start DDEV
+      run: ddev start
+
+    - name: Install WP test suite
+      run: ddev exec bash .docker/bin/install-wp-tests.sh wcorg_test root root db latest
 
     - name: Running unit tests
-      run: ./public_html/wp-content/mu-plugins/vendor/bin/phpunit -c phpunit.xml.dist
+      run: ddev exec ./public_html/wp-content/mu-plugins/vendor/bin/phpunit -c phpunit.xml.dist
diff --git a/.gitignore b/.gitignore
index ffbd5f9501..ece43d13b1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,16 @@
 docker-compose.override.yaml
 
 
+#
+# DDEV
+#
+.ddev/.ddev-docker-compose-*
+.ddev/db_snapshots
+.ddev/.global_commands
+.ddev/.homeadditions
+.ddev/.sso-config
+
+
 #
 # Misc
 #
diff --git a/composer.json b/composer.json
index f5ad46ed73..e97ef87701 100644
--- a/composer.json
+++ b/composer.json
@@ -129,7 +129,6 @@
 		"wordpress-plugin/camptix-bd-payments": "1.2",
 		"wordpress-plugin/camptix-mercadopago": "1.0.6",
 		"wpackagist-plugin/camptix-pagseguro": "*",
-		"wpackagist-plugin/camptix-payfast-gateway": "*",
 		"wpackagist-plugin/camptix-trustcard": "*",
 		"wpackagist-plugin/camptix-trustpay": "*",
 		"wordpress-plugin/camptix-paystack": "1.0.0",
@@ -143,14 +142,11 @@
 		"wpackagist-plugin/liveblog": "*",
 		"wpackagist-plugin/public-post-preview": "*",
 		"wpackagist-plugin/pwa": "*",
-		"wpackagist-plugin/supportflow": "dev-trunk",
-		"wpackagist-plugin/tagregator": "dev-trunk",
 		"wpackagist-plugin/wordpress-importer": "*",
 		"wpackagist-plugin/wp-cldr": "*",
 		"wpackagist-plugin/wp-super-cache": "*",
 		"wordpress-meta/wporg-profiles-wp-activity-notifier": "1.1",
 		"wporg/wporg-mu-plugins": "dev-build",
-		"wpackagist-theme/p2": "*",
 		"wpackagist-theme/twentyten": "*",
 		"wpackagist-theme/twentytwentytwo": "*",
 		"wpackagist-theme/twentytwentythree": "*",
@@ -165,6 +161,7 @@
 		"test:watch:group": "phpunit-watcher watch --group=",
 		"_test:watch:fast_comment": "This can't use `@test:watch`, because that only works if `@` is the first character in the string. It can't manually call `composer run test:watch`, because that strips out extra arguments like `-- group=sunrise`. This must be manually kept in sync with the `test:watch` command.",
 		"test:watch:fast": "WP_TESTS_SKIP_INSTALL=1 phpunit-watcher watch < /dev/tty",
+		"test:ddev": "ddev exec ./public_html/wp-content/mu-plugins/vendor/bin/phpunit -c phpunit.xml.dist",
 		"test:db:reset": "/usr/bin/env php .docker/bin/reset-tests-database.php",
 		"test:coverage":  "php -d xdebug.mode=coverage public_html/wp-content/mu-plugins/vendor/bin/phpunit --coverage-html .phpunit/coverage-report",
 		"phpcs-changed": "BASE_REF=production php .github/bin/phpcs-branch.php ",
diff --git a/phpunit-bootstrap.php b/phpunit-bootstrap.php
index 1e9de559c9..4f8a2d8074 100644
--- a/phpunit-bootstrap.php
+++ b/phpunit-bootstrap.php
@@ -1,10 +1,18 @@
 <?php
 
+// Detect DDEV environment (runs inside /var/www/html).
+$is_ddev = str_starts_with( __DIR__, '/var/www/html' );
+
 // Require composer dependencies.
-if ( file_exists( __DIR__ . '/vendor/autoload.php' ) ) {
-	require_once __DIR__ . '/vendor/autoload.php';
+$vendor_autoload = $is_ddev
+	? '/var/www/html/vendor/autoload.php'
+	: __DIR__ . '/vendor/autoload.php';
+
+if ( file_exists( $vendor_autoload ) ) {
+	require_once $vendor_autoload;
 }
 
+const WORDCAMP_ENVIRONMENT  = 'local';
 const WORDCAMP_NETWORK_ID   = 1;
 const WORDCAMP_ROOT_BLOG_ID = 5;
 const EVENTS_NETWORK_ID     = 2;
@@ -14,14 +22,24 @@
 const SITE_ID_CURRENT_SITE  = WORDCAMP_NETWORK_ID;
 const BLOG_ID_CURRENT_SITE  = WORDCAMP_ROOT_BLOG_ID;
 
