fix(image): prevent duplicate delivery and replay artifacts

tests/agent/test_context_prompt_cache.py

@@ -289,6 +289,18 @@ def test_build_messages_passes_channel_to_system_prompt(tmp_path) -> None:
     assert "messaging app" in system
 
 
+def test_system_prompt_keeps_message_tool_out_of_current_chat_replies(tmp_path) -> None:
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt(channel="slack")
+
+    assert "Do not use the 'message' tool for normal replies in the current chat" in prompt
+    assert "the runtime attaches those artifacts to the final assistant reply automatically" in prompt
+    assert "do not call 'message' just to announce or resend them" in prompt
+    assert "Wait for the tool results, then answer once" in prompt
+
+
 def test_subagent_result_does_not_create_consecutive_assistant_messages(tmp_path) -> None:
     workspace = _make_workspace(tmp_path)
     builder = ContextBuilder(workspace)

tests/agent/test_session_manager_history.py

@@ -245,14 +245,8 @@ def test_get_history_annotates_user_turns_but_not_assistant_turns():
     ]
 
 
-def test_get_history_annotates_proactive_assistant_deliveries_with_timestamps():
-    """Cron / heartbeat assistant pushes still carry a timestamp prefix.
-
-    These proactive deliveries can sit hours away from the next user reply,
-    so the model needs to know when they fired. They are rare enough that
-    they don't act as in-context demonstrations encouraging the model to
-    prefix its own normal replies with ``[Message Time: ...]``.
-    """
+def test_get_history_does_not_annotate_proactive_assistant_deliveries_with_timestamps():
+    """Assistant-side timestamp examples can leak back into future replies."""
     session = Session(key="test:proactive-timestamps")
     session.messages.append({
         "role": "assistant",
@@ -271,7 +265,7 @@ def test_get_history_annotates_proactive_assistant_deliveries_with_timestamps():
     assert history == [
         {
             "role": "assistant",
-            "content": "[Message Time: 2026-04-26T15:00:00]\n记得喝水",
+            "content": "记得喝水",
         },
         {
             "role": "user",
@@ -370,6 +364,41 @@ def test_get_history_ignores_media_kwarg_on_non_user_rows():
     assert history[0]["content"] == [{"type": "text", "text": "structured"}]
 
 
+def test_get_history_does_not_paste_assistant_media_paths_into_replay():
+    session = Session(key="test:assistant-media")
+    session.messages.append(
+        {
+            "role": "assistant",
+            "content": "来了 🎨",
+            "media": ["/home/user/.nanobot/media/generated/img_abc.png"],
+        }
+    )
+
+    history = session.get_history(max_messages=500)
+
+    assert history == [{"role": "assistant", "content": "来了 🎨"}]
+
+
+def test_get_history_sanitizes_existing_assistant_replay_artifacts():
+    session = Session(key="test:polluted-assistant")
+    session.messages.append(
+        {
+            "role": "assistant",
+            "content": (
+                "[Message Time: 2026-05-09 00:33:48]\n"
+                "来了 🎨\n"
+                "[image: /home/user/.nanobot/media/generated/img_old.png]\n\n"
+                "generate_image(\"16:9\")\n"
+                "message(\"来了 🎨\")"
+            ),
+        }
+    )
+
+    history = session.get_history(max_messages=500, include_timestamps=True)
+
+    assert history == [{"role": "assistant", "content": "来了 🎨"}]
+
+
 def test_get_history_respects_max_tokens(monkeypatch):
     session = Session(key="test:token-cap")
     session.messages.extend(