CoreBoost v3.3.6

🐛 Fixed - LCP Foreground Injection (cb-lcp) Not Firing

Root Cause

inject_lcp_foreground_image() used a subcapture group for attribute extraction:
([^>]*\bclass=["\'][^"\']*\bcb-lcp\b[^"\']*["\'][^>]*). PCRE backtracking on the trailing
[^>]* could cause attributes such as data-coreboost-deferred-youtube or the inline style
to fall outside $matches[2], resulting in the function finding no image URL and silently
returning the original tag — so cb-lcp-img never appeared in the source.

A second cascading failure: even when smart_youtube_blocking was ON, the image URL was not being
found because Elementor applies the fallback as an inline CSS background on the wrapper element
(not in data-settings) and that path was never checked.

A third latent bug: start_output_buffer() only ran the output buffer when smart_youtube_blocking
or a script/CSS defer feature was active. If only enable_lcp_foreground_injection was on,
the buffer never started and injection never ran.

Changes

• inject_lcp_foreground_image() fully rewritten. Outer regex simplified to
  /<[a-z][a-z0-9]*\s[^>]*\bcb-lcp\b[^>]*>/i — no subcapture groups. All four attribute
  extractions run directly on $matches[0] (the full opening tag string), eliminating the
  PCRE backtracking failure mode entirely.
• 3-level image URL cascade:
  1. data-settings JSON → background_video_fallback.url then background_image.url
     (present when smart_youtube_blocking is OFF).
  2. data-coreboost-deferred-youtube JSON → fallback.url / fallback (string)
     (present when smart_youtube_blocking has stripped data-settings).
  3. Inline style attribute — per Elementor's architecture, the video fallback is
     rendered as style="background: url('...') 50% 50%; background-size: cover;" on the
     wrapper element by the Group_Control_Background CSS selector. This level is always
     present in the rendered HTML and was previously never read.
• <link rel="preload"> now injected directly from inject_lcp_foreground_image(). After
  the preg_replace_callback pass, the first resolved image URL is injected as a
  <link rel="preload" fetchpriority="high"> before </head>. This makes the head preload
  independent of Hero_Optimizer::preload_video_hero() and the preload_method setting —
  so it fires correctly regardless of which hero detection method is configured.
• start_output_buffer() gate extended to include
  !empty($this->options['enable_lcp_foreground_injection']). Previously the output buffer
  only ran when a script/CSS defer or smart_youtube_blocking feature was also active; disabling
  those features would silently prevent LCP injection from running at all.

Files Modified

• includes/public/class-resource-remover.php — inject_lcp_foreground_image() full rewrite; start_output_buffer() buffer-start condition

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