test: add optional public macro CV observations

tests/validation/run_jet_circle_cv.py

@@ -74,7 +74,25 @@ def cv(g, fluid, origin, rectangle, nu, h=0.5):
     Cauchy stress from centred velocity gradients, NOT postcollision non-equilibrium.
     Rectangle faces lie on cell edges; fluid mask excludes the staircase cylinder.
     """
-    rho, mom, vel = moments(g)
+    return _cv_quantities(*moments(g), fluid, origin, rectangle, nu, h)
+
+
+def cv_from_macros(rho, ux, uy, fluid, origin, rectangle, nu, h=0.5):
+    """Same CV calculation from public macros, in one common length/time frame.
+
+    ``origin`` is the lower cell edge, ``h`` the cell width, and ``nu`` uses
+    that frame. Returns [mass, Px, Py] inventory and outward total flux.
+    Crop fields/mask together and translate origin before calling if desired.
+    No boundary-exchange observation enters this independent estimator.
+    """
+    rho = np.asarray(rho, np.float64)
+    if rho.ndim != 2 or any(np.shape(v) != rho.shape for v in (ux, uy, fluid)):
+        raise ValueError("CV macros and fluid mask must have matching 2D shapes")
+    vel = np.asarray([ux, uy], np.float64)
+    return _cv_quantities(rho, rho[None] * vel, vel, fluid, origin, rectangle, nu, h)
+
+
+def _cv_quantities(rho, mom, vel, fluid, origin, rectangle, nu, h):
     x0, y0, x1, y1 = np.rint((np.array(rectangle) - np.tile(origin, 2)) / h).astype(int)
     np.testing.assert_allclose(
         np.array([x0, y0, x1, y1]) * h + np.tile(origin, 2), rectangle, atol=1e-12