test: expand security regression coverage

Agent-Logs-Url: https://github.com/MemPalace/mempalace/sessions/775f2fc4-3051-462e-8586-6d694b55da0d

Co-authored-by: igorls <4753812+igorls@users.noreply.github.com>

tests/test_query_sanitizer.py

@@ -102,6 +102,20 @@ class TestTailSentence:
         assert result["was_sanitized"] is True
         assert "MemPalace" in result["clean_query"] or "ChromaDB" in result["clean_query"]
 
+    def test_long_candidate_uses_last_sentence_fragment(self):
+        query = ("Prompt sentence. " * 30) + "Final search intent for architecture migration"
+        result = sanitize_query(query)
+        assert result["method"] == "tail_sentence"
+        assert result["clean_query"] == "Final search intent for architecture migration"
+
+    def test_long_candidate_strips_wrapping_quotes(self):
+        query = ("Prefix text " * 30) + '\n"' + ("x" * 260) + '"'
+        result = sanitize_query(query)
+        assert result["method"] == "tail_sentence"
+        assert not result["clean_query"].startswith('"')
+        assert not result["clean_query"].endswith('"')
+        assert len(result["clean_query"]) <= MAX_QUERY_LENGTH
+
 
 class TestTailTruncation:
     """Step 4: Fallback — take the last MAX_QUERY_LENGTH characters."""
@@ -119,6 +133,12 @@ class TestTailTruncation:
         result = sanitize_query(filler)
         assert "IMPORTANT_QUERY_CONTENT" in result["clean_query"]
 
+    def test_tail_sentence_fallback_preserves_tail_without_delimiters(self):
+        filler = ("x" * 260) + "IMPORTANT_QUERY_CONTENT"
+        result = sanitize_query(filler)
+        assert result["method"] == "tail_sentence"
+        assert "IMPORTANT_QUERY_CONTENT" in result["clean_query"]
+
 
 class TestLengthGuards:
     """Verify output length constraints."""