fix: Separate settings groups to prevent cross-tab overwrites (v0.4.5)

Split Metrics sub-tab settings into separate WordPress option groups:
- wp_prometheus_endpoint_settings for auth token
- wp_prometheus_selection_settings for enabled metrics
- wp_prometheus_advanced_settings for isolated mode

This fixes the bug where saving from one sub-tab would clear settings
from other sub-tabs due to all settings sharing a single option group.

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

CHANGELOG.md

@@ -5,6 +5,65 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.4.5] - 2026-02-02
+
+### Fixed
+
+- Settings now persist correctly across Metrics sub-tabs
+- Auth token no longer gets cleared when saving from Selection sub-tab
+- Enabled metrics no longer get cleared when saving from Endpoint sub-tab
+- Isolated mode setting no longer gets cleared when saving from other sub-tabs
+
+### Changed
+
+- Split Metrics settings into separate WordPress option groups per sub-tab
+- Each sub-tab now uses its own settings group to prevent cross-tab overwrites
+
+## [0.4.4] - 2026-02-02
+
+### Added
+
+- Safe mode for metrics collection (default):
+  - Removes problematic content filters early
+  - Allows third-party plugins to register `wp_prometheus_collect_metrics` hooks
+  - Wraps custom hooks in output buffering and try-catch for protection
+- Isolated mode option for maximum compatibility:
+  - Outputs metrics before other plugins fully load
+  - Use only if Safe mode causes issues
+- `WP_PROMETHEUS_ISOLATED_MODE` environment variable support
+- Mode comparison table in admin settings
+
+### Changed
+
+- Replaced "early mode" with two clear modes: Safe (default) and Isolated
+- Custom metrics hooks now fire by default with protection against recursion
+- Filter removal now also includes `the_content_feed` and `comment_text`
+- Updated admin UI with clearer explanations of each mode
+
+### Fixed
+
+- Third-party plugins can now add custom metrics without memory issues
+- Twig-based plugins (like wp-fedistream) no longer cause recursion
+
+## [0.4.3] - 2026-02-02
+
+### Added
+
+- Sub-tabs navigation within Metrics tab (Endpoint, Selection, Runtime, Advanced)
+- Option to disable early mode in admin settings (Metrics → Advanced)
+- Support for `WP_PROMETHEUS_DISABLE_EARLY_MODE` environment variable
+- Early mode status display in settings
+
+### Fixed
+
+- Early mode setting now saves correctly (moved into form with proper settings group)
+
+### Changed
+
+- Reorganized Metrics tab into logical sub-sections for better usability
+- Early mode can now be disabled for users who need the `wp_prometheus_collect_metrics` hook
+- Updated translations with sub-tab and early mode strings (English and German)
+
 ## [0.4.1] - 2026-02-02
 
 ### Fixed

CLAUDE.md

@@ -291,6 +291,112 @@ add_action( 'wp_prometheus_collect_metrics', function( $collector ) {
 
