test: add opt-in shifted FP32 Jet CV control

tests/validation/run_jet_circle_cv.py

@@ -18,11 +18,24 @@ CY = np.array([0, 0, 0, 1, -1, 1, -1, -1, 1])
 W = np.array([4 / 9] + [1 / 9] * 4 + [1 / 36] * 4)
 
 
-def case(scale=1, re=100, steps=800):
+def case(scale=1, re=100, steps=800, ddf_shifting=False):
     u = 0.03 / scale
     d = 24.084 * scale
     return dict(
         scale=scale,
+        ddf_shifting=bool(ddf_shifting),
+        storage_variant=dict(
+            name="shifted_fp32" if ddf_shifting else "unshifted_fp32",
+            device_populations="g=f-w" if ddf_shifting else "f",
+            device_dtype="float32",
+            equilibrium_path=(
+                "compute_feq_from_momentum" if ddf_shifting else "compute_feq"
+            ),
+            initial_physical_seed="historical FP32-rounded equilibrium, identical in both variants",
+            downloaded_populations="physical f, decoded by public stepper.download()",
+            downloaded_dtype="float64" if ddf_shifting else "float32",
+            raw_exchange="physical reaction and mass; no host weight correction",
+        ),
         re_d=re,
         beta=0.1,
         nx=192 * scale,
@@ -226,7 +239,7 @@ def run_case(c, ctx, output, provenance, continuation=False):
         collision="SRT",
         streaming="double_buffer",
         store_precision="FP32",
-        ddf_shifting=False,
+        ddf_shifting=c.get("ddf_shifting", False),
         les_enabled=False,
     )
     fine_cfg = LBMConfig(
@@ -237,7 +250,7 @@ def run_case(c, ctx, output, provenance, continuation=False):
         collision="SRT",
         streaming="double_buffer",
         store_precision="FP32",
-        ddf_shifting=False,
+        ddf_shifting=c.get("ddf_shifting", False),
         les_enabled=False,
     )
     obj = SimObject(
@@ -579,8 +592,15 @@ def main():
         action="store_true",
         help="Bounded ref0..800 scalar diagnostics at every root interval; sparse rays/fields",
     )
+    p.add_argument(
+        "--shifted-fp32",
+        action="store_true",
+        help="Opt-in shifted numerical-representation control for --dense-root; historical unshifted default unchanged",
+    )
     p.add_argument("--plan", action="store_true")
     a = p.parse_args()
+    if a.shifted_fp32 and not a.dense_root:
+        p.error("--shifted-fp32 requires the bounded --dense-root campaign")
     if a.steps <= 0 or a.steps > 3200:
         p.error("steps must be 1..3200")
     if a.re == 400 and not a.allow_re400:
@@ -593,7 +613,7 @@ def main():
     if a.continuation:
         if a.scale not in (1, 2) or a.re != 100 or a.steps != 3200:
             p.error("--continuation requires --re 100 --scale 1/2 --steps 3200")
-    c = case(a.scale, a.re, a.steps)
+    c = case(a.scale, a.re, a.steps, ddf_shifting=a.shifted_fp32)
     if a.continuation:
         from jet_cv_measurements import sample_steps, factors