research: VIV driver reads diagnostics by MovingTables.DIAG name; coupling-contract README

Index values are unchanged (1, 3, 7, 10, 13); the run recorded at fb507aa1
used the same columns. Research-only.

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

docs/development/src_coherence.md

@@ -3,9 +3,12 @@
 Owner direction 2026-10-28: unified style over historical compatibility, inside `src`.
 No numerical change is intended. Stages after 5f69eba: 65339ab (one boundary/Jet record,
 host preparation helpers, pair accessors), c5a3cdb (`block_collide` families), 442979b
-(exchange metadata on the boundary record). Each was checked by parent/candidate
-config.h/PTX comparison and host/GPU equality runs; c5a3cdb changed the PTX of the two
-channel-root SRT modules only (omega load/clamp moved, outputs exact).
+(exchange metadata on the boundary record). All three received parent/candidate
+generated-config and host/GPU equality checks. Only the collision slice ran a new PTX
+matrix (a4fc46d, whose src is identical to c5a3cdb); 65339ab and 442979b reused prior
+PTX evidence after unchanged CUDA/compiler and generated-input checks. In the collision
+matrix, only the two channel-root SRT modules changed PTX (omega load/clamp moved);
+their parent/candidate outputs matched exactly in the exercised cases.
 
 ## Conventions (defined once, in `lbm.hierarchy.Hierarchy`)
 

docs/lifecycle.md

@@ -6,8 +6,8 @@ it is; it adds no framework. Line references are to candidate 0f8fdbc3.
 | Class | Contents | How it changes | Owner rule |
 |---|---|---|---|
 | 1. Module and its globals | Compile-time (visible to the compiler, fixed per module): `config.h` macros incl. `NX`/`NY`, `COLLISION_MODEL`, `BLOCK_ROOT_BC`, `WALL_*`. Runtime per-module globals (not visible to the compiler; written by host code): `__constant__` `d_params`, `d_w`, `d_cx`, `d_cy`, `d_block_channel`, `d_block_wall`; plus bound kernel handles | Globals are written once by the owner right after `load_module`. Uniform grid: `Simulation._recompile` (construction, body-topology sync) loads a new module and re-uploads; `update_runtime_params` rewrites `d_params` (omega, force, n_objects) between runs. Steppers: never rewritten after construction, so they are immutable for the instance's lifetime although they are runtime values. The blocked slot/reservoir root reads its slot from the `d_block_wall` constant (the former dense route used `WALL_*` macros; both were bit-identical in the parity gates). | Every owner loads its own module (`compiler.load_module` = `module_from_file`, no cache). A loaded module is never shared between live owners: globals are per module, so sharing would share mutable `d_params`. |
-| 2. Geometry, layout, tables | flags, curved-link tables, block layouts and halo pairs, transfer (explode/coalesce) tables, block kinds | Immutable for the life of an instance. Uniform grid: rebuilt by body sync. `FixedPatchStepper`: a geometry change is a new instance (`remap_finest`), committed only after a successful transfer. | No in-place table edits. |
-| 3. Controls and dependent boundary columns | Jet amplitude -> per-link `surface_velocity`; body actions (uniform grid) | Between steps, without a table or module rebuild (`set_jet_amplitude`). | Input (index, level, amplitude) is validated before any device write; invalid input changes nothing and the instance stays usable. The host copy commits only after the upload returned. Any error after validation leaves the device column undefined and fails the instance: `FixedPatchStepper` status `failed`, `Simulation._failed`; every later device-touching public method (`Simulation`: `stream`, `set_jet_amplitude`, `initialize`, `sync_bodies`, `run`/`step`, `read_surface_exchange`, `read_body(s)`, `get_macroscopic`, `get_ddf`, `update_runtime_params`, `snapshot`, `restore`, save/load checkpoint) raises; cached host readers and host-side staging (e.g. `get_flags`, `add_body`/`remove_body` before a sync) do not touch the device and stay callable. `close()` still releases resources and stays retryable. |
+| 2. Geometry, layout, tables | flags, curved-link tables, block layouts and halo pairs, transfer (explode/coalesce) tables, block kinds | Immutable for the life of an instance, except translating circles on the uniform grid: their swept-band flags and cut links are rewritten on the device every advancing step (`MovingCircleCells`/`MovingCircleLinks`, docs/moving_bodies.md); the host flag mirror is then stale for those cells. Uniform grid otherwise: rebuilt by body sync. `FixedPatchStepper`: a geometry change is a new instance (`remap_finest`), committed only after a successful transfer. | No in-place table edits. |
+| 3. Controls and dependent boundary columns | Jet amplitude -> per-link `surface_velocity`; body actions (uniform grid) | Between steps, without a table or module rebuild (`set_jet_amplitude`). | Input (index, level, amplitude) is validated before any device write; invalid input changes nothing and the instance stays usable. The host copy commits only after the upload returned. Any error after validation leaves the device column undefined and fails the instance: `FixedPatchStepper` status `failed`, `Simulation._failed`; every later device-touching public method (`Simulation`: `stream`, `set_jet_amplitude`, `initialize`, `sync_bodies`, `run`/`step`, `read_surface_exchange`, `read_body(s)`, `get_macroscopic`, `get_ddf`, `update_runtime_params`, `snapshot`, `restore`, save/load checkpoint) raises; cached host readers and host-side staging (e.g. `get_flags` without translating circles, `add_body`/`remove_body` before a sync) do not touch the device and stay callable; with translating circles `get_flags` reads the device flags back and refuses after a failure. Translating-circle targets follow the same rule: `set_body` validates before mutation, the applied offset commits only after a successful synchronized step, and a failed moving step fails the instance (docs/moving_bodies.md). `close()` still releases resources and stays retryable. |
 | 4. Per-step state | population double buffers and their parity, raw-exchange ledgers, observations | Device-only during `step(n)` / `run(n)`; buffer swaps are host-handle swaps. | Valid on the host only after the single wait at the end of the call. |
 