-define( 'WP_PLUGIN_DIR', __DIR__ . '/public_html/wp-content/plugins' );
-define( 'SUT_WP_CONTENT_DIR', __DIR__ . '/public_html/wp-content/' ); // WP_CONTENT_DIR will be in `WP_TESTS_DIR`.
-define( 'SUT_WPMU_PLUGIN_DIR', SUT_WP_CONTENT_DIR . '/mu-plugins' ); // WPMU_PLUGIN_DIR will be in `WP_TESTS_DIR`.
+if ( $is_ddev ) {
+	define( 'WP_PLUGIN_DIR', '/var/www/html/public_html/wp-content/plugins' );
+	define( 'SUT_WP_CONTENT_DIR', '/var/www/html/public_html/wp-content/' );
+} else {
+	define( 'WP_PLUGIN_DIR', __DIR__ . '/public_html/wp-content/plugins' );
+	define( 'SUT_WP_CONTENT_DIR', __DIR__ . '/public_html/wp-content/' ); // WP_CONTENT_DIR will be in `WP_TESTS_DIR`.
+}
+define( 'SUT_WPMU_PLUGIN_DIR', SUT_WP_CONTENT_DIR . 'mu-plugins' ); // WPMU_PLUGIN_DIR will be in `WP_TESTS_DIR`.
 
 $core_tests_directory = getenv( 'WP_TESTS_DIR' );
 
 if ( ! $core_tests_directory ) {
-	$core_tests_directory = rtrim( sys_get_temp_dir(), '/\\' ) . '/wp/wordpress-tests-lib';
+	if ( $is_ddev && is_dir( '/tmp/wp/wordpress-tests-lib' ) ) {
+		$core_tests_directory = '/tmp/wp/wordpress-tests-lib';
+	} else {
+		$core_tests_directory = rtrim( sys_get_temp_dir(), '/\\' ) . '/wp/wordpress-tests-lib';
+	}
+
 	// Necessary for the CampTix tests.
 	putenv( "WP_TESTS_DIR=$core_tests_directory" );
 }
diff --git a/public_html/wp-content/mu-plugins/0-aaa-constants.php b/public_html/wp-content/mu-plugins/0-aaa-constants.php
new file mode 100644
index 0000000000..b5a8966e15
--- /dev/null
+++ b/public_html/wp-content/mu-plugins/0-aaa-constants.php
@@ -0,0 +1,36 @@
+<?php
+/**
+ * Define fallback constants for environments where wp-config.php
+ * hasn't yet defined them.
+ *
+ * Some environments run `wp core install` before setting custom
+ * constants, so they aren't available when mu-plugins first load
+ * during installation. This file provides safe defaults so the
+ * mu-plugins don't cause fatal errors during that initial bootstrap.
+ *
+ * In production and Docker environments, all constants are already
+ * defined in wp-config.php, so this file is a no-op.
+ */
+
+$defaults = array(
+	'WORDCAMP_ENVIRONMENT'  => 'local',
+	'WORDCAMP_NETWORK_ID'   => 1,
+	'WORDCAMP_ROOT_BLOG_ID' => 5,
+	'EVENTS_NETWORK_ID'     => 2,
+	'EVENTS_ROOT_BLOG_ID'   => 47,
+	'CAMPUS_NETWORK_ID'     => 3,
+	'CAMPUS_ROOT_BLOG_ID'   => 47,
+	'SITE_ID_CURRENT_SITE'  => 1,
+	'BLOG_ID_CURRENT_SITE'  => 5,
+
+	// Multisite constants needed so WordPress loads the multisite
+	// function stack (get_site_meta, etc.) during initial install.
+	'MULTISITE'             => true,
+	'SUBDOMAIN_INSTALL'     => true,
+);
+
+foreach ( $defaults as $name => $value ) {
+	if ( ! defined( $name ) ) {
+		define( $name, $value );
+	}
+}
diff --git a/public_html/wp-content/mu-plugins/tests/test-sunrise-events.php b/public_html/wp-content/mu-plugins/tests/test-sunrise-events.php
index 65e7c00b42..2f192eb06e 100644
--- a/public_html/wp-content/mu-plugins/tests/test-sunrise-events.php
+++ b/public_html/wp-content/mu-plugins/tests/test-sunrise-events.php
@@ -26,6 +26,8 @@ class Test_Sunrise_Events extends WP_UnitTestCase {
 	 * @dataProvider data_get_redirect_url
 	 */
 	public function test_get_redirect_url( $request_uri, $expected_url ) {
+		$_SERVER['HTTP_HOST'] = 'events.wordpress.test';
+
 		$actual_url = get_redirect_url( $request_uri );
 
