# Supported settings: 2D Jet + fixed multilevel refinement (candidate c95a7ba)

Every entry names the guard that enforces it (file:line at c95a7ba) and, where one
exists, an existing test that exercises it. A setting not listed here is not
claimed. Observations at the end are tied to the exact case in which they were
measured; they are not general bounds.

## Lattice, storage, collision

| Setting | Supported | Guard |
|---|---|---|
| Dimension / lattice | 2D D2Q9 only (3D refinement is future work) | `lbm/refinement.py:65`, `lbm/kernels/blocks.cu:25`, `lbm/kernels/refinement.cu:26` |
| Precision / streaming | FP32 storage, double buffer | same guards |
| Collision on refinement levels | SRT or MRT; TRT and LES rejected | `lbm/refinement.py:65`, `lbm/refinement.py:457` |
| Shifted (ddf_shifting) storage | only when every level is blocked; dense or mixed rejected | `lbm/refinement_stepper.py:198`, `:469`; `lbm/kernels/refinement.cu:26` (dense patch kernel unshifted only) |
| Fine relaxation | 1/tau_fine must lie inside the configured omega guards | `lbm/refinement.py:80` |
| Uniform blocked backend `PeriodicBlockStepper` | doubly periodic, SRT only, stationary passive circles | `lbm/block_stepper.py:84`, `:91`, `:45`-`:67` |

Tests: `tests/unit/test_refinement_mrt.py`, `tests/validation/multigrid/test_refinement_mrt_gpu.py`,
`tests/unit/test_shifted_storage.py`, `tests/unit/test_shifted_block_operators.py`.

## Refinement hierarchy (`FixedPatchStepper(cfg, *, context, refinements, ...)`)

| Setting | Supported | Guard |
|---|---|---|
| Depth | at least one refinement level; one entry per level in `level_blocks`/`level_objects`/`level_jets` | `lbm/refinement_stepper.py:72`, `:75` |
| Single L1 rectangle | two-coarse-cell margin to the domain edge | `lbm/refinement.py:73` |
| Several L1 rectangles (union) | require `level_blocks[0]` and `level_blocks[1]`; transfers must close (dependency checks, no fixed gap rule) | `lbm/refinement_stepper.py:84`; `lbm/refinement.py:283`-`:295` |
| Nested levels | depth >= 3 must be all blocked; a blocked level requires blocked levels below; a scalar child needs a scalar parent | `lbm/refinement_stepper.py:82`, `:87`; `lbm/hierarchy.py:54` |
| Nested transfer support | child only over inherited ACTIVE cells, donors/receivers uncovered ACTIVE, no child over the parent restriction footprint | `lbm/refinement.py:391`-`:407` |
| Tile shape | `(by, bx)`; the level allocation must be divisible by the tile (no partial tiles yet) | `lbm/refinement_stepper.py:78`; `lbm/refinement.py:246` |
| Coarse boundary | `periodic`, `slot_reservoir` or `channel` | `lbm/refinement_stepper.py:177` |
| `slot_reservoir` | on-site velocity bottom slot, reservoir top, velocity 0, 2 <= slot width < nx, patch rows 4..ny-4 | `lbm/refinement_stepper.py:205`, `:212`; `lbm/refinement.py:546` |
| `channel` | all levels blocked; Zou-He inlet, pressure-NEQ outlet, stationary bounce-back walls; transfers away from the closure | `lbm/channel.py:22`, `:26`, `:43`, `:54` |
| Explosion | `constant` (default); `projected_linear` only periodic, all-blocked SRT, no bodies/Jets, no LES (experimental) | `lbm/refinement_stepper.py:188`, `:193` |
| L2 runtime remap (`remap_child`) | periodic three-level L2 sets only, no L0/L1 bodies, identical pinned boundary | `lbm/refinement_stepper.py:557`, `:567`-`:581` |

Tests: `tests/unit/test_refinement_three_level_multipatch.py`, `tests/validation/multigrid/test_refinement_multipatch.py`,
`test_refinement_three_level.py`, `test_refinement_three_level_multipatch_gpu.py`, `test_refinement_blocked_base.py`,
`test_refinement_blocked_fine.py`, `test_channel_root_gpu.py`, `tests/unit/test_channel_root.py`,
`tests/unit/test_projected_pair_stepper.py`, `test_runtime_child_remap_gpu.py`, `test_pinned_body_remap_gpu.py`.

## Bodies and Jets on refined levels

| Setting | Supported | Guard |
|---|---|---|
| Bodies | stationary circles without sensor/force-region roles, entirely inside the patch union, fully resolved, disjoint, stencil away from the two-hop transfer footprint | `lbm/refinement.py:474`-`:542` |
| Level | not on L0; only on the finest level of a nested hierarchy | `lbm/refinement_stepper.py:80`, `:89` |
| Jet condition | velocity only; `pressure` is reserved and raises NotImplementedError | `body/jets.py:148`, `:150` |
| Jet geometry | each Jet selects resolved links of exactly one stationary body; no Jet/Jet or Jet/SurfaceActuation overlap; abs(amplitude) < 1 lattice | `body/jets.py:155`, `:175`, `:177`, `:255`, `:261`, `:263` |
| Jets with shifted storage | only in the all-blocked stepper with SRT and no LES | `body/jets.py:249` |
| SurfaceActuation | unshifted storage only | `body/objects.py:155` |
| Raw boundary exchange (force) | blocked body levels only; the window ledger requires `observe_raw_exchange` | `lbm/refinement_stepper.py:264`, `:269` |
| Checkpoint with Jets | refused | `simulation.py:687` |

Raw exchange is the cut-link momentum reaction (wall + aperture), not a validated
nozzle thrust or stress load. Jet amplitude is a lattice velocity, not a flow rate.

Tests: `tests/unit/test_jets.py`, `test_jets_review.py`, `test_shifted_jets.py`, `test_raw_exchange.py`,
`tests/validation/multigrid/test_refinement_jets.py`, `test_shifted_jets_gpu.py`, `test_raw_exchange_gpu.py`,
`test_exchange_window.py`, `test_fine_surface_gpu.py`.

## Observations from specific tested cases (not general bounds)

- SRT channel root vs uniform OneStep, strict-parity case
  (`tests/validation/multigrid/test_channel_root_gpu.py`): 1 of 4320 compared values differs,
  max abs 2.33e-10, max rel 1.77e-7 (about 2 ULP). The test remains failed; its cause and any
  general bound are unresolved. The corresponding MRT comparison is bitwise equal.
- Periodic Taylor-Green Re 100, current checkout 36ffc8b1 (V3 matched pair, N128 depth 2):
  every per-sample screen passed; the constant explosion's aggregate worst velocity L2,
  0.004418, exceeds its preregistered 0.002 budget, while projected_linear passed that budget.
- Curved-wall pressure (pilot harness, exact-q analytic annulus, tau 0.8): the coarse swirl r1
  case exceeded its terminal density-gain cap (1.105e-4 vs 1e-4), so the frozen 9-case matrix
  is NOT_ESTABLISHED. No validated fix exists. This is a pilot harness, not production code.
- DFG 2D-1 Re 20 (V4, SRT, t* 60, pressure-NEQ outlet and local Zou-He inlet): refined and uniform
  runs were NOT_STEADY under the frozen steady rule, so no interval verdict was given.

## Not supported in this release

3D, dynamic/automatic AMR (tagging, time-varying hierarchies beyond `remap_child`),
moving bodies on refined levels, pressure Jets, Jet checkpoints, LES or TRT on refined
levels, partial (non-dividing) tiles.