 ## Session History
 
+### 2026-02-02 - Settings Persistence Fix (v0.4.5)
+
+- Fixed critical bug where settings would get cleared when saving from different Metrics sub-tabs
+- Root cause: All settings were registered under single `wp_prometheus_metrics_settings` group
+  - When saving from "Endpoint" sub-tab, only auth token was in POST data
+  - WordPress Settings API would process all registered settings in the group
+  - Missing fields (enabled_metrics, isolated_mode) would receive null/undefined
+  - Sanitize callbacks returned empty values, overwriting existing settings
+- Solution: Split into separate settings groups per sub-tab:
+  - `wp_prometheus_endpoint_settings` for auth token
+  - `wp_prometheus_selection_settings` for enabled metrics
+  - `wp_prometheus_advanced_settings` for isolated mode
+- **Key Learning**: WordPress Settings API and multiple forms
+  - When multiple forms share the same settings group, saving one form can clear settings from another
+  - Each form with `settings_fields()` should use a unique option group
+  - `register_setting()` group name must match `settings_fields()` group name
+
+### 2026-02-02 - Safe Mode & Custom Hooks Fix (v0.4.4)
+
+- Redesigned metrics collection to support both plugin compatibility AND custom metrics:
+  - **Safe Mode (default)**: Removes content filters early but lets WordPress load normally
+  - **Isolated Mode**: Legacy early mode that skips custom hooks entirely
+- Implementation:
+  - `WP_PROMETHEUS_METRICS_REQUEST` constant set for any /metrics request
+  - Content filters removed via `plugins_loaded` hook at priority 0
+  - Collector fires `wp_prometheus_collect_metrics` with protection (output buffering, try-catch)
+  - `wp_prometheus_isolated_mode` option replaces `wp_prometheus_disable_early_mode`
+  - `WP_PROMETHEUS_ISOLATED_MODE` environment variable for containerized deployments
+- Collector now wraps custom hooks in `fire_custom_metrics_hook()` method:
+  - Removes content filters again before hook (in case re-added)
+  - Uses output buffering to discard accidental output
+  - Catches exceptions to prevent breaking metrics output
+  - Logs errors when WP_DEBUG is enabled
+- Updated admin UI with mode comparison table
+- **Key Learning**: Hybrid approach for plugin compatibility
+  - The memory issue comes from content filter recursion, not just plugin loading
+  - Removing filters early (before any plugin can trigger them) prevents recursion
+  - Plugins still load and can register their `wp_prometheus_collect_metrics` hooks
+  - Hooks fire after filters are removed, in a protected context
+- **Key Learning**: Defense in depth for custom hooks
+  - Remove filters again right before hook fires (plugins may re-add them)
+  - Output buffering catches any echo/print from misbehaving plugins
+  - Try-catch prevents one broken plugin from breaking metrics entirely
+
+### 2026-02-02 - Sub-tabs & Early Mode Fix (v0.4.3)
+
+- Split Metrics tab into sub-tabs for better organization:
+  - **Endpoint**: Authentication token configuration
+  - **Selection**: Enable/disable individual metrics
+  - **Runtime**: Reset runtime metrics data
+  - **Advanced**: Early mode toggle and status
+- Fixed early mode setting not being saved (was outside form element)
+- Added CSS styling for horizontal sub-tab navigation
+- **Key Learning**: WordPress Settings API form structure
+  - Settings must be inside `<form action="options.php">` with `settings_fields()` call
+  - Each sub-tab needs its own form wrapper for proper saving
+  - Sub-tabs use URL query parameter (`subtab`) within the main tab
+- **Key Learning**: WordPress plugin versioning requires TWO updates
+  - Plugin header comment `Version: x.x.x` (line ~6) - used by WordPress admin
+  - PHP constant `WP_PROMETHEUS_VERSION` (line ~133) - used internally
+  - CI/CD checks both must match the git tag, causing release failures if mismatched
+
+### 2026-02-02 - Early Mode Toggle (v0.4.2)
+
+- Added option to disable early mode for users who need extensibility
+- Implementation:
+  - Added `wp_prometheus_disable_early_mode` WordPress option
+  - Added `WP_PROMETHEUS_DISABLE_EARLY_MODE` environment variable support
+  - Option check in `wp_prometheus_early_metrics_check()` before early interception
+  - Environment variable accepts `1`, `true`, `yes`, `on` (case-insensitive)
+- Admin UI in Metrics tab:
+  - "Early Mode" section with description of functionality
+  - Checkbox to disable early metrics interception
+  - Environment override notice when env var is set
+  - Current status indicator showing early mode state
+- **Key Learning**: Balancing compatibility vs extensibility
+  - Early mode fixes memory issues but disables `wp_prometheus_collect_metrics` hook
+  - Users with custom metrics need the hook, so early mode must be optional
+  - Default remains enabled (safe) with explicit opt-out for advanced users
+
+### 2026-02-02 - Plugin Compatibility Fix (v0.4.1)
+
+- Fixed memory exhaustion (1GB limit) when wp-fedistream (Twig-based) plugin is active
+- Root cause: Infinite recursion through WordPress hook system when content filters trigger Twig rendering
+- Solution: Early metrics endpoint interception before full WordPress initialization
+- Implementation changes:
+  - Added `wp_prometheus_early_metrics_check()` in bootstrap file (wp-prometheus.php)
+  - Checks REQUEST_URI for `/metrics` pattern before `plugins_loaded` fires
+  - Defines `WP_PROMETHEUS_EARLY_METRICS` constant to signal early mode
+  - Removes content filters (`the_content`, `the_excerpt`, `get_the_excerpt`, `the_title`)
+  - Collector skips `wp_prometheus_collect_metrics` action in early mode
+  - Changed MetricsEndpoint from `template_redirect` to `parse_request` hook
+- **Key Learning**: WordPress plugin loading order and hook timing
+  - Plugins load alphabetically, so wp-fedistream ('f') loads before wp-prometheus ('p')
+  - `template_redirect` fires too late - after themes and Twig initialize
+  - `parse_request` fires earlier but still after plugin files load
+  - Earliest interception point: top-level code in plugin bootstrap file
+- **Key Learning**: Content filter recursion in WordPress
+  - `get_the_excerpt()` internally triggers `apply_filters('the_content', ...)`
+  - This creates unexpected recursion vectors when Twig templates process content
+  - Solution: Remove all content-related filters before metrics collection
+- **Key Learning**: Isolating metrics collection from WordPress template system
+  - Use `remove_all_filters()` to clear problematic filter chains
+  - Skip extensibility hooks (`do_action`) when in isolated early mode
+  - Exit immediately after output to prevent further WordPress processing
+
 ### 2026-02-02 - Persistent Storage (v0.4.0)
 