 Storage routes are separate concerns:

docs/moving_bodies.md

@@ -0,0 +1,447 @@
+# Moving circles on the uniform dense grid
+
+## Status and user guide (current)
+
+Development-stage feature, integrated from the reviewed slices S1–S3a
+(production code identical to `653fd997`). Physical evidence and its limits:
+`docs/validation/moving_bodies_stage1.md`. The force used as a structural RHS
+is a declared stage choice, not an established result.
+
+*What it does.* Translating circles (with optional spin) on the dense
+double-buffer D2Q9 path: per-step cut links from an FP64 geometry record
+(M2 `MovingCircleLinks`), reclassification and refill of covered/uncovered
+cells (M1 `MovingCircleCells`), moving-wall Bouzidi with wall velocity
+`u + omega x r`, and separate per-body diagnostics.
+
+*API.*
+- `Simulation.add_body("circle", center=(x, y), radius=r,
+  translation=Translation(offset_box, max_speed))` before `initialize()`;
+  `offset_box = (x_min, x_max, y_min, y_max)` in lattice cells around the
+  base centre (must contain 0), `0 < max_speed ≤ .5`.
+- `set_body(id, offset=(dx, dy), vx=..., vy=..., omega=...)` sets a pending
+  target (validated against the applied offset: box, Euclidean step ≤ .5
+  cell, speed, no sliding hold); `vx`/`vy` are the interval wall velocity.
+- `run(1)` advances a pending target and commits it only after the step
+  synchronizes with `no_donor == 0`; `run(n > 1)` with a pending target
+  raises; without a target `run(n)` holds the geometry (spin allowed).
+  Direct `LBMStepper.step` refuses while a target is pending.
+- `moving_diagnostics()` returns per body the columns of
+  `MovingTables.DIAG` (CME, Wen term, link mass, cover/uncover momentum and
+  mass, eq_only, no_donor, crossings) accumulated since obs were zeroed;
+  `obs`/`read_force` keep their contract (CME on the body).
+- `get_flags()` reads device flags back when moving circles exist.
+
+*Supported:* dense double buffer, D2Q9, FP32 unshifted, SRT/MRT, circles,
+spin. *Rejected before mutation:* EsoPull, ddf shifting, D3Q19, refinement /
+blocked steppers, Jets or surface actuation on a moving circle,
+`sync_bodies` and checkpoints while a moving circle exists, swept bands that
+touch the domain edge, other bodies, sensors or force regions.
+
+*Failure lifecycle.* Device-side failures (upload, step, sync, no_donor)
+mark the Simulation failed; later run/step/sync/checkpoint calls and direct
+stepper calls refuse until `close()`.
+
+*Known limitations.* No mass correction at curved walls (static or moving);
+cover/uncover and Wen terms are diagnostics, not a selected force law; the
+host loop costs a fixed per-step synchronization (≈ 1 ms/step measured on a
+7.2 M-cell grid, run(1) class); outer boundaries are the single dense
+channel package (see `configs/CONFIG.md`).
+
+## Design record (staged contract, kept as written)
+
+The sections below are the contract the slices were reviewed against
+(S0 → S3a). They are kept unchanged for provenance; where they say "draft",
+"proposed" or "until S2/S3", the status above supersedes them.
+
+Original scope (Frank via TRON, thread C0C78UFKGRM/1793335557.460509):
+uniform-grid prescribed translation and single-cylinder free transverse VIV;
+base main `b2034f87e03656c5f67ab88562a70d6c338b9918`.
+
+## 1. Working standards
+
+- Lean, readable kernels in the existing idiom (`kernels/step/*.cu`, shared
+  `apply_bouzidi_link`); Python manages state and validation. No framework,
+  no compatibility layer, no new dependency.
+- The existing stationary/rotating path (`CurvedBoundaryKernel`, host link
+  packing, `sync_bodies`) stays byte-identical. Moving circles are a separate,
+  explicitly enabled path with its own numerical contract (this file).
+- One authority per state (section 4). No per-step full-domain download,
+  rebuild or recompile; local swept-band device updates are in scope.
+- Small slices (S1 host spec, S2 kernels without motion, S3 motion + refill,
+  S4 oscillator); each reviewed SHA is frozen before targeted runs.
+- Tolerances, benchmark parameters and the force composition used in the
+  structural RHS are declared before the runs that judge them. Fresh vs carried
+  evidence and existing baseline failures are recorded; smoke, convergence and
+  physical validation are reported separately. No undeclared force filtering.
+- External code (waLBerla GPLv3, FluidX3D source-available, VIVSIM) is a
+  concept reference only; nothing is copied.
+
+## 2. Current update order (main b2034f87, dense double buffer)
