feat(lib): implement A-4 M0~M1 BaseAgentAdapter pattern and resolve_home contract

.agents/skills/lib.sh

@@ -1120,7 +1120,8 @@ PYEOF
 if [ -f "$SKILL_DIR/lib_py/verify_session.py" ]; then
   VERIFY_SESSION_PYTHON="$(cat "$SKILL_DIR/lib_py/verify_session.py")"
 else
-  VERIFY_SESSION_PYTHON=""
+  echo "ERROR: lib_py/verify_session.py missing" >&2
+  return 1 2>/dev/null || exit 1
 fi
 
 verify_session_uuid() {