fix: rein in dbn-legal-agent feedback-loop contamination (stop seqs + JSON extract + system prompt)

includes/BvjAnalyzerAgent.php

@@ -842,8 +842,16 @@ Rules:
 - Respond in {$locale}.
 PROMPT;
 
+        $sysPrompt = $engine === 'dbn_legal'
+            // dbn-legal-agent has a fine-tune that appends self-rating feedback loops after the
+            // JSON. Explicitly forbid that pattern and stop before it can start.
+            ? 'You output valid JSON only. Output the JSON object, then stop immediately. '
+              . 'Do not add any self-assessment, rating, "END OF MESSAGE", feedback loop, '
+              . 'USER/SYSTEM turns, or any text after the closing brace of the JSON object.'
+            : 'You return valid JSON only. No markdown fences.';
+
         $messages = [
-            ['role' => 'system', 'content' => 'You return valid JSON only. No markdown fences.'],
+            ['role' => 'system', 'content' => $sysPrompt],
             ['role' => 'user',   'content' => $prompt],
         ];
         $opts = ['json' => true, 'temperature' => $temperature, 'max_tokens' => 3000, 'timeout' => 200];
@@ -865,9 +873,19 @@ PROMPT;
                     'temperature' => $temperature,
                     'max_tokens'  => 2800,
                     'timeout'     => 660,
+                    // Stop sequences cut generation the moment the feedback loop tries to start.
+                    'stop'        => ["\nEND OF MESSAGE", "\nPlease rate", "\nUSER:", "지금 번역하기"],
                 ], $emit ? static function () use ($emit): void {
                     $emit('progress', ['detail' => 'dbn-legal-agent generating…']);
                 } : null);
+
+                // Belt-and-suspenders: even with stop sequences the model may still include
+                // preamble or trailing junk. Extract only the first complete {...} object.
+                $jsonStart = strpos($raw, '{');
+                $jsonEnd   = strrpos($raw, '}');
+                if ($jsonStart !== false && $jsonEnd !== false && $jsonEnd > $jsonStart) {
+                    $raw = substr($raw, $jsonStart, $jsonEnd - $jsonStart + 1);
+                }
             } elseif ($engine === 'gpu') {
                 $response = dbnToolsCallGpuLlm($messages, $opts);
                 $raw = (string)($response['choices'][0]['message']['content'] ?? '');
@@ -915,6 +933,9 @@ PROMPT;
             'max_tokens'  => $options['max_tokens'] ?? 2800,
             'stream'      => true,
         ];
+        if (!empty($options['stop']) && is_array($options['stop'])) {
+            $payload['stop'] = $options['stop'];
+        }
         $body    = json_encode($payload, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
         $headers = [
             'Content-Type: application/json',