 - Added persistent storage support for metrics:

assets/css/admin.css

@@ -9,6 +9,61 @@
     margin-top: 20px;
 }
 
+/* Sub-tabs navigation */
+.wp-prometheus-subtabs {
+    margin-top: 15px;
+}
+
+.wp-prometheus-subtab-nav {
+    display: flex;
+    margin: 0;
+    padding: 0;
+    list-style: none;
+    border-bottom: 1px solid #c3c4c7;
+}
+
+.wp-prometheus-subtab-item {
+    margin: 0;
+    padding: 0;
+}
+
+.wp-prometheus-subtab-item a {
+    display: block;
+    padding: 8px 16px;
+    text-decoration: none;
+    color: #50575e;
+    border: 1px solid transparent;
+    border-bottom: none;
+    margin-bottom: -1px;
+    background: transparent;
+    font-size: 13px;
+    font-weight: 400;
+}
+
+.wp-prometheus-subtab-item a:hover {
+    color: #2271b1;
+    background: #f6f7f7;
+}
+
+.wp-prometheus-subtab-item.active a {
+    color: #1d2327;
+    background: #fff;
+    border-color: #c3c4c7;
+    border-bottom-color: #fff;
+    font-weight: 600;
+}
+
+.wp-prometheus-subtab-content {
+    background: #fff;
+    border: 1px solid #c3c4c7;
+    border-top: none;
+    padding: 20px;
+}
+
+.wp-prometheus-subtab-content h3:first-child {
+    margin-top: 0;
+}
+
 /* License status box */
 .wp-prometheus-license-status {
     margin: 15px 0;

languages/wp-prometheus-de_CH.po

@@ -3,7 +3,7 @@
 # This file is distributed under the GPL v2 or later.
 msgid ""
 msgstr ""
-"Project-Id-Version: WP Prometheus 0.4.0\n"
+"Project-Id-Version: WP Prometheus 0.4.2\n"
 "Report-Msgid-Bugs-To: https://src.bundespruefstelle.ch/magdev/wp-prometheus/issues\n"
 "POT-Creation-Date: 2026-02-02T00:00:00+00:00\n"
 "PO-Revision-Date: 2026-02-02T00:00:00+00:00\n"
@@ -879,3 +879,71 @@ msgstr "APCu funktioniert. Speicher: %s belegt."
 #: src/Metrics/StorageFactory.php
 msgid "APCu fetch operation returned unexpected value."
 msgstr "APCu-Abrufoperation hat unerwarteten Wert zurueckgegeben."
+
+#: src/Admin/Settings.php
+msgid "Early Mode"
+msgstr "Fruehzeitiger Modus"
+
+#: src/Admin/Settings.php
+msgid "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."
+msgstr "Der fruehzeitige Modus faengt /metrics-Anfragen vor der vollstaendigen WordPress-Initialisierung ab. Dies verhindert Speichererschoepfungsprobleme, die durch einige Plugins verursacht werden (z.B. Twig-basierte Themes/Plugins), deaktiviert jedoch den wp_prometheus_collect_metrics-Hook fuer benutzerdefinierte Metriken."
+
+#: src/Admin/Settings.php
+msgid "Early mode is configured via WP_PROMETHEUS_DISABLE_EARLY_MODE environment variable. Admin settings will be ignored."
+msgstr "Der fruehzeitige Modus ist ueber die Umgebungsvariable WP_PROMETHEUS_DISABLE_EARLY_MODE konfiguriert. Admin-Einstellungen werden ignoriert."
+
+#: src/Admin/Settings.php
+msgid "Disable Early Mode"
+msgstr "Fruehzeitigen Modus deaktivieren"
+
+#: src/Admin/Settings.php
+msgid "Disable early metrics interception"
+msgstr "Fruehzeitige Metriken-Abfangung deaktivieren"
+
+#: src/Admin/Settings.php
+msgid "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."
+msgstr "Wenn deaktiviert, werden Metriken ueber das normale WordPress-Template-Laden erfasst. Dies aktiviert den wp_prometheus_collect_metrics-Hook fuer benutzerdefinierte Metriken, kann jedoch Probleme mit einigen Plugins verursachen."
+
+#: src/Admin/Settings.php
+msgid "Early mode is active (this request was served via early interception)"
+msgstr "Fruehzeitiger Modus ist aktiv (diese Anfrage wurde ueber fruehzeitige Abfangung verarbeitet)"
+
+#: src/Admin/Settings.php
+msgid "Early mode is disabled"
+msgstr "Fruehzeitiger Modus ist deaktiviert"
+
+#: src/Admin/Settings.php
+msgid "Early mode is enabled (active for /metrics requests)"
+msgstr "Fruehzeitiger Modus ist aktiviert (aktiv fuer /metrics-Anfragen)"
+
+#: src/Admin/Settings.php
+msgid "Clear all accumulated runtime metric data (HTTP requests, database queries). This is useful for testing or starting fresh."
+msgstr "Alle gesammelten Laufzeit-Metrikdaten loeschen (HTTP-Anfragen, Datenbank-Abfragen). Dies ist nuetzlich zum Testen oder fuer einen Neuanfang."
+
+#: src/Admin/Settings.php
+msgid "Endpoint"
+msgstr "Endpunkt"
+
+#: src/Admin/Settings.php
+msgid "Selection"
+msgstr "Auswahl"
+
+#: src/Admin/Settings.php
+msgid "Runtime"
+msgstr "Laufzeit"
+
+#: src/Admin/Settings.php
+msgid "Advanced"
+msgstr "Erweitert"
+
+#: src/Admin/Settings.php
+msgid "Runtime Metrics Management"
+msgstr "Laufzeit-Metriken Verwaltung"
+
+#: src/Admin/Settings.php
+msgid "Runtime metrics track HTTP requests and database queries across requests. Use this section to manage accumulated data."
+msgstr "Laufzeit-Metriken erfassen HTTP-Anfragen und Datenbank-Abfragen ueber mehrere Anfragen hinweg. Verwenden Sie diesen Bereich zur Verwaltung der gesammelten Daten."
+
+#: src/Admin/Settings.php
+msgid "Reset Data"
+msgstr "Daten zuruecksetzen"

