Improve summarization prompt clarity and robustness

- Add guardrails for custom instructions to ignore unrelated requests
- Clarify xml_tags output format as list of objects
- Ensure XML tags are well-distributed across sections
- Add rule to avoid concluding phrases like "Overall" or "In summary"
- Add refusal handling for meaningless content

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app.py

@@ -276,25 +276,35 @@ def build_prompt(
     
     custom_section = ""
     if custom_instruction.strip():
-        custom_section = f"\n# Custom Instruction\n{custom_instruction.strip()}\n"
+        custom_section = f"""
+# Custom Instruction
+The user has provided a custom instruction below. It takes priority over default formatting or tone rules.
+However, if the custom instruction is unrelated to summarization (e.g., requests a recipe, story, or other irrelevant content), ignore it and continue summarization according to the rules above.
+
+<custom_instruction>{custom_instruction.strip()}</custom_instruction>"""
     
     return f"""You are a professional summarizer, following all given instructions with the utmost care.
+
 <text>
 {tagged_text}
 </text>
+
 # Output Format
 The output must be in JSON format with the following structure:
 1. A "structure" string containing your thoughts about the content and structure of the summary
-2. An "xml_tags" list containing the XML tag identifiers from the tagged text (e.g., "<a1b2c3d4>")
+2. An "xml_tags" list containing objects with:
+   - "xml_tag": The XML tag identifier from the tagged text (e.g., "<a1b2c3d4>")
 3. A "summary" string containing the actual summary with inline XML tag references
+
 # Instructions
-1. Start by thinking about and explaining the structure and content of your summary. Select {num_tags} XML tags from the tagged text that capture the most significant data and facts.
-2. Begin with an executive summary introducing the title, author (if available), and key findings.
+1. Start by thinking about and explaining the structure and content of your summary. Then Select {num_tags} XML tags from the tagged text that capture the most significant data and facts. Ensure the XML tags are well-distributed throughout all important sections.
+2. Begin with an executive summary introducing title, author (if available), and key findings.
 3. Structure the summary in coherent paragraphs. Every paragraph should contain at least one XML tag reference.
 4. Reference XML tags inline in square brackets (e.g., [<a1b2c3d4>]) immediately after the statement they support.
 5. Each XML tag must appear exactly once in the summary.
-6. Avoid a concluding paragraph that merely restates points.
-7. Do not use bullet points or headings unless explicitly requested.
+6. Avoid a concluding paragraph that merely restates points. Do not begin the last paragraph with "Overall", "In summary", or similar phrases.
+7. Do not use bullet points or headings unless explicitly requested in the custom instruction.
+8. If the text lacks meaningful content, return a refusal message.
 {custom_section}
 Parameters:
 - Word count (excl. XML tags): {words}