fix: keep ACP stdout protocol-clean

Route AIAgent print output to stderr via _print_fn for ACP stdio sessions.
Gate quiet-mode spinner startup on _should_start_quiet_spinner() so JSON-RPC
on stdout isn't corrupted. Child agents inherit the redirect.

Co-authored-by: Git-on-my-level <Git-on-my-level@users.noreply.github.com>

tests/acp/test_session.py

@@ -1,5 +1,7 @@
 """Tests for acp_adapter.session — SessionManager and SessionState."""
 
+import contextlib
+import io
 import json
 from types import SimpleNamespace
 import pytest
@@ -329,3 +331,40 @@ class TestPersistence:
         assert restored is not None
         assert restored.agent.provider == "anthropic"
         assert restored.agent.base_url == "https://anthropic.example/v1"
+
+    def test_acp_agents_route_human_output_to_stderr(self, tmp_path, monkeypatch):
+        """ACP agents must keep stdout clean for JSON-RPC stdio transport."""
+
+        def fake_resolve_runtime_provider(requested=None, **kwargs):
+            return {
+                "provider": "openrouter",
+                "api_mode": "chat_completions",
+                "base_url": "https://openrouter.example/v1",
+                "api_key": "test-key",
+                "command": None,
+                "args": [],
+            }
+
+        def fake_agent(**kwargs):
+            return SimpleNamespace(model=kwargs.get("model"), _print_fn=None)
+
+        monkeypatch.setattr("hermes_cli.config.load_config", lambda: {
+            "model": {"provider": "openrouter", "default": "test-model"}
+        })
+        monkeypatch.setattr(
+            "hermes_cli.runtime_provider.resolve_runtime_provider",
+            fake_resolve_runtime_provider,
+        )
+        db = SessionDB(tmp_path / "state.db")
+
+        with patch("run_agent.AIAgent", side_effect=fake_agent):
+            manager = SessionManager(db=db)
+            state = manager.create_session(cwd="/work")
+
+        stdout_buf = io.StringIO()
+        stderr_buf = io.StringIO()
+        with contextlib.redirect_stdout(stdout_buf), contextlib.redirect_stderr(stderr_buf):
+            state.agent._print_fn("ACP noise")
+
+        assert stdout_buf.getvalue() == ""
+        assert stderr_buf.getvalue() == "ACP noise\n"

tests/test_run_agent.py

@@ -2612,6 +2612,24 @@ def test_aiagent_uses_copilot_acp_client():
     assert mock_acp_client.call_args.kwargs["args"] == ["--acp", "--stdio"]
 
 
+def test_quiet_spinner_allowed_with_explicit_print_fn(agent):
+    agent._print_fn = lambda *_a, **_kw: None
+    with patch.object(run_agent.sys.stdout, "isatty", return_value=False):
+        assert agent._should_start_quiet_spinner() is True
+
+
+def test_quiet_spinner_allowed_on_real_tty(agent):
+    agent._print_fn = None
+    with patch.object(run_agent.sys.stdout, "isatty", return_value=True):
+        assert agent._should_start_quiet_spinner() is True
+
+
+def test_quiet_spinner_suppressed_on_non_tty_without_print_fn(agent):
+    agent._print_fn = None
+    with patch.object(run_agent.sys.stdout, "isatty", return_value=False):
+        assert agent._should_start_quiet_spinner() is False
+
+
 def test_is_openai_client_closed_honors_custom_client_flag():
     assert AIAgent._is_openai_client_closed(SimpleNamespace(is_closed=True)) is True
     assert AIAgent._is_openai_client_closed(SimpleNamespace(is_closed=False)) is False

tests/tools/test_delegate.py

@@ -34,7 +34,7 @@ def _make_mock_parent(depth=0):
     """Create a mock parent agent with the fields delegate_task expects."""
     parent = MagicMock()
     parent.base_url = "https://openrouter.ai/api/v1"
-    parent.api_key = "parent-key"
+    parent.api_key="***"
     parent.provider = "openrouter"
     parent.api_mode = "chat_completions"
     parent.model = "anthropic/claude-sonnet-4"
@@ -47,6 +47,9 @@ def _make_mock_parent(depth=0):
     parent._delegate_depth = depth
     parent._active_children = []
     parent._active_children_lock = threading.Lock()
+    parent._print_fn = None
+    parent.tool_progress_callback = None
+    parent.thinking_callback = None
     return parent
 
 
@@ -228,7 +231,7 @@ class TestDelegateTask(unittest.TestCase):
     def test_child_inherits_runtime_credentials(self):
         parent = _make_mock_parent(depth=0)
         parent.base_url = "https://chatgpt.com/backend-api/codex"
-        parent.api_key = "codex-token"
+        parent.api_key="***"
         parent.provider = "openai-codex"
         parent.api_mode = "codex_responses"
 
@@ -249,6 +252,49 @@ class TestDelegateTask(unittest.TestCase):
             self.assertEqual(kwargs["provider"], parent.provider)
             self.assertEqual(kwargs["api_mode"], parent.api_mode)
 
+    def test_child_inherits_parent_print_fn(self):
+        parent = _make_mock_parent(depth=0)
+        sink = MagicMock()
+        parent._print_fn = sink
+
+        with patch("run_agent.AIAgent") as MockAgent:
+            mock_child = MagicMock()
+            MockAgent.return_value = mock_child
+
+            _build_child_agent(
+                task_index=0,
+                goal="Keep stdout clean",
+                context=None,
+                toolsets=None,
+                model=None,
+                max_iterations=10,
+                parent_agent=parent,
+            )
+
+        self.assertIs(mock_child._print_fn, sink)
+
+    def test_child_uses_thinking_callback_when_progress_callback_available(self):
+        parent = _make_mock_parent(depth=0)
+        parent.tool_progress_callback = MagicMock()
+
+        with patch("run_agent.AIAgent") as MockAgent:
+            mock_child = MagicMock()
+            MockAgent.return_value = mock_child
+
+            _build_child_agent(
+                task_index=0,
+                goal="Avoid raw child spinners",
+                context=None,
+                toolsets=None,
+                model=None,
+                max_iterations=10,
+                parent_agent=parent,
+            )
+
+        self.assertTrue(callable(mock_child.thinking_callback))
+        mock_child.thinking_callback("deliberating...")
+        parent.tool_progress_callback.assert_not_called()
+
 
 class TestToolNamePreservation(unittest.TestCase):
     """Verify _last_resolved_tool_names is restored after subagent runs."""