languages/wp-prometheus.pot

@@ -2,7 +2,7 @@
 # This file is distributed under the GPL v2 or later.
 msgid ""
 msgstr ""
-"Project-Id-Version: WP Prometheus 0.4.0\n"
+"Project-Id-Version: WP Prometheus 0.4.2\n"
 "Report-Msgid-Bugs-To: https://src.bundespruefstelle.ch/magdev/wp-prometheus/issues\n"
 "POT-Creation-Date: 2026-02-02T00:00:00+00:00\n"
 "MIME-Version: 1.0\n"
@@ -876,3 +876,71 @@ msgstr ""
 #: src/Metrics/StorageFactory.php
 msgid "APCu fetch operation returned unexpected value."
 msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Early Mode"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "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."
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Early mode is configured via WP_PROMETHEUS_DISABLE_EARLY_MODE environment variable. Admin settings will be ignored."
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Disable Early Mode"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Disable early metrics interception"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "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."
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Early mode is active (this request was served via early interception)"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Early mode is disabled"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Early mode is enabled (active for /metrics requests)"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Clear all accumulated runtime metric data (HTTP requests, database queries). This is useful for testing or starting fresh."
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Endpoint"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Selection"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Runtime"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Advanced"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Runtime Metrics Management"
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Runtime metrics track HTTP requests and database queries across requests. Use this section to manage accumulated data."
+msgstr ""
+
+#: src/Admin/Settings.php
+msgid "Reset Data"
+msgstr ""

src/Admin/Settings.php

@@ -107,17 +107,25 @@ class Settings {
 	 * @return void
 	 */
 	public function register_settings(): void {
-		// Register settings for metrics tab.
+		// Register settings for endpoint sub-tab.
-		register_setting( 'wp_prometheus_metrics_settings', 'wp_prometheus_auth_token', array(
+		register_setting( 'wp_prometheus_endpoint_settings', 'wp_prometheus_auth_token', array(
 			'type'              => 'string',
 			'sanitize_callback' => 'sanitize_text_field',
 		) );
 
-		register_setting( 'wp_prometheus_metrics_settings', 'wp_prometheus_enabled_metrics', array(
+		// Register settings for selection sub-tab.
+		register_setting( 'wp_prometheus_selection_settings', 'wp_prometheus_enabled_metrics', array(
 			'type'              => 'array',
 			'sanitize_callback' => array( $this, 'sanitize_metrics' ),
 		) );
 
+		// Register settings for advanced sub-tab.
+		register_setting( 'wp_prometheus_advanced_settings', 'wp_prometheus_isolated_mode', array(
+			'type'              => 'boolean',
+			'sanitize_callback' => 'rest_sanitize_boolean',
+			'default'           => false,
+		) );
+
 		// Auth token section.
 		add_settings_section(
 			'wp_prometheus_auth_section',
@@ -394,32 +402,261 @@ class Settings {
 		<?php
 	}
 
