Enforce before/after diff requirement for all issues

server.js

@@ -99,14 +99,15 @@ Numbered list of concrete improvements, ranked ruthlessly by impact. No hand-wav
 Rules:
 - You MUST use exactly these five ## headings and no others.
 - ALWAYS reference line numbers from the provided source.
-- ALWAYS use \`\`\`diff blocks for code changes. EVERY item in Code Quality, Performance, Security, and Suggestions MUST have a diff. No exceptions.
-- DIFF FORMAT IS CRITICAL: Lines starting with \`-\` are OLD code being removed. Lines starting with \`+\` are NEW code being added. Lines with neither prefix are unchanged context. A changed line must appear TWICE: once with \`-\` (old), once with \`+\` (new). NEVER put \`+\` on a line and then \`-\` on the lines inside a block — that is nonsensical. Example of CORRECT diff:
+- EVERY ISSUE MUST HAVE A BEFORE/AFTER DIFF. No exceptions. No issue without a \`\`\`diff block. No diff without both \`-\` (before) and \`+\` (after) lines. If you cannot show a concrete fix, do not mention the issue.
+- DIFF FORMAT: Lines with \`-\` are BEFORE (old code). Lines with \`+\` are AFTER (new code). Lines with neither are context. Show what you're removing AND what you're replacing it with. Example:
 \`\`\`diff
   if err != nil {
 -     return result, err
 +     return Result{}, fmt.Errorf("wrapped: %w", err)
   }
 \`\`\`
+- NEVER output a diff with only \`-\` lines (that's deletion with no replacement) or only \`+\` lines (that's addition with no context). NEVER mix \`+\` and \`-\` illogically.
 - Do NOT pad the review with praise or pleasantries. Respect the reader's time.
 - If the code is genuinely excellent in some area, one dry sentence of acknowledgment is sufficient.
 - Be merciless but never wrong. Every criticism must be technically defensible.