 		$this->assertSame( $expected_url, $actual_url );
diff --git a/public_html/wp-content/sunrise-events.php b/public_html/wp-content/sunrise-events.php
index 53176932b5..eec8482ac5 100644
--- a/public_html/wp-content/sunrise-events.php
+++ b/public_html/wp-content/sunrise-events.php
@@ -31,7 +31,7 @@ function main() {
  * Get the URL to redirect to, if any.
  */
 function get_redirect_url( string $request_uri ): string {
-	$domain       = 'events.wordpress.' . get_top_level_domain();
+	$domain       = strtolower( strtok( $_SERVER['HTTP_HOST'] ?? '', ':' ) );
 	$old_full_url = sprintf(
 		'https://%s/%s',
 		$domain,
@@ -68,8 +68,11 @@ function get_redirect_url( string $request_uri ): string {
 function set_network_and_site() {
 	global $current_site, $current_blog, $blog_id, $site_id, $domain, $path, $public;
 
+	$host       = strtolower( strtok( $_SERVER['HTTP_HOST'] ?? '', ':' ) );
+	$network_id = \WordCamp\Sunrise\get_domain_network_id( $host );
+
 	// Originally WP referred to networks as "sites" and sites as "blogs".
-	$current_site = WP_Network::get_instance( SITE_ID_CURRENT_SITE );
+	$current_site = WP_Network::get_instance( $network_id );
 	$site_id      = $current_site->id;
 	$path         = stripslashes( $_SERVER['REQUEST_URI'] );
 
@@ -80,7 +83,7 @@ function set_network_and_site() {
 
 		list( $path ) = explode( '?', $path );
 
-		$current_blog = get_site_by_path( DOMAIN_CURRENT_SITE, $path, 3 );
+		$current_blog = get_site_by_path( $host, $path, 3 );
 
 	} elseif (
 		CAMPUS_NETWORK_ID === $site_id &&
@@ -92,9 +95,9 @@ function set_network_and_site() {
 
 		list( $path ) = explode( '?', $path );
 
-		$current_blog = get_site_by_path( DOMAIN_CURRENT_SITE, $path, 2 );
+		$current_blog = get_site_by_path( $host, $path, 2 );
 	} else {
-		$current_blog = WP_Site::get_instance( BLOG_ID_CURRENT_SITE ); // The Root site constant defined in wp-config.php.
+		$current_blog = WP_Site::get_instance( $current_site->blog_id );
 	}
 
 	if ( ! $current_blog ) {
diff --git a/public_html/wp-content/sunrise-wordcamp.php b/public_html/wp-content/sunrise-wordcamp.php
index a1ddc3e202..b9b9fc3ca0 100644
--- a/public_html/wp-content/sunrise-wordcamp.php
+++ b/public_html/wp-content/sunrise-wordcamp.php
@@ -136,8 +136,11 @@ function ( array $settings ): array {
 function set_network_and_site( object $site ) {
 	global $current_site, $current_blog, $blog_id, $site_id, $domain, $path, $public;
 
+	$host       = strtolower( strtok( $_SERVER['HTTP_HOST'] ?? '', ':' ) );
+	$network_id = \WordCamp\Sunrise\get_domain_network_id( $host );
+
 	// Originally WP referred to networks as "sites" and sites as "blogs".
-	$current_site = WP_Network::get_instance( WORDCAMP_NETWORK_ID );
+	$current_site = WP_Network::get_instance( $network_id );
 	$site_id      = $current_site->id;
 	$path         = stripslashes( $_SERVER['REQUEST_URI'] );
 	$current_blog = WP_Site::get_instance( $site->blog_id );
diff --git a/public_html/wp-content/sunrise.php b/public_html/wp-content/sunrise.php
index 34427371e1..52656dd005 100644
--- a/public_html/wp-content/sunrise.php
+++ b/public_html/wp-content/sunrise.php
@@ -87,7 +87,10 @@
  * Load the sunrise file for the current network.
  */
 function load_network_sunrise() {
-	switch ( SITE_ID_CURRENT_SITE ) {
+	$host       = strtolower( strtok( $_SERVER['HTTP_HOST'] ?? '', ':' ) );
+	$network_id = get_domain_network_id( $host );
+
+	switch ( $network_id ) {
 		case CAMPUS_NETWORK_ID:
 			// Intentional Fall through. Load Events plugins for now.
 		case EVENTS_NETWORK_ID: