test(observability): add compose-invariant test scaffold

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_observability.py

@@ -0,0 +1,25 @@
+"""Compose-level invariants for the observability port.
+
+refs docs/superpowers/specs/2026-05-01-observability-port-design.md
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import yaml
+
+ROOT = Path(__file__).resolve().parents[1]
+COMPOSE = ROOT / "compose.yml"
+
+
+def _load() -> dict:
+    return yaml.safe_load(COMPOSE.read_text())
+
+
+def _services() -> dict:
+    return _load().get("services", {})
+
+
+def test_compose_has_services():
+    assert _services(), "compose.yml has no services"