+
+`Simulation.run(n)`: upload host action (if `upload_act`) → zero obs (if
+`zero_obs`) → `DoubleBufferStepper.step(n)` → download obs → synchronize.
+
+Per step (`lbm/stepper.py` `step`):
+
+1. `CurvedBoundaryKernel` over the packed cut links: reads post-collision
+   `G^{n-1}` at `k_f` (and `k_f - c` for q < 1/2), adds the moving-wall term
+   (`Uw = -omega*ry, Vw = omega*rx` + optional per-link `surface_velocity`),
+   writes the reflected value into slot `opp` of the solid node `k_s`, and
+   accumulates `c(f_toward + f_reflected)` and torque into `obs`.
+2. `OneStep` pull/collide `ddf → temp` (collides FLUID cells; obstacle
+   interiors flagged `SOLID|OBSTACLE|BC_CURVED`), then buffer swap.
+3. `ForceRegionKernel`, `SensorKernel`.
+
+Raw `obs` force is the force **on the body** (link derivation in section 6;
+DFG docs report `Cd > 0` from it). Translation `vx, vy` in the action slots is
+currently stored but not read by any curved kernel.
+
+## 3. Proposed update order (moving circles)
+
+Per step n, before the existing step 1:
+
+- **M1 `MovingCircleCells`** (one thread per swept-band cell): classify with the
+  analytic predicates `in_old = inside(x, c^{n-1})`, `in_new = inside(x, c^n)`;
+  write `flag = in_new ? SOLID|OBSTACLE|BC_CURVED : FLUID`; covered cells
+  (`!in_old && in_new`) accumulate `node_cover`; fresh cells
+  (`in_old && !in_new`) are refilled (section 5) and accumulate `node_uncover`.
+- **M2 `MovingCircleLinks`** (one thread per band cell × direction): compute
+  q and hit point at `c^n` (FP64, same formula as `find_circle_intersection`,
+  same clamp [0.01, 1] and fallback classes as `CircleGeometry.build_cut_links`),
+  skip non-cut slots, call `apply_bouzidi_link` with
+  `u_w = (vx^n, vy^n) + omega × (hit - c^n)`, accumulate the link terms
+  (section 6).
+
+Then the unchanged steps 1–3. M2 must follow M1 because a q < 1/2 link may
+read `k_f - c` at a fresh cell.
+
+Exclusivity: moving bodies are never packed into the `CurvedBoundaryKernel`
+link arrays (`n_curved` covers stationary/rotating bodies only), so M2 is the
+sole writer of their solid slots and the sole source of their link force; no
+double write and no double `obs`. The stationary path's packing, launch and
+arithmetic are unchanged.
+
+Completeness: after M1, every (fluid cell, direction) pair in the swept band
+whose neighbour is `in_new` is visited by M2. This holds because the band is
+the circle AABB at the declared extreme offsets plus 2 cells, and the host
+rejects per-step moves with `|c_new - c_old|_2 > 0.5` and bands touching the domain edge,
+other bodies, sensors or force regions. Each M2 write lands at
+`index_f(k_s, opp)`, the exact slot the adjacent fluid cell pulls, so every
+fluid pull from a solid slot of a moving body is BFL-written.
+
+## 4. State, masks and authority
+
+- Host `ObjectState` is the single authority for one displacement
+  `offset = (dx, dy)` relative to the immutable base centre, plus
+  `velocity = (vx, vy)` and `omega`. Centres are always derived
+  (`c = base + offset`), never stored as independent state. Velocity is
+  supplied, never differenced from offsets.
+- `c^{n-1}` is derived from the last *committed* offset, `c^n` from the
+  offset being applied. Per body a small device **motion record**
+  `{c^{n-1}, c^n, u^n}` is uploaded with the action buffer; action-slot meaning
+  is not overloaded. (CANDIDATE layout; OPEN.)
+- Fail-closed commit: an enqueued upload is not a completed one. The new
+  offset becomes the committed offset only after the stream synchronization
+  that follows the upload and the step group succeeds. Any upload or later
+  synchronization failure leaves host and device motion state unknown: the
+  simulation is marked unusable (existing `_require_usable` lifecycle), and
+  no API may report a host/device match afterwards.
+
+### 4a. Applied geometry vs pending target (CANDIDATE, narrow API)
+
+Two distinct facts per moving body, one authority each:
+`applied` = offset of the geometry last applied on the device, changed only
+by a successful commit; `pending` = an optional requested target
+`(offset, velocity)`, changed only by `set_body`. A setter returning proves
+nothing about the device. The uploaded motion record is derived each run:
+`{c_old = base + applied, c_new = base + (pending.offset if pending is not
+None else applied), u = pending.velocity if pending is not None else 0}`
+(explicit `is not None`, so a zero offset or zero velocity is a valid target). Translational wall velocity exists only on a step
