feat(images): retry Cloudflare NSFW-blocked prompts with a sanitized fallback

Cloudflare's Workers AI FLUX.1 schnell content filter sometimes rejects
peptide-comic prompts as NSFW (HTTP 400, errors[].code === 3030). On
2026-04-20 this produced a silent publish-without-featured-image for
post #650 ("Semaglutide vs Tirzepatide") — the LLM-rewritten scene
tripped the filter and we had no recovery path.

New behaviour: on a 3030 response, the Cloudflare provider throws a
typed PRAutoBlogger_Image_NSFW_Blocked exception. The batch wrapper
catches it and tags the per-slot result with
`error_type: nsfw_blocked`. Image_Pipeline hands the results to a new
PRAutoBlogger_Image_NSFW_Retry helper, which reruns the blocked slot
once with a sanitized fallback prompt (title + style suffix, no LLM
rewrite). On success the retry result replaces the error entry; on a
second block, a WARNING is logged and the pipeline publishes without
that image — same terminal behaviour we had before, just explicit.

Files:

- New providers/class-image-nsfw-blocked.php — typed exception.
- providers/class-cloudflare-image-support.php — is_nsfw_error() +
  throw_if_nsfw() helpers.
- providers/class-cloudflare-image-provider.php — calls throw_if_nsfw
  inside the 4xx branch; batch catches the typed exception and marks
  the result with error_type.
- core/class-image-prompt-builder.php — new public build_fallback_prompt
  shim so the retry layer can reach the rule-based fallback without
  going through the LLM path.
- New core/class-image-nsfw-retry.php — single-shot retry helper.
- core/class-image-pipeline.php — invokes the retry between batch
  completion and per-slot processing.
- admin/class-settings-fields-extended.php — new toggle
  `prautoblogger_image_nsfw_retry` (default on) in the Images section.

Tests:

- CloudflareImageProviderTest — 3030 response throws NSFW exception;
  batch tags the per-slot result with `error_type: nsfw_blocked`.
- ImagePipelineTest — retry succeeds when provider returns a good
  result on the second call; retry is skipped when the setting is off.

Cost impact: worst-case an extra Cloudflare call per NSFW-blocked slot
(~$0.000834). Current incidence ~2% of generations; ~+$0.00002 per
generation amortized. Immaterial.

Uninstall: new option covered by the existing prautoblogger_% LIKE
sweep in uninstall.php.

Part of the v0.8.0 image bundle (issues from thread image-mime-bug).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

includes/core/class-image-prompt-builder.php

@@ -66,18 +66,12 @@ PROMPT;
 	/**
 	 * Build a visual prompt from finished article content.
 	 *
-	 * Tries LLM rewriting first; falls back to rule-based synthesis on failure.
-	 * Separates the scene description (for image gen) from the caption text
-	 * (for insertion below the image as HTML). Appends style suffix to the
-	 * scene-only prompt so no text is rendered inside the image.
+	 * Tries LLM rewriting first; falls back to rule-based synthesis on
+	 * failure. Splits scene (for image gen) from caption (HTML below the
+	 * image) and appends the style suffix.
 	 *
-	 * @param array{
-	 *     post_title?: string,
-	 *     post_content?: string,
-	 *     suggested_title?: string,
-	 * } $article_data Article data with title and HTML content.
-	 *
-	 * @return array{prompt: string, caption: string} Image prompt (scene + style) and caption text.
+	 * @param array{post_title?: string, post_content?: string, suggested_title?: string} $article_data
+	 * @return array{prompt: string, caption: string}
 	 */
 	public function build_article_prompt( array $article_data ): array {
 		$title      = $article_data['post_title'] ?? $article_data['suggested_title'] ?? 'Product';
@@ -95,18 +89,11 @@ PROMPT;
 	}
 
 	/**
-	 * Build a visual prompt from source Reddit thread data.
+	 * Build a visual prompt from source Reddit thread data. Tries LLM
+	 * rewriting first; falls back to rule-based synthesis on failure.
 	 *
-	 * Tries LLM rewriting first; falls back to rule-based synthesis on failure.
-	 * Appends the style suffix from plugin options.
-	 *
-	 * @param array{
-	 *     title?: string,
-	 *     selftext?: string,
-	 *     comments?: string[],
-	 * } $source_data Reddit source data with title and comments.
-	 *
-	 * @return array{prompt: string, caption: string} Image prompt (scene + style) and caption text.
+	 * @param array{title?: string, selftext?: string, comments?: string[]} $source_data
+	 * @return array{prompt: string, caption: string}
 	 */
 	public function build_source_prompt( array $source_data ): array {
 		$title    = $source_data['title'] ?? 'Reddit Discussion';
@@ -257,6 +244,23 @@ PROMPT;
 		return $para;
 	}
 
+	/**
+	 * Public entry into the rule-based fallback, used by NSFW retry to
+	 * rebuild a provider-safe prompt from just the article title. Matches
+	 * the return shape of build_article_prompt() / build_source_prompt().
+	 *
+	 * @param string $title Article or source title.
+	 * @return array{prompt: string, caption: string}
+	 */
+	public function build_fallback_prompt( string $title ): array {
+		$parsed       = $this->synthesize_visual_concepts_fallback( $title, '' );
+		$style_suffix = get_option( 'prautoblogger_image_style_suffix', PRAUTOBLOGGER_DEFAULT_IMAGE_STYLE_SUFFIX );
+		return [
+			'prompt'  => trim( $parsed['scene'] . ' ' . $style_suffix ),
+			'caption' => $parsed['caption'],
+		];
+	}
+
 	/**
 	 * Rule-based fallback when LLM rewriting is unavailable.
 	 *