fix(agent): expose session timestamps in model context

Include persisted turn timestamps when assembling LLM prompts so relative-date references like yesterday and today have concrete anchors.

Made-with: Cursor

tests/agent/test_loop_save_turn.py

@@ -535,7 +535,10 @@ async def test_system_subagent_followup_is_persisted_before_prompt_assembly(tmp_
     )
 
     non_system = [m for m in seen["initial_messages"] if m.get("role") != "system"]
-    assert [m["content"] for m in non_system[:2]] == ["question", "working"]
+    assert "question" in non_system[0]["content"]
+    assert "working" in non_system[1]["content"]
+    assert "[Message Time:" in non_system[0]["content"]
+    assert "[Message Time:" in non_system[1]["content"]
     assert non_system[2]["content"].count("subagent result") == 1
     assert "Current Time:" in non_system[2]["content"]