feat: update LLM prompts to return brief+content JSON

Replace _SUMMARY_USER, _CONCEPT_PAGE_USER, and _CONCEPT_UPDATE_USER to
request a JSON object with "brief" (one-line summary) and "content" (full
Markdown). Add TestParseBriefContent to tests/test_compiler.py.

Author: KylinMountain

openkb/agent/compiler.py

@@ -43,11 +43,14 @@
 Full text:
 {content}
 
-Write a summary page for this document in Markdown. Include:
-- Key concepts, findings, and ideas
-- [[wikilinks]] to concepts that could become cross-document concept pages
+Write a summary page for this document in Markdown.
 
-Return ONLY the Markdown content (no frontmatter, no code fences).
+Return a JSON object with two keys:
+- "brief": A single sentence (under 100 chars) describing the document's main contribution
+- "content": The full summary in Markdown. Include key concepts, findings, ideas, \
+and [[wikilinks]] to concepts that could become cross-document concept pages
+
+Return ONLY valid JSON, no fences.
 """
 
 
@@ -84,10 +87,13 @@
 This concept relates to the document "{doc_name}" summarized above.
 {update_instruction}
 
-Return ONLY the Markdown content (no frontmatter, no code fences). Include:
-- Clear explanation of the concept
-- Key details from the source document
-- [[wikilinks]] to related concepts and [[summaries/{doc_name}]]
+Return a JSON object with two keys:
+- "brief": A single sentence (under 100 chars) defining this concept
+- "content": The full concept page in Markdown. Include clear explanation, \
+key details from the source document, and [[wikilinks]] to related concepts \
+and [[summaries/{doc_name}]]
+
+Return ONLY valid JSON, no fences.
 """
 
 _CONCEPT_UPDATE_USER = """\
@@ -101,7 +107,11 @@
 information naturally — do not just append. Maintain existing \
 [[wikilinks]] and add new ones where appropriate.
 
-Return ONLY the Markdown content (no frontmatter, no code fences).
+Return a JSON object with two keys:
+- "brief": A single sentence (under 100 chars) defining this concept (may differ from before)
+- "content": The rewritten full concept page in Markdown
+
+Return ONLY valid JSON, no fences.
 """
 
 _LONG_DOC_SUMMARY_USER = """\

tests/test_compiler.py

@@ -61,6 +61,19 @@ def test_fenced_dict(self):
         assert parsed["create"] == []
 
 
+class TestParseBriefContent:
+    def test_dict_with_brief_and_content(self):
+        text = json.dumps({"brief": "A short desc", "content": "# Full page\n\nDetails."})
+        parsed = _parse_json(text)
+        assert parsed["brief"] == "A short desc"
+        assert "# Full page" in parsed["content"]
+
+    def test_plain_text_fallback(self):
+        """If LLM returns plain text, _parse_json raises — caller handles fallback."""
+        with pytest.raises((json.JSONDecodeError, ValueError)):
+            _parse_json("Just plain markdown text without JSON")
+
+
 class TestWriteSummary:
     def test_writes_with_frontmatter(self, tmp_path):
         wiki = tmp_path / "wiki"