perf: color variation CSS transient caching and Twig auto_reload fix (v1.0.9)

- functions.php: cache wp_bootstrap_variation_colors() output in a 24-hour
  transient keyed by md5(get_stylesheet()); invalidate on switch_theme and
  save_post_wp_global_styles so Design Editor changes apply immediately
- TwigService.php: change auto_reload from hardcoded true to WP_DEBUG so
  Twig stops stat()-ing compiled template files on every production request

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 All notable changes to this project will be documented in this file.
 
+## [1.0.9] - 2026-02-19
+
+### Performance
+
+- **Color variation CSS transient caching** (`functions.php`): `wp_bootstrap_variation_colors()` now caches the generated inline CSS in a 24-hour WordPress transient keyed by `wp_bootstrap_variation_css_` + an MD5 of the active stylesheet slug. Previously the palette iteration and CSS string building ran on every frontend page load. The transient is immediately invalidated on `switch_theme` and `save_post_wp_global_styles`, so changes made via the Design Editor are reflected instantly.
+- **Twig template recompilation gated behind `WP_DEBUG`** (`inc/Twig/TwigService.php`): `auto_reload` in the Twig `Environment` constructor was hardcoded to `true`, causing Twig to stat every compiled template file on every request to check for source changes. Changed to `WP_DEBUG` so template recompilation only occurs during development. In production (`WP_DEBUG = false`) compiled Twig templates are served from cache without filesystem mtime checks.
+
 ## [1.0.8] - 2026-02-19
 
 ### Security

CLAUDE.md

@@ -34,7 +34,7 @@ This project is proudly **"vibe-coded"** using Claude.AI - the entire codebase w
 
 **Note for AI Assistants:** Clean this section after the specific features are done or new releases are made. Effective changes are tracked in `CHANGELOG.md`. Do not add completed versions here - document them in the Session History section at the end of this file.
 
-Current version is **v1.0.5**. See `PLAN.md` for details.
+Current version is **v1.0.9**. See `PLAN.md` for details.
 
 ## Technical Stack
 
@@ -211,6 +211,22 @@ Build steps (in order):
 
 ## Session History
 
+### Session 15 — v1.0.9 Performance Optimization (2026-02-19)
+
+**Completed:** Two targeted performance fixes for production environments.
+
+**Changes made:**
+
+- **Color variation CSS transient caching** (`functions.php`): `wp_bootstrap_variation_colors()` now caches the generated Bootstrap CSS variable overrides in a 24-hour transient keyed by `wp_bootstrap_variation_css_` + `md5(get_stylesheet())`. Previously the palette loop and CSS string building executed on every frontend request. Transient is invalidated on `switch_theme` and `save_post_wp_global_styles` hooks so Design Editor changes apply immediately.
+- **Twig `auto_reload` gated behind `WP_DEBUG`** (`inc/Twig/TwigService.php`): Hardcoded `auto_reload => true` caused Twig to `stat()` each compiled template file on every request to detect source file changes. Changed to `auto_reload => WP_DEBUG` so stat checks only occur during development. In production, compiled templates are served from cache unconditionally.
+
+**Files modified:**
+
+- `functions.php` — transient caching and invalidation for variation CSS
+- `inc/Twig/TwigService.php` — `auto_reload => WP_DEBUG`
+- `style.css` — version bump to 1.0.9
+- `CHANGELOG.md` — v1.0.9 entry
+
 ### Session 14 — v1.0.8 Security Audit & Hardening (2026-02-19)
 
 **Completed:** Comprehensive OWASP-aligned security audit. Two parallel background agents reviewed all PHP (functions.php, ContextBuilder, NavWalker, TemplateController, TwigService, all patterns) and JavaScript/Twig templates. Four targeted security fixes applied.

functions.php

@@ -175,6 +175,17 @@ add_action( 'wp_enqueue_scripts', 'wp_bootstrap_rtl_styles', 20 );
  */
 if ( ! function_exists( 'wp_bootstrap_variation_colors' ) ) :
     function wp_bootstrap_variation_colors() {
+        $transient_key = 'wp_bootstrap_variation_css_' . md5( get_stylesheet() );
+        $cached_css    = get_transient( $transient_key );
+
+        if ( false !== $cached_css ) {
+            // '' means default palette (no inline CSS needed); non-empty string is the computed CSS.
+            if ( '' !== $cached_css ) {
+                wp_add_inline_style( 'wp-bootstrap-style', $cached_css );
+            }
+            return;
+        }
+
         // Read the theme origin palette — this contains the base theme.json
         // colors merged with the active style variation (if any).
         $theme_palette = wp_get_global_settings( array( 'color', 'palette', 'theme' ) );
@@ -205,10 +216,12 @@ if ( ! function_exists( 'wp_bootstrap_variation_colors' ) ) :
 
         // No variation active — let Bootstrap's compiled CSS handle both modes.
         if ( $is_default ) {
+            set_transient( $transient_key, '', DAY_IN_SECONDS );
             return;
         }
 
         if ( empty( $colors['base'] ) || empty( $colors['contrast'] ) ) {
+            set_transient( $transient_key, '', DAY_IN_SECONDS );
             return;
         }
 
@@ -280,6 +293,9 @@ if ( ! function_exists( 'wp_bootstrap_variation_colors' ) ) :
              . '[data-bs-theme=light]{' . $light_css . '}'
              . '[data-bs-theme=dark]{' . $dark_css . '}';
 
+        // Cache for 24 hours; invalidated on theme switch or global-styles save.
+        set_transient( $transient_key, $css, DAY_IN_SECONDS );
+
         // Attach after the compiled stylesheet so variation values override
         // Bootstrap's hardcoded dark-mode defaults via source order.
         wp_add_inline_style( 'wp-bootstrap-style', $css );
@@ -287,6 +303,16 @@ if ( ! function_exists( 'wp_bootstrap_variation_colors' ) ) :
 endif;
 add_action( 'wp_enqueue_scripts', 'wp_bootstrap_variation_colors', 30 );
 
+/**
+ * Invalidate the color variation CSS transient when global styles or theme change.
+ */
+add_action( 'switch_theme', function () {
+    delete_transient( 'wp_bootstrap_variation_css_' . md5( get_stylesheet() ) );
+} );
+add_action( 'save_post_wp_global_styles', function () {
+    delete_transient( 'wp_bootstrap_variation_css_' . md5( get_stylesheet() ) );
+} );
+
 /**
  * Build Bootstrap surface CSS variables for a given background/foreground pair.
  *

inc/Twig/TwigService.php

@@ -25,9 +25,9 @@ class TwigService
 
         $loader = new FilesystemLoader($viewsDir);
         $this->twig = new Environment($loader, [
-            'cache' => WP_DEBUG ? false : $cacheDir,
+            'cache'        => WP_DEBUG ? false : $cacheDir,
-            'debug' => WP_DEBUG,
+            'debug'        => WP_DEBUG,
-            'auto_reload' => true,
+            'auto_reload'  => WP_DEBUG,
         ]);
 
         $this->registerWordPressFunctions();

style.css

@@ -7,7 +7,7 @@ Description: A modern WordPress Block Theme built from scratch with Bootstrap 5.
 Requires at least: 6.7
 Tested up to: 6.7
 Requires PHP: 8.3
-Version: 1.0.8
+Version: 1.0.9
 License: GNU General Public License v2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html
 Text Domain: wp-bootstrap