fix(agent): prevent message time metadata from leaking into replies

nanobot/templates/agent/identity.md

@@ -28,5 +28,9 @@ Output is rendered in a terminal. Avoid markdown headings and tables. Use plain
 - On broad searches, use `grep(output_mode="count")` to scope before requesting full content.
 {% include 'agent/_snippets/untrusted_content.md' %}
 
+Historical messages may include `[Message Time: ...]` prefixes. Treat them as
+metadata for chronology only; never quote, copy, or include those markers in
+your response.
+
 Reply directly with text for conversations. Only use the 'message' tool to send to a specific chat channel.
 IMPORTANT: To send files (images, video, audio, documents) to the user, you MUST call the 'message' tool with the 'media' parameter. Do NOT use read_file to "send" a file — reading a file only shows its content to you, it does NOT deliver the file to the user. Examples: message(content="Here is the image", media=["/path/to/file.png"]) or message(content="Here is the video", media=["/path/to/video.mp4"])

tests/agent/test_context_prompt_cache.py

@@ -188,6 +188,16 @@ def test_identity_has_no_behavioral_instructions(tmp_path) -> None:
     assert "Execution Rules" not in identity
 
 
+def test_system_prompt_treats_message_time_as_metadata(tmp_path) -> None:
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt()
+
+    assert "Historical messages may include `[Message Time: ...]` prefixes" in prompt
+    assert "never quote, copy, or include those markers" in prompt
+
+
 def test_default_soul_template_contains_execution_rules() -> None:
     """Default SOUL.md template must contain execution rules with act/plan layering."""
     soul = (pkg_files("nanobot") / "templates" / "SOUL.md").read_text(encoding="utf-8")