+	/**
+	 * Get metrics sub-tabs.
+	 *
+	 * @return array
+	 */
+	private function get_metrics_subtabs(): array {
+		return array(
+			'endpoint'  => __( 'Endpoint', 'wp-prometheus' ),
+			'selection' => __( 'Selection', 'wp-prometheus' ),
+			'runtime'   => __( 'Runtime', 'wp-prometheus' ),
+			'advanced'  => __( 'Advanced', 'wp-prometheus' ),
+		);
+	}
+
+	/**
+	 * Get current metrics sub-tab.
+	 *
+	 * @return string
+	 */
+	private function get_current_metrics_subtab(): string {
+		$subtab  = isset( $_GET['subtab'] ) ? sanitize_key( $_GET['subtab'] ) : 'endpoint';
+		$subtabs = $this->get_metrics_subtabs();
+		return array_key_exists( $subtab, $subtabs ) ? $subtab : 'endpoint';
+	}
+
 	/**
 	 * Render metrics tab content.
 	 *
 	 * @return void
 	 */
 	private function render_metrics_tab(): void {
+		$subtabs         = $this->get_metrics_subtabs();
+		$current_subtab  = $this->get_current_metrics_subtab();
+		?>
+		<div class="wp-prometheus-subtabs">
+			<ul class="wp-prometheus-subtab-nav">
+				<?php foreach ( $subtabs as $subtab_id => $subtab_name ) : ?>
+					<?php
+					$subtab_url = add_query_arg(
+						array(
+							'page'   => 'wp-prometheus',
+							'tab'    => 'metrics',
+							'subtab' => $subtab_id,
+						),
+						admin_url( 'options-general.php' )
+					);
+					$active_class = ( $current_subtab === $subtab_id ) ? ' active' : '';
+					?>
+					<li class="wp-prometheus-subtab-item<?php echo esc_attr( $active_class ); ?>">
+						<a href="<?php echo esc_url( $subtab_url ); ?>"><?php echo esc_html( $subtab_name ); ?></a>
+					</li>
+				<?php endforeach; ?>
+			</ul>
+
+			<div class="wp-prometheus-subtab-content">
+				<?php
+				switch ( $current_subtab ) {
+					case 'endpoint':
+						$this->render_metrics_endpoint_subtab();
+						break;
+					case 'selection':
+						$this->render_metrics_selection_subtab();
+						break;
+					case 'runtime':
+						$this->render_metrics_runtime_subtab();
+						break;
+					case 'advanced':
+						$this->render_metrics_advanced_subtab();
+						break;
+				}
+				?>
+			</div>
+		</div>
+		<?php
+	}
+
+	/**
+	 * Render metrics endpoint sub-tab.
+	 *
+	 * @return void
+	 */
+	private function render_metrics_endpoint_subtab(): void {
 		?>
 		<form method="post" action="options.php">
-			<?php
+			<?php settings_fields( 'wp_prometheus_endpoint_settings' ); ?>
-			settings_fields( 'wp_prometheus_metrics_settings' );
+
-			do_settings_sections( 'wp-prometheus-metrics' );
+			<h3><?php esc_html_e( 'Authentication', 'wp-prometheus' ); ?></h3>
-			submit_button();
+			<p class="description"><?php esc_html_e( 'Configure authentication for the /metrics endpoint.', 'wp-prometheus' ); ?></p>
-			?>
+
+			<table class="form-table" role="presentation">
+				<tr>
+					<th scope="row">
+						<label for="wp_prometheus_auth_token"><?php esc_html_e( 'Auth Token', 'wp-prometheus' ); ?></label>
+					</th>
+					<td>
+						<?php $this->render_auth_token_field(); ?>
+					</td>
+				</tr>
+			</table>
+
+			<?php submit_button(); ?>
 		</form>
+		<?php
+	}
 
-		<hr style="margin: 30px 0;">
+	/**
+	 * Render metrics selection sub-tab.
+	 *
+	 * @return void
+	 */
+	private function render_metrics_selection_subtab(): void {
+		?>
+		<form method="post" action="options.php">
+			<?php settings_fields( 'wp_prometheus_selection_settings' ); ?>
 
