fix(memory): ignore empty consolidation summaries

tests/agent/test_consolidator.py

@@ -873,7 +873,7 @@ class TestCompactIdleSession:
     async def test_nothing_summary_not_stored(
         self, real_consolidator, mock_provider, runtime
     ):
-        """LLM returns '(nothing)' → _last_summary NOT in metadata."""
+        """LLM returns '(nothing)' → neither history nor metadata stores it."""
         mock_provider.chat_with_retry.return_value = MagicMock(
             content="(nothing)", finish_reason="stop"
         )
@@ -891,6 +891,7 @@ class TestCompactIdleSession:
 
         reloaded = sessions.get_or_create("cli:nothing")
         assert "_last_summary" not in reloaded.metadata
+        assert real_consolidator.store.read_unprocessed_history(0) == []
 
     @pytest.mark.asyncio
     async def test_llm_failure_preserves_history_but_advances_replay_boundary(

tests/agent/test_context_prompt_cache.py

@@ -96,6 +96,17 @@ def test_unprocessed_history_injected_into_system_prompt(tmp_path) -> None:
     assert re.search(r"\[\d{4}-\d{2}-\d{2} \d{2}:\d{2}\]", prompt)
 
 
+def test_nothing_history_entry_is_not_injected(tmp_path) -> None:
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+    builder.memory.append_history("(nothing)")
+
+    prompt = builder.build_system_prompt()
+
+    assert "# Recent History" not in prompt
+    assert "(nothing)" not in prompt
+
+
 def test_recent_history_injection_is_session_scoped(tmp_path) -> None:
     workspace = _make_workspace(tmp_path)
     builder = ContextBuilder(workspace)