research: Dütsch config from the shipped config_lbm.json schema; real-loader test

The generated config failed the real loader (KeyError: cuda). It now copies
src/CelerisLab/configs/config_lbm.json and overrides only grid, physics,
collision/streaming/storage, y walls, LES off and uniform inlet profile;
inlet scheme and outlet mode stay the template's and are recorded in
case.json. New CPU test loads the generated file with load_lbm_config.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

research/duetsch_re100_kc5/run.py

@@ -20,13 +20,26 @@ import numpy as np
 import protocol as p
 
 
+TEMPLATE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "..", "src",
+                        "CelerisLab", "configs", "config_lbm.json")
+
+
 def config(D, box, T):
+    """Shipped config_lbm.json (full parser schema) with only the case fields
+    overridden: grid, still fluid (velocity 0), nu from Re, MRT, uniform inlet
+    profile, bounce-back y walls. Inlet scheme and outlet mode stay the
+    template's (zou_he_local, neq_extrap) and are recorded in case.json."""
     u = p.KC * D / T
     n = int(round(box * D))
-    return {"grid": {"lattice_model": "D2Q9", "nx": n, "ny": n, "nz": 1},
-            "physics": {"data_type": "FP32", "viscosity": u * D / p.RE, "velocity": 0.0, "rho": 1.0},
-            "method": {"collision": "MRT", "streaming": "double_buffer", "store_precision": "FP32",
-                       "ddf_shifting": False, "y_wall_bc": "bounce_back"}}, u, n
+    with open(TEMPLATE) as fh:
+        cfg = json.load(fh)
+    cfg["grid"].update(lattice_model="D2Q9", nx=n, ny=n, nz=1)
+    cfg["physics"].update(data_type="FP32", viscosity=u * D / p.RE, velocity=0.0, rho=1.0)
+    cfg["method"].update(collision="MRT", streaming="double_buffer", store_precision="FP32",
+                         ddf_shifting=False, y_wall_bc="bounce_back")
+    cfg["method"]["les"]["enabled"] = False
+    cfg["method"]["inlet"]["profile"] = "uniform"
+    return cfg, u, n
 
 
 def main():
@@ -85,6 +98,7 @@ def main():
             json.dump(dict(D=D, T=T, box=args.box, n=n, u_max=u_max, nu=cfg["physics"]["viscosity"],
                            tau=3 * cfg["physics"]["viscosity"] + 0.5, A=A, steps=steps,
                            cycles=args.cycles, F_ref=0.5 * u_max ** 2 * D,
+                           inlet=cfg["method"]["inlet"], outlet=cfg["method"]["outlet"],
                            weights=[r[8] for r in samples]), fh)
     finally:
         sim.close()

tests/unit/test_duetsch_protocol.py

@@ -85,3 +85,22 @@ def test_exact_point_inside_body_is_missing_even_with_fluid_corners():
     assert value is None and used == () and total == 0.0
     value, used, total = p.sample(field, fluid, 3.35, 3.0, centre, radius)  # just outside
     assert value is not None and total > 0.0
+
+
+def test_generated_config_passes_the_real_loader(tmp_path):
+    import json
+    import sys
+    sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "research/duetsch_re100_kc5"))
+    try:
+        import run
+    finally:
+        sys.path.pop(0)
+    from CelerisLab.config import load_lbm_config
+    cfg_dict, u_max, n = run.config(20, 10.0, 2520)
+    path = tmp_path / "config_lbm.json"
+    path.write_text(json.dumps(cfg_dict))
+    cfg = load_lbm_config(str(path))
+    assert (cfg.nx, cfg.ny) == (n, n) == (200, 200)
+    assert cfg.collision == "MRT" and cfg.streaming == "double_buffer" and not cfg.ddf_shifting
+    assert cfg.velocity == 0.0 and cfg.viscosity == pytest.approx(u_max * 20 / 100)
+    assert cfg.y_wall_bc == "bounce_back"