+that advances to a pending target; a hold step (`c_old == c_new`) has
+translational `u_w = 0` (spin unchanged), so a non-advancing circle never
+acts as a sliding wall. One moving step consumes one target.
+
+| situation | contract |
+|---|---|
+| `set_body` target | validated against `applied` (box, `|Δc|_2 ≤ 0.5` cell, speed bound) before mutation; on success replaces `pending` |
+| target with `offset == applied` and nonzero translational velocity | `ValueError` before mutation (would be a hold step with sliding wall velocity) |
+| two setters before a run | last wins; each validated against `applied`, not against the earlier pending target |
+| `run(1)` with pending | upload record, step, sync; on success `applied := pending.offset` (applied stores only the offset), `pending := None` |
+| `run(1)` without pending | hold: `c_old == c_new`, no cover/uncover, links at `applied`, translational `u_w = 0` |
+| `run(n > 1)` with pending | `ValueError` before mutation (single-step-only moving API) |
+| `run(n > 1)`, no pending | allowed: hold for n steps, translational `u_w = 0`, spin only |
+| `run(0)` | no motion upload, no commit; `pending` kept |
+| validation failure | `ValueError`, nothing mutated, retry allowed |
+| upload/launch/sync failure after enqueue | simulation unusable; `applied` and `pending` are not reported as device truth; no re-entry |
+
+Displacement norm: Euclidean per-step `|c_new - c_old|_2 ≤ 0.5` lattice
+cells (declared bound; CANDIDATE value).
+- Membership is never read from a flag that M1 is overwriting. The host
+  verifies at `add_body` that every swept-band cell has base flag FLUID, so the
+  band's base state is known without reading `flag_gpu`.
+- `flag_gpu` is the device authority for band cells while a moving body
+  exists; the host flag mirror is stale for those cells and is not used.
+
+## 5. Refill of fresh cells (CANDIDATE)
+
+- Stored time level: everything in `ddf` at M1 is post-collision `G^{n-1}`; the
+  refill writes all 9 slots at that same level, so every slot of a fresh cell
+  that the following pull or a q < 1/2 link may read is defined. Donor values
+  are read at the same level `G^{n-1}` (old-fluid cells, untouched by M1).
+- `G = f_eq(rho_bar, u_w(x)) + G_neq(x_d)` where `rho_bar` = mean density of
+  valid neighbours and `x_d` = the valid neighbour best aligned with the outward
+  normal `(x - c^n)/|x - c^n|`; `G_neq(x_d) = G(x_d) - f_eq(rho(x_d), u(x_d))`.
+- Valid donor: inside the domain, base FLUID, `!in_old && !in_new`.
+- Sets: `V(x)` = the 8 lattice neighbours that are in the domain, base FLUID
+  and `!in_old && !in_new`. `rho_bar` = mean density over `V(x)`. NEQ donor =
+  the member of `V(x)` with the largest `c·n` among those with `c·n > 0`
+  (`n` = outward normal at `c^n`); none → NEQ part 0 (counted as `eq_only`).
+- `V(x)` empty → no defined density: the cell is refilled with
+  `f_eq(RHO, u_w(x))` so all 9 slots stay defined, the `no_donor` counter is
+  incremented, and the host treats `no_donor > 0` after the run as a hard
+  failure (simulation unusable). It is not a silent fallback.
+- Non-emptiness is NOT assumed from the displacement bound. Geometry
+  assumptions: circle radius `R ≥ R_min` (CANDIDATE 4 cells), `|Δc|_2 ≤ 0.5`.
+  S1 includes a host enumeration over sub-cell centre positions and
+  displacement directions on a fine grid within these bounds that checks every
+  fresh cell has nonempty `V(x)`; it is evidence for those bounds, not a
+  proof, and runtime keeps the counter.
+- Fresh cells only write, old-fluid cells only read: no race.
+
+## 6. Discrete momentum ledger (to review; not a selection)
+
+Notation per step n: `F^n` = fluid set after M1; links L = (k_f, dir) at
+`c^n`; `f_t = G_dir(k_f)`; `f_r` = value M2 writes into `(k_s, opp)`.
+Fluid momentum before streaming:
+
+    P_pre = P(G^{n-1} on F^{n-1}) - sum_cover sum_q c_q G_q + sum_fresh sum_q c_q G_q^refill
+
+During the pull, every population entering a fluid cell comes from a fluid
+cell except the BFL-written slots; `f_t` leaves into solid and is never pulled
+by a fluid cell. Collision conserves momentum for SRT/MRT without forcing.
+Hence, in exact arithmetic,
+
+    P_fluid^n - P_fluid^{n-1} = - sum_L c (f_t + f_r) - I_cover + I_uncover + B^n + S^n
+
+with `B^n` external-boundary momentum (inlet/outlet/walls) and `S^n` forcing.
+So **`F_CME + node_cover - node_uncover`** is, by construction, the body
+momentum that balances the fluid ledger of *this* storage/update order.
+Branch details: halfway fallback links (`f_r = f_t` plus the moving-wall
+addend) and q < 1/2 links enter the link accumulators exactly like Bouzidi
+links, with `c(f_t + f_r)`. In the q < 1/2 branch `G_dir(k_f - c)` is an
+interpolation input only, not a fluid-momentum sink. Pull-slot completeness
+is the section 3 contract. The scope excludes `ddf_shifting` (rejected), so
+the unshifted force form applies. The balance is a fluid-side identity; it
+does not close body+fluid globally in a domain with inlet/outlet/forcing
+(`B^n`, `S^n`), and the solid-slot writes are boundary plumbing, not physical
+streaming packets.
+
+The Wen 2014 relative-velocity link sum adds `-u_w (f_t - f_r) = u_w dm` per
+link (`dm = f_r - f_t`, the BFL mass defect). That term has no counterpart in
+the fluid ledger above. Peng et al. (PRE 2016 submitted, §II.C, Eqs. 20–21)
+show for a straight wall that the bounce-back error accumulated before a node
+switch cancels with the switching momentum. Whether `sum u_w dm` approximates
+`I_cover - I_uncover` here (implying double counting if both are used) is
+**NOT demonstrated** for this implementation: it needs a bounded experiment
+(prescribed slow translation; cumulative `sum u_w dm` vs cumulative node
+impulse, per crossing cycle). Momentum conservation is also distinct from
+Galilean invariance, which G4 tests.
+
+External reference note: waLBerla's covered/refill momentum switches
+(`conserveMomentumWhenMapping`, `conserveMomentumWhenRestoring`) default to
+false (Astra), so their existence does not establish which combination its
+validation cases use. A bookkeeping identity alone does not select the
+physical force either.
+
+Mass ledger (same proposition status). With `M^n` the active-fluid mass
+summed over `F^n` at the sample point,
+
+    M^n - M^{n-1} = sum_L dm - m_cover + m_uncover + B_m^n
+
+(`dm = f_r - f_t`, `m_cover`/`m_uncover` = summed `sum_q G` of covered and
+refilled cells, `B_m` external-boundary mass flux; collision conserves mass).
+
+Sample point (fixed): post-collision storage after the swap of step n, i.e.
+the same level `G` that M1 reads at step n+1; both ledgers are evaluated
+there. Ledger residual = left side minus every listed term. Zero mass flux
+does not imply zero momentum exchange: closed walls (bounce-back, free-slip)
+still exchange momentum, so "no inlet/outlet, no forcing" does NOT give
+`B = S = 0`. The rounding-level momentum check therefore uses either a
+momentum-isolated case (periodic in both directions, no forcing) or counts
+the wall impulse explicitly as part of `B`; the mass check may use a closed
+domain. Otherwise `B`, `S` are not separately measured, the residual is
+reported as their estimate and is not a pass criterion.
+Both ledger identities are **proposed, unreviewed**: they are not called
+proven until review and a host replay agree.
+
+Accumulators (separate, per body, per step window; all reported raw):
+`link_cme`, `link_wen_correction` (= `sum u_w dm`), `node_cover`,
+`node_uncover` (momentum), `link_dm`, `mass_cover`, `mass_uncover` (mass),
+plus counters of crossings, `eq_only` and `no_donor`, so force spikes can be
+correlated with crossing events.
+
+**OPEN — structural RHS candidates (not selected):**
+(a) `link_cme + node_cover - node_uncover`; (b) `link_cme + link_wen_correction`
+(no node impulse). Selection follows the ledger review and the bounded
+experiment above.
+
+## 7. Rejection semantics
+
+- Before any mutation (`ValueError`, no device write, host state unchanged):
+  moving body with EsoPull, `ddf_shifting`, refinement/blocked stepper, D3Q19,
+  Jets or surface actuation on that body, `sync_bodies`/checkpoint while a
+  moving body exists; swept band touching domain boundaries, other bodies,
+  sensors or force regions; `set_body` offset outside the declared box,
+  per-step move `|c_new - c_old|_2 > 0.5` cell (the single bound of 4a), speed
+above the declared bound.
+- Host motion state is committed only after the upload *and* the following
+  synchronization of the step group succeed (section 4); any failure in
+  between makes the simulation unusable and no host/device match is reported.
+- The only soft device diagnostic is `eq_only` (NEQ part omitted, counted).
+  `no_donor > 0` is a hard failure: it is checked after the step group and
+  before the step is committed or any results are returned; on failure the
+  simulation is unusable (section 5).
+
+## 8. Coupling and units (CANDIDATE)
+
+Lattice units, rho0 = 1, per unit span. Step n uses `c^n`, `u^n` and yields
+`F^n`. Weak staggered update
+`v^{n+1} = v^n + (F^n - c v^n - k y^n)/m`, `y^{n+1} = y^n + v^{n+1}`
+(Newmark is an alternative; OPEN). Mass, natural frequency, damping and `U_r`
+follow the chosen benchmark's own definitions. Leontini, Thompson & Hourigan,
+JFS 22:857–864 (2006), DOI 10.1016/j.jfluidstructs.2006.04.003, as read by
+Grok from the full text: Re = 200, `m* = m/m_f = 10` (m_f displaced fluid
+mass), `zeta = c/c_crit = 0.01`, `U* = U/(f_N D)` with `f_N` the natural
+frequency in fluid assuming an inviscid added-mass term; the paper also
+reports frequencies normalised by the in-vacuo value. Our runner derives `k`
+from that in-fluid `f_N` (added-mass coefficient as stated in the paper) and
+never from the vacuum formula; `c_crit` convention and the original
+comparison data are still OPEN. Stability/convergence is gated by fluid
+time/space refinement of the coupled run, not assumed from the mass ratio;
+structural sub-stepping does not substitute for fluid-coupling time
+refinement.
+
+## 9. Gates (map; tolerances OPEN, declared before runs)
+
+G0 zero-motion regression, split: G0a populations of the existing stationary
+and spin-only path bitwise unchanged vs main; G0b moving path at rest (with
+and without spin) reproduces the stationary link set and populations; force
+estimator outputs are compared separately from populations, since the moving
+path adds estimator terms · G1 raw force sign (`Cd > 0`) ·
+G2/G3 prescribed translation incl. ledger accumulators · G4 matched
+relative-flow (moving body in quiescent fluid vs fixed body in uniform
+stream), optional boost, co-moving sanity · G5 Dütsch et al. 1998 Re 100,
+KC 5 in-line (needs 2-component offset) · G6 Leontini free transverse VIV
+(m* = 10, ζ = 0.01, Re = 200, definitions pending) · G7 time-level contract
+frozen before the oscillator.
+
+Candidate pre-run engineering tolerances (Astra; for discussion, not
+literature limits or measured outcomes; norms, averaging window, convergence
+protocol and physical reference uncertainty must be fixed before adoption, and
+none may be weakened after seeing runs):
+normalised momentum-ledger residual FP32 ≤ 5e-6 (FP64 oracle ≤ 2e-13);
+10-cycle relative mass drift ≤ 1e-4; prescribed-motion grid study D = 40/80/160
+with change in the force-response amplitude (observed quantity and norm to be
+named before adoption) ≤ 2 % and phase ≤ 2°; enlarged domain
+amplitude change ≤ 1 %; matched-frame force RMS ≤ 2 % and improving with
+refinement; VIV refinement amplitude ≤ 2 %, frequency ≤ 1 %, five consecutive
+cycle amplitudes within 1 %.
+
+Conditions stated before any moving kernel (S2/S3), not only at the
+oscillator stage: (i) fluid refinement protocol for the prescribed-motion
+gates — diffusive scaling (dx halved, dt quartered, physical Re, KC and
+amplitude fixed), the observed quantities and norms named in advance;
+(ii) Galilean constant-boost G4-boost requires boundaries compatible with a
+uniform boost (periodic in the boost direction or boundaries that move with
+it); if the current dense configuration cannot represent that, G4-boost is
+recorded as not runnable rather than replaced by another test.
+
+## 10. Proposed minimal S1 scope (host only; held until cross-review)
+
+- `add_body` moving-circle declaration: base centre, declared offset box
+  (x/y), speed bound; swept-band computation and band-placement validation.
+- `set_body(offset=..., velocity=..., omega=...)` validation before mutation
+  (section 7), applied/pending state and the run-transition table of 4a,
+  and the fail-closed commit of section 4.
+- Host enumeration check of refill-donor non-emptiness (section 5) within
+  the declared `R_min` and displacement bound.
+- Motion-record host layout and upload path; exclusion of moving bodies from
+  the packed `CurvedBoundaryKernel` links (stationary packing unchanged).
+- Explicit rejections for unsupported modes.
+- S1 execution guard: until the S2 moving kernels exist, any `run(n)` with
+  `n > 0` (and `step(n)`) while a moving body is declared raises before any
+  device mutation (no action/motion upload, no launch), including the
+  nominal at-rest case, because the moving body is excluded from the static
+  packed links and nothing else would apply its boundary. `run(0)` keeps its
+  existing behaviour. Simulations without moving bodies are unaffected.
+  Preparation/commit helpers are exercised by host tests with mocks; no
