feat(host): add _emit_step helper for lifecycle logging

l4d2host/instances.py

@@ -8,6 +8,14 @@ from l4d2host.service_control import start_service, stop_service
 from l4d2host.spec import load_spec
 
 
+def _emit_step(msg: str, on_stdout: Callable[[str], None] | None, passthrough: bool) -> None:
+    formatted = f"Step: {msg}"
+    if on_stdout is not None:
+        on_stdout(formatted)
+    elif passthrough:
+        print(formatted, flush=True)
+
+
 DEFAULT_ROOT = DEFAULT_LEFT4ME_ROOT
 
 

l4d2host/tests/test_initialize.py

@@ -1,6 +1,8 @@
+import sys
+from io import StringIO
 from pathlib import Path
 
-from l4d2host.instances import initialize_instance
+from l4d2host.instances import initialize_instance, _emit_step
 
 
 def test_initialize_writes_files(tmp_path: Path) -> None:
@@ -31,3 +33,21 @@ def test_initialize_uses_configured_left4me_root(tmp_path: Path, monkeypatch) ->
 
     env = (tmp_path / "instances/alpha/instance.env").read_text()
     assert f"L4D2_LOWERDIRS={tmp_path}/overlays/standard:{tmp_path}/installation" in env
+
+
+def test_emit_step_uses_callback() -> None:
+    calls: list[str] = []
+    _emit_step("test step", on_stdout=calls.append, passthrough=False)
+    assert calls == ["Step: test step"]
+
+
+def test_emit_step_uses_passthrough_stdout(monkeypatch) -> None:
+    fake_out = StringIO()
+    monkeypatch.setattr(sys, "stdout", fake_out)
+    _emit_step("passthrough step", on_stdout=None, passthrough=True)
+    assert fake_out.getvalue() == "Step: passthrough step\n"
+
+
+def test_emit_step_does_nothing_if_no_target() -> None:
+    _emit_step("silent step", on_stdout=None, passthrough=False)
+