-		<h3><?php esc_html_e( 'Reset Runtime Metrics', 'wp-prometheus' ); ?></h3>
+			<h3><?php esc_html_e( 'Enabled Metrics', 'wp-prometheus' ); ?></h3>
-		<p class="description"><?php esc_html_e( 'Clear all accumulated runtime metric data (HTTP requests, database queries). This is useful for testing or starting fresh.', 'wp-prometheus' ); ?></p>
+			<p class="description"><?php esc_html_e( 'Select which metrics to expose on the /metrics endpoint.', 'wp-prometheus' ); ?></p>
-		<p>
+
-			<button type="button" id="wp-prometheus-reset-runtime" class="button button-secondary">
+			<table class="form-table" role="presentation">
-				<?php esc_html_e( 'Reset Runtime Metrics', 'wp-prometheus' ); ?>
+				<tr>
-			</button>
+					<th scope="row"><?php esc_html_e( 'Select Metrics', 'wp-prometheus' ); ?></th>
-			<span id="wp-prometheus-reset-spinner" class="spinner" style="float: none;"></span>
+					<td>
-		</p>
+						<?php $this->render_enabled_metrics_field(); ?>
-		<div id="wp-prometheus-reset-message" style="display: none; margin-top: 10px;"></div>
+					</td>
+				</tr>
+			</table>
+
+			<?php submit_button(); ?>
+		</form>
+		<?php
+	}
+
+	/**
+	 * Render metrics runtime sub-tab.
+	 *
+	 * @return void
+	 */
+	private function render_metrics_runtime_subtab(): void {
+		?>
+		<h3><?php esc_html_e( 'Runtime Metrics Management', 'wp-prometheus' ); ?></h3>
+		<p class="description"><?php esc_html_e( 'Runtime metrics track HTTP requests and database queries across requests. Use this section to manage accumulated data.', 'wp-prometheus' ); ?></p>
+
+		<table class="form-table" role="presentation">
+			<tr>
+				<th scope="row"><?php esc_html_e( 'Reset Data', 'wp-prometheus' ); ?></th>
+				<td>
+					<p class="description" style="margin-bottom: 10px;">
+						<?php esc_html_e( 'Clear all accumulated runtime metric data (HTTP requests, database queries). This is useful for testing or starting fresh.', 'wp-prometheus' ); ?>
+					</p>
+					<button type="button" id="wp-prometheus-reset-runtime" class="button button-secondary">
+						<?php esc_html_e( 'Reset Runtime Metrics', 'wp-prometheus' ); ?>
+					</button>
+					<span id="wp-prometheus-reset-spinner" class="spinner" style="float: none;"></span>
+					<div id="wp-prometheus-reset-message" style="display: none; margin-top: 10px;"></div>
+				</td>
+			</tr>
+		</table>
+		<?php
+	}
+
+	/**
+	 * Render metrics advanced sub-tab.
+	 *
+	 * @return void
+	 */
+	private function render_metrics_advanced_subtab(): void {
+		$isolated_mode = get_option( 'wp_prometheus_isolated_mode', false );
+		$env_override  = false !== getenv( 'WP_PROMETHEUS_ISOLATED_MODE' );
+		$is_metrics_request = defined( 'WP_PROMETHEUS_METRICS_REQUEST' ) && WP_PROMETHEUS_METRICS_REQUEST;
+		$is_isolated   = defined( 'WP_PROMETHEUS_ISOLATED_MODE' ) && WP_PROMETHEUS_ISOLATED_MODE;
+		?>
+		<form method="post" action="options.php">
+			<?php settings_fields( 'wp_prometheus_advanced_settings' ); ?>
+
+			<h3><?php esc_html_e( 'Metrics Collection Mode', 'wp-prometheus' ); ?></h3>
+
+			<div class="notice notice-info inline" style="padding: 12px; margin: 15px 0;">
+				<p><strong><?php esc_html_e( 'Safe Mode (Default)', 'wp-prometheus' ); ?></strong></p>
+				<p><?php esc_html_e( 'Content filters are removed early to prevent memory issues with Twig-based plugins, but WordPress loads normally. Third-party plugins can add custom metrics via the wp_prometheus_collect_metrics hook.', 'wp-prometheus' ); ?></p>
+			</div>
+
+			<?php if ( $env_override ) : ?>
+				<div class="notice notice-warning inline" style="padding: 12px; margin: 15px 0;">
+					<strong><?php esc_html_e( 'Environment Override Active', 'wp-prometheus' ); ?></strong>
+					<p><?php esc_html_e( 'Mode is configured via WP_PROMETHEUS_ISOLATED_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( 'Isolated Mode', 'wp-prometheus' ); ?></th>
+					<td>
+						<label>
+							<input type="checkbox" name="wp_prometheus_isolated_mode" value="1"
+								<?php checked( $isolated_mode ); ?>
+								<?php disabled( $env_override ); ?>>
+							<?php esc_html_e( 'Enable isolated mode', 'wp-prometheus' ); ?>
+						</label>
+						<p class="description">
+							<?php esc_html_e( 'Isolated mode outputs metrics immediately before other plugins fully load. This provides maximum isolation but disables the wp_prometheus_collect_metrics hook. Use this only if you experience issues with Safe Mode.', 'wp-prometheus' ); ?>
+						</p>
+					</td>
+				</tr>
+				<tr>
+					<th scope="row"><?php esc_html_e( 'Current Status', 'wp-prometheus' ); ?></th>
+					<td>
+						<?php if ( $is_isolated ) : ?>
+							<span class="dashicons dashicons-lock" style="color: orange;"></span>
+							<?php esc_html_e( 'Isolated mode active - custom hooks are disabled', 'wp-prometheus' ); ?>
+						<?php elseif ( $is_metrics_request ) : ?>
+							<span class="dashicons dashicons-yes-alt" style="color: green;"></span>
+							<?php esc_html_e( 'Safe mode active - custom hooks enabled with filter protection', 'wp-prometheus' ); ?>
+						<?php elseif ( $isolated_mode ) : ?>
+							<span class="dashicons dashicons-lock" style="color: orange;"></span>
+							<?php esc_html_e( 'Isolated mode enabled (active for /metrics requests)', 'wp-prometheus' ); ?>
+						<?php else : ?>
+							<span class="dashicons dashicons-yes-alt" style="color: green;"></span>
+							<?php esc_html_e( 'Safe mode enabled (default) - custom hooks with filter protection', 'wp-prometheus' ); ?>
+						<?php endif; ?>
+					</td>
+				</tr>
+			</table>
+
+			<hr style="margin: 20px 0;">
+
+			<h4><?php esc_html_e( 'Mode Comparison', 'wp-prometheus' ); ?></h4>
+			<table class="widefat striped" style="max-width: 700px;">
+				<thead>
+					<tr>
+						<th><?php esc_html_e( 'Feature', 'wp-prometheus' ); ?></th>
+						<th><?php esc_html_e( 'Safe Mode', 'wp-prometheus' ); ?></th>
+						<th><?php esc_html_e( 'Isolated Mode', 'wp-prometheus' ); ?></th>
+					</tr>
+				</thead>
+				<tbody>
+					<tr>
+						<td><?php esc_html_e( 'Custom metrics hook', 'wp-prometheus' ); ?></td>
+						<td><span class="dashicons dashicons-yes" style="color: green;"></span></td>
+						<td><span class="dashicons dashicons-no" style="color: red;"></span></td>
+					</tr>
+					<tr>
+						<td><?php esc_html_e( 'Plugin compatibility', 'wp-prometheus' ); ?></td>
+						<td><?php esc_html_e( 'High', 'wp-prometheus' ); ?></td>
+						<td><?php esc_html_e( 'Maximum', 'wp-prometheus' ); ?></td>
+					</tr>
+					<tr>
+						<td><?php esc_html_e( 'Memory usage', 'wp-prometheus' ); ?></td>
+						<td><?php esc_html_e( 'Normal', 'wp-prometheus' ); ?></td>
+						<td><?php esc_html_e( 'Minimal', 'wp-prometheus' ); ?></td>
+					</tr>
+				</tbody>
+			</table>
+
+			<?php submit_button(); ?>
+		</form>
 		<?php
 	}
 

