feat(agent): prompt behavior directives, tool descriptions, and loop robustness

tests/agent/test_context_prompt_cache.py

@@ -148,6 +148,63 @@ def test_partial_dream_processing_shows_only_remainder(tmp_path) -> None:
     assert "recent question about K8s" in prompt
 
 
+def test_execution_rules_in_system_prompt(tmp_path) -> None:
+    """New execution rules should appear in the system prompt."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt()
+    assert "Act, don't narrate" in prompt
+    assert "Read before you write" in prompt
+    assert "verify the result" in prompt
+
+
+def test_channel_format_hint_telegram(tmp_path) -> None:
+    """Telegram channel should get messaging-app format hint."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt(channel="telegram")
+    assert "Format Hint" in prompt
+    assert "messaging app" in prompt
+
+
+def test_channel_format_hint_whatsapp(tmp_path) -> None:
+    """WhatsApp should get plain-text format hint."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt(channel="whatsapp")
+    assert "Format Hint" in prompt
+    assert "plain text only" in prompt
+
+
+def test_channel_format_hint_absent_for_unknown(tmp_path) -> None:
+    """Unknown or None channel should not inject a format hint."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    prompt = builder.build_system_prompt(channel=None)
+    assert "Format Hint" not in prompt
+
+    prompt2 = builder.build_system_prompt(channel="feishu")
+    assert "Format Hint" not in prompt2
+
+
+def test_build_messages_passes_channel_to_system_prompt(tmp_path) -> None:
+    """build_messages should pass channel through to build_system_prompt."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    messages = builder.build_messages(
+        history=[], current_message="hi",
+        channel="telegram", chat_id="123",
+    )
+    system = messages[0]["content"]
+    assert "Format Hint" in system
+    assert "messaging app" in system
+
+
 def test_subagent_result_does_not_create_consecutive_assistant_messages(tmp_path) -> None:
     workspace = _make_workspace(tmp_path)
     builder = ContextBuilder(workspace)