feat: Add option to disable early mode (v0.4.2)

- Add wp_prometheus_disable_early_mode option in admin settings
- Support WP_PROMETHEUS_DISABLE_EARLY_MODE environment variable
- Add Early Mode section in Metrics tab with status indicator
- Allow users to enable wp_prometheus_collect_metrics hook

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Admin/Settings.php

@@ -118,6 +118,12 @@ class Settings {
 			'sanitize_callback' => array( $this, 'sanitize_metrics' ),
 		) );
 
+		register_setting( 'wp_prometheus_metrics_settings', 'wp_prometheus_disable_early_mode', array(
+			'type'              => 'boolean',
+			'sanitize_callback' => 'rest_sanitize_boolean',
+			'default'           => false,
+		) );
+
 		// Auth token section.
 		add_settings_section(
 			'wp_prometheus_auth_section',
@@ -420,6 +426,66 @@ class Settings {
 			<span id="wp-prometheus-reset-spinner" class="spinner" style="float: none;"></span>
 		</p>
 		<div id="wp-prometheus-reset-message" style="display: none; margin-top: 10px;"></div>
+
+		<hr style="margin: 30px 0;">
+
+		<?php $this->render_early_mode_section(); ?>
+		<?php
+	}
+
+	/**
+	 * Render early mode section.
+	 *
+	 * @return void
+	 */
+	private function render_early_mode_section(): void {
+		$disabled       = get_option( 'wp_prometheus_disable_early_mode', false );
+		$env_override   = false !== getenv( 'WP_PROMETHEUS_DISABLE_EARLY_MODE' );
+		$early_active   = defined( 'WP_PROMETHEUS_EARLY_METRICS' ) && WP_PROMETHEUS_EARLY_METRICS;
+		?>
+		<h3><?php esc_html_e( 'Early Mode', 'wp-prometheus' ); ?></h3>
+		<p class="description">
+			<?php esc_html_e( 'Early mode intercepts /metrics requests before full WordPress initialization. This prevents memory exhaustion issues caused by some plugins (e.g., Twig-based themes/plugins) but disables the wp_prometheus_collect_metrics hook for custom metrics.', 'wp-prometheus' ); ?>
+		</p>
+
+		<?php if ( $env_override ) : ?>
+			<div class="notice notice-info inline" style="padding: 12px; margin: 15px 0;">
+				<strong><?php esc_html_e( 'Environment Override Active', 'wp-prometheus' ); ?></strong>
+				<p><?php esc_html_e( 'Early mode is configured via WP_PROMETHEUS_DISABLE_EARLY_MODE environment variable. Admin settings will be ignored.', 'wp-prometheus' ); ?></p>
+			</div>
+		<?php endif; ?>
+
+		<table class="form-table" role="presentation">
+			<tr>
+				<th scope="row"><?php esc_html_e( 'Disable Early Mode', 'wp-prometheus' ); ?></th>
+				<td>
+					<label>
+						<input type="checkbox" name="wp_prometheus_disable_early_mode" value="1"
+							<?php checked( $disabled ); ?>
+							<?php disabled( $env_override ); ?>>
+						<?php esc_html_e( 'Disable early metrics interception', 'wp-prometheus' ); ?>
+					</label>
+					<p class="description">
+						<?php esc_html_e( 'When disabled, metrics are collected through normal WordPress template loading. This enables the wp_prometheus_collect_metrics hook for custom metrics but may cause issues with some plugins.', 'wp-prometheus' ); ?>
+					</p>
+				</td>
+			</tr>
+			<tr>
+				<th scope="row"><?php esc_html_e( 'Current Status', 'wp-prometheus' ); ?></th>
+				<td>
+					<?php if ( $early_active ) : ?>
+						<span class="dashicons dashicons-yes-alt" style="color: green;"></span>
+						<?php esc_html_e( 'Early mode is active (this request was served via early interception)', 'wp-prometheus' ); ?>
+					<?php elseif ( $disabled || $env_override ) : ?>
+						<span class="dashicons dashicons-dismiss" style="color: gray;"></span>
+						<?php esc_html_e( 'Early mode is disabled', 'wp-prometheus' ); ?>
+					<?php else : ?>
+						<span class="dashicons dashicons-yes-alt" style="color: green;"></span>
+						<?php esc_html_e( 'Early mode is enabled (active for /metrics requests)', 'wp-prometheus' ); ?>
+					<?php endif; ?>
+				</td>
+			</tr>
+		</table>
 		<?php
 	}