src/Metrics/Collector.php

@@ -121,14 +121,62 @@ class Collector {
         /**
          * Fires after default metrics are collected.
          *
-         * Skip in early metrics mode to avoid triggering third-party hooks
+         * In isolated mode, skip custom hooks to avoid any potential issues.
-         * that may cause recursion issues (e.g., Twig-based plugins).
+         * In safe mode (default), fire hooks with protection against recursion.
          *
          * @param Collector $collector The metrics collector instance.
          */
-        if ( ! defined( 'WP_PROMETHEUS_EARLY_METRICS' ) || ! WP_PROMETHEUS_EARLY_METRICS ) {
+        if ( defined( 'WP_PROMETHEUS_ISOLATED_MODE' ) && WP_PROMETHEUS_ISOLATED_MODE ) {
-            do_action( 'wp_prometheus_collect_metrics', $this );
+            // Isolated mode: skip all third-party hooks for maximum safety.
+            return;
         }
+
+        // Safe mode: fire custom hooks with protection.
+        $this->fire_custom_metrics_hook();
+    }
+
+    /**
+     * Fire custom metrics hook with protection against recursion.
+     *
+     * Removes potentially problematic filters, uses output buffering,
+     * and catches any errors from third-party plugins.
+     *
+     * @return void
+     */
+    private function fire_custom_metrics_hook(): void {
+        // Remove content filters again (in case any plugin re-added them).
+        if ( function_exists( 'wp_prometheus_remove_content_filters' ) ) {
+            wp_prometheus_remove_content_filters();
+        } else {
+            // Fallback if function doesn't exist.
+            remove_all_filters( 'the_content' );
+            remove_all_filters( 'the_excerpt' );
+            remove_all_filters( 'get_the_excerpt' );
+            remove_all_filters( 'the_title' );
+        }
+
+        // Use output buffering to prevent any accidental output from plugins.
+        ob_start();
+
+        try {
+            /**
+             * Fires after default metrics are collected.
+             *
+             * Third-party plugins can use this hook to add custom metrics.
+             *
+             * @param Collector $collector The metrics collector instance.
+             */
+            do_action( 'wp_prometheus_collect_metrics', $this );
+        } catch ( \Throwable $e ) {
+            // Log the error but don't let it break metrics output.
+            if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
+                // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+                error_log( 'WP Prometheus: Error in custom metrics hook: ' . $e->getMessage() );
+            }
+        }
+
+        // Discard any output from plugins.
+        ob_end_clean();
     }
 
