Support stationary bodies and geometry Jets on nested L2

README.md

@@ -158,30 +158,48 @@ Scope and limits:
       coarse_g, fine_g = run.download()  # coarse: NaN on every covered cell;
                                          # fine: NaN on every non-ACTIVE cell
   ```
-- Three levels (one nested chain, body-free): add `child=(x0, y0, x1, y1)` in
+- Three levels (one nested chain): add `child=(x0, y0, x1, y1)` in
   **L1 window cells** (the patch's fine grid including its 4-cell ghost band) and
   `child_block`, with `fine_block` and `base_block`. L2 must sit inside L1's
   ACTIVE cells, away from L1's ghost band and transfer footprint (checked before
   any GPU allocation). `initialize` and `download` take/return three arrays; each
   level is NaN on its non-ACTIVE (and child-covered) cells. One coarse step = 2 L1
-  steps = 4 L2 steps. One L1 patch only, no bodies/Jets.
+  steps = 4 L2 steps. One L1 patch only. Optional stationary circles and Jets
+  live on L2 via `child_objects` and `child_jets`; `fine_objects`/`jets` retain
+  their L1 meaning and must be empty in this mode. All object and Jet geometry
+  uses the **L0 edge frame**, not the child bounds' L1 window frame. L2 has
+  dx=dt=0.25, so prescribed lattice velocity is unchanged. Each whole body and
+  its BFL stencil must be inside L2 ACTIVE cells, outside the transfer footprint.
+  A Jet may select one physical body across multiple blocks, never two bodies.
 
   ```python
+  from CelerisLab.body.geometry.circle import CircleGeometry
+  from CelerisLab.body.objects import SimObject
+  from CelerisLab.body.jets import Jet, Tube, Parallel
+
   cfg = LBMConfig(nx=16, ny=16, viscosity=.1)
+  body = SimObject(0, geometry=CircleGeometry(8., 8., .8), center=(8., 8.), radius=.8)
+  jet = Jet(Tube((6.5, 8.), 0., 3., .3), Parallel(0.), amplitude=.002)
   rest = np.asarray(compute_feq_d2q9(1.0, 0.0, 0.0), np.float32)[:, None, None]
   with CudaContext(0) as ctx, FixedPatchStepper(
           cfg, (4, 4, 12, 12), context=ctx, fine_block=(4, 4), base_block=(4, 4),
-          child=(8, 8, 16, 16), child_block=(4, 4)) as run:
+          child=(8, 8, 16, 16), child_block=(4, 4),
+          child_objects=[body], child_jets=[jet]) as run:
       shapes = (run.patch.coarse_shape, run.patch.fine_shape, run.child_patch.fine_shape)
       run.initialize(*(np.broadcast_to(rest, (9, *s)) for s in shapes))  # 16², 24², 24²
-      run.step(32)
-      coarse_g, l1_g, l2_g = run.download()
+      run.step(4)
+      run.set_jet_amplitude(0, -.002, level=2)  # default level=1 still addresses L1
+      run.step(4)
+      coarse_g, l1_g, l2_g = run.download()  # solids/covered/nonleaves are NaN
   ```
 - Not available: per-link surface exchange/force readout in blocked mode,
-  checkpoints, moving bodies, bodies/Jets with three levels,
+  checkpoints, moving bodies, L1 bodies/Jets in a three-level chain,
   several patches per level with nesting, dynamic refinement, `Simulation`
   integration. Validation so far is storage/operator equivalence and short runs,
-  not accuracy, convergence or long-time stability.
+  not accuracy, convergence or long-time stability. The new L2-body GPU gates
+  (layouts, masks, amplitude reversal, legacy equivalence) and independent
+  every-substep numerical replay remain required acceptance checks; CPU tests
+  alone do not establish GPU numerical correctness.
 
 ## Installation