fix: tolerate markdown-fenced JSON from LLM responses (v0.4.3)

Models like GPT 5.1 Nano ignore response_format: json_object and wrap
their JSON in ```json fences or add preamble text. New Json_Extractor
utility tries: (1) direct decode, (2) strip markdown fences, (3) find
outermost { ... } substring. Applied to analyzer and chief editor
parsers. Raw response logged on parse failure for debugging.

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

includes/core/class-json-extractor.php

@@ -0,0 +1,60 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Extracts valid JSON from potentially dirty LLM response strings.
+ *
+ * Many models ignore the `response_format: json_object` instruction and wrap
+ * their output in markdown fences, add preamble text, or append trailing
+ * commentary. This class strips all of that and returns clean decoded data.
+ *
+ * Triggered by: Any class that parses JSON from an LLM response.
+ * Dependencies: None (pure utility).
+ *
+ * @see core/class-content-analyzer.php — Uses this for analysis JSON parsing.
+ * @see core/class-chief-editor.php     — Uses this for editorial review JSON parsing.
+ */
+class PRAutoBlogger_Json_Extractor {
+
+	/**
+	 * Decode JSON from an LLM response, tolerating markdown fences and preamble.
+	 *
+	 * Attempts, in order:
+	 * 1. Direct json_decode (model returned clean JSON).
+	 * 2. Strip ```json ... ``` fences, then decode.
+	 * 3. Find the first `{` and last `}` and decode that substring.
+	 *
+	 * @param string $raw The raw LLM response content.
+	 * @return array<string, mixed>|null Decoded associative array, or null on failure.
+	 */
+	public static function decode( string $raw ): ?array {
+		$trimmed = trim( $raw );
+
+		// 1. Clean JSON — best case.
+		$decoded = json_decode( $trimmed, true );
+		if ( is_array( $decoded ) ) {
+			return $decoded;
+		}
+
+		// 2. Markdown-fenced JSON (```json ... ``` or ``` ... ```).
+		if ( preg_match( '/```(?:json)?\s*\n?(.*?)\n?\s*```/s', $trimmed, $matches ) ) {
+			$decoded = json_decode( trim( $matches[1] ), true );
+			if ( is_array( $decoded ) ) {
+				return $decoded;
+			}
+		}
+
+		// 3. Brute-force: find outermost { ... } substring.
+		$first_brace = strpos( $trimmed, '{' );
+		$last_brace  = strrpos( $trimmed, '}' );
+		if ( false !== $first_brace && false !== $last_brace && $last_brace > $first_brace ) {
+			$candidate = substr( $trimmed, $first_brace, $last_brace - $first_brace + 1 );
+			$decoded   = json_decode( $candidate, true );
+			if ( is_array( $decoded ) ) {
+				return $decoded;
+			}
+		}
+
+		return null;
+	}
+}