     /**

wp-prometheus.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP Prometheus
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-prometheus
  * Description: Prometheus metrics endpoint for WordPress with extensible hooks for custom metrics.
- * Version: 0.4.1
+ * Version: 0.4.5
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -22,11 +22,16 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 /**
- * Early metrics endpoint handler.
+ * Early metrics request detection.
  *
- * Intercepts /metrics requests before full WordPress initialization to avoid
+ * Detects /metrics requests early and removes problematic content filters
- * conflicts with other plugins that may cause issues during template loading.
+ * to prevent recursion issues with Twig-based plugins. Unlike the previous
- * This runs at plugin load time, before plugins_loaded hook.
+ * "early mode", this allows WordPress to continue loading so that third-party
+ * plugins can register their wp_prometheus_collect_metrics hooks.
+ *
+ * Two modes are available:
+ * - Safe mode (default): Removes filters early, lets WP load, fires custom hooks
+ * - Isolated mode: Outputs metrics immediately without custom hooks (legacy early mode)
  */
 function wp_prometheus_early_metrics_check(): void {
     // Only handle /metrics requests.
@@ -37,6 +42,58 @@ function wp_prometheus_early_metrics_check(): void {
         return;
     }
 
+    // Set flag to indicate we're handling a metrics request.
+    define( 'WP_PROMETHEUS_METRICS_REQUEST', true );
+
+    // Check if isolated mode is enabled via environment variable.
+    $env_isolated = getenv( 'WP_PROMETHEUS_ISOLATED_MODE' );
+    $isolated_mode = false !== $env_isolated && in_array( strtolower( $env_isolated ), array( '1', 'true', 'yes', 'on' ), true );
+
+    // Check if isolated mode is enabled via option (legacy "early mode" setting).
+    if ( ! $isolated_mode && ! get_option( 'wp_prometheus_disable_early_mode', false ) ) {
+        // Check for legacy isolated mode option.
+        $isolated_mode = (bool) get_option( 'wp_prometheus_isolated_mode', false );
+    }
+
+    // Remove all content filters immediately to prevent recursion with Twig-based plugins.
+    // This is done for BOTH safe mode and isolated mode.
+    add_action( 'plugins_loaded', 'wp_prometheus_remove_content_filters', 0 );
+
+    // Also remove filters now in case they were added by mu-plugins.
+    wp_prometheus_remove_content_filters();
+
+    // If isolated mode is enabled, handle metrics immediately without waiting for plugins.
+    if ( $isolated_mode ) {
+        wp_prometheus_isolated_metrics_handler();
+    }
+}
+
+/**
+ * Remove content filters that can cause recursion.
+ *
+ * Called early during metrics requests to prevent infinite loops
+ * with Twig-based plugins that hook into content filters.
+ *
+ * @return void
+ */
+function wp_prometheus_remove_content_filters(): void {
+    remove_all_filters( 'the_content' );
+    remove_all_filters( 'the_excerpt' );
+    remove_all_filters( 'get_the_excerpt' );
+    remove_all_filters( 'the_title' );
+    remove_all_filters( 'the_content_feed' );
+    remove_all_filters( 'comment_text' );
+}
+
+/**
+ * Handle metrics in isolated mode (no custom hooks).
+ *
+ * This is the legacy "early mode" that outputs metrics immediately
+ * without allowing third-party plugins to add custom metrics.
+ *
+ * @return void
+ */
+function wp_prometheus_isolated_metrics_handler(): void {
     // Check if autoloader exists.
     $autoloader = __DIR__ . '/vendor/autoload.php';
     if ( ! file_exists( $autoloader ) ) {
@@ -87,14 +144,8 @@ function wp_prometheus_early_metrics_check(): void {
         exit;
     }
 
-    // Set flag to indicate early metrics mode - Collector will skip extensibility hooks.
+    // Set flag to indicate isolated mode - Collector will skip extensibility hooks.
-    define( 'WP_PROMETHEUS_EARLY_METRICS', true );
+    define( 'WP_PROMETHEUS_ISOLATED_MODE', true );
-
-    // Remove all content filters to prevent recursion with Twig-based plugins.
-    remove_all_filters( 'the_content' );
-    remove_all_filters( 'the_excerpt' );
-    remove_all_filters( 'get_the_excerpt' );
-    remove_all_filters( 'the_title' );
 
     // Output metrics and exit immediately.
     $collector = new \Magdev\WpPrometheus\Metrics\Collector();
@@ -118,7 +169,7 @@ wp_prometheus_early_metrics_check();
  *
  * @var string
  */
-define( 'WP_PROMETHEUS_VERSION', '0.4.1' );
+define( 'WP_PROMETHEUS_VERSION', '0.4.5' );
 
 /**
  * Plugin file path.