+  operational unsupported stepping path is exposed.
+- Host tests (Astra runs them): rejection-before-mutation, band geometry,
+  derived centres, fail-closed behaviour under an injected upload/sync
+  failure, stationary packing byte-identical, execution guard (positive-step
+  run with a moving body raises before upload/launch; stationary unaffected). No kernels, no GPU runs, no
+  y-only VIV oscillator (S4), no force RHS.
+
+## 10a. S2a — fixed-centre moving links (implemented on `claude/moving-bodies-s2a`)
+
+- `MovingCircleLinks` (`kernels/step/moving_circle.cu`, dense double buffer)
+  runs before the static curved kernel when moving tables are attached: one
+  thread per (band cell, direction) slot, FP64 `{cx, cy, r}` at the applied
+  offset, q/hit/clamp/fallback in the order of `build_cut_links` with explicit
+  `_rn` operations (host/device bit parity is a test target, not a claim),
+  then the unchanged `apply_bouzidi_link` with spin wall velocity only.
+- `obs` keeps its contract (CME and torque from `apply_bouzidi_link`). A
+  separate per-body diagnostics buffer receives `cme`, the Wen term
+  `u_w * dm`, `link_dm` and the link count from the same link outputs; it is
+  zeroed with obs and only exists when moving circles do. Optional
+  `slot_debug` (q, fallback, rx, ry per slot) is null in production.
+- Displacement is disabled: `set_body(offset=..., vx=..., vy=...)` on a
+  translating circle raises before mutation, before and after initialize, so
+  no pending target can exist and `run`/`step`/direct `LBMStepper.step` all
+  hold at the applied geometry. `initialize()` never reads or consumes
+  `pending`. `stepper.blocked` is cleared only when the moving tables are
+  attached (initialize, stepper recreation).
+- S3 rule (not implemented): once targets are re-enabled, any pending target
+  must raise in `run`/`step` and in `LBMStepper.step` alike before any launch,
+  swap or step-count change; zero-step calls never consume it.
+- Not validation: a pass of the zero-motion gates says nothing about moving
+  geometry. GPU parity (G0a/G0b) is unverified until run on a free device.
+
+## 10b. S3a — translation with refill (implemented on `claude/moving-bodies-s3a`)
+
+- Targets are enabled again (4a). `set_body(offset, vx, vy)` validates against
+  `applied`; a pending target blocks direct `LBMStepper.step(n > 0)` before any
+  launch; `run(n > 1)` with a target raises before mutation; `run(0)` never
+  consumes it; `run(1)` advances it.
+- Per advancing step, on one stream: upload the immutable FP64 records
+  `{c_old, c_new, r, u}` (only when changed) → M1 `MovingCircleCells` → M2
+  `MovingCircleLinks` (`u_w = u + omega x r` at the hit point) → static curved →
+  `OneStep` → swap → force region → sensors → synchronize → read `no_donor` →
+  commit (`applied := pending.offset`) → upload the hold record
+  (`c_old = c_new = applied`, `u = 0`) → synchronize. Hold steps launch no M1
+  and are the S2a path. Commit point: the advancing step-group sync plus a
+  zero `no_donor` count; a failure before it commits nothing. The hold-record
+  upload stages the next step after the commit: if it (or its sync) fails,
+  `applied` already matches the moved device geometry, but the Simulation is
+  still marked failed and refuses reuse. Any failure from the first upload on
+  marks the circles and the Simulation failed.
+- M1 classifies with the old/new predicates only (no flag reads). Covered
+  cells add raw `sum c G` / `sum G` of `G^{n-1}` to `cover_*` and become
+  `SOLID|OBSTACLE|BC_CURVED`. Uncovered cells: donors are fluid in both
+  geometries; `rho_bar` over all of them; NEQ from the donor with the largest
+  unnormalized `c·n > 0` (first direction wins ties, `n` from `c_new`);
+  `u_w` (translation + spin) at the cell position; all nine slots written;
+  raw `sum c G`, `sum G` of the refill go to `uncover_*`; no donor →
+  `f_eq(RHO, u_w)` plus `no_donor` (hard failure before commit); no NEQ donor
+  → `eq_only`.
+- `get_flags()` reads the device flags back (synchronized) when moving tables
+  exist; otherwise it returns the host array as before.
+- Not selected: the structural force. CME+node vs CME+Wen stay OPEN until X1
+  and G4 have run.
+
+## 11. Remaining decisions
+
+Structural RHS (section 6); motion-record layout; refill details; coupling
+scheme; benchmark definitions and digitized reference data; tolerances;
+execution/resource feasibility (Astra, pending); whether a quiescent domain
+(zero inlet velocity) runs cleanly in the current config.

docs/supported_settings.md

@@ -82,6 +82,13 @@ Tests: `tests/unit/test_jets.py`, `test_jets_review.py`, `test_shifted_jets.py`,
 - 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.
 
+## Moving circles (dense `Simulation`, uniform grid only)
+
+Translating circles with optional spin are supported on the dense double
+buffer D2Q9 FP32 path only (not on `FixedPatchStepper` or refined levels).
+API, supported/rejected modes and limits: `docs/moving_bodies.md`; stage-1
+evidence: `docs/validation/moving_bodies_stage1.md`.
+
 ## Not supported in this release
 
 3D, dynamic/automatic AMR (tagging, time-varying hierarchies beyond `remap_finest`),

docs/validation/duetsch_re100_kc5_protocol.md

@@ -0,0 +1,242 @@
+# Prescribed in-line oscillation: Dütsch Re 100 / KC 5 — PROTOCOL (review draft)
+
+Production under test: `claude/moving-bodies-s3a` at `653fd997` (unchanged).
+Primary source: Dütsch, Durst, Becker & Lienhart, J. Fluid Mech. 360, 249–271
+(1998), doi:10.1017/S002211209800860X. Source facts below were verified from
+the paper (Slack C0C78UFKGRM/1793335557.460509, TRON 1793356317–1793356724,
+page numbers given). Everything marked ENGINEERING is our a-priori choice,
+fixed before any benchmark result; it is not a paper uncertainty.
+
+## 0. Source facts (with provenance)
+
+- Motion (p.251): `x_c = -A sin(2 pi f t)`; paper phase phi = 0 is the mean
+  position moving left at `-U_max`. KC = 5 gives `A/D = 5/(2 pi) = .7957747`.
+- Start (p.254): the computation starts a quarter cycle before phi = 0, at
+  `x = +A` with zero velocity (phi = -90°).
+- Experiment (pp.252, 254–256): D = 10 mm, L = .65 m, tank 1.2 × .7 × .7 m,
+  rho = 998.2 kg/m³, mu = 1.00818 mPa·s, Re = 100, KC = 5; LDA with 1° phase
+  bins and 200 samples per node and degree; no quantified experimental error
+  recovered.
+- Profiles (Fig. 8, p.260): LAB-FIXED stations x1 = -6, 0, 6, 12 mm, i.e.
+  x/D = -.6, 0, .6, 1.2, at phi = 180°, 210°, 330°; u1 and u2 versus x2.
+- Original numerics (§2): cylinder-fixed accelerated frame (`x_i = x~_i +
+  x_i,s`, outer velocity `-u_c`, inertial source `-rho du_c/dt`), O-grid outer
+  diameter 120 D, illustrated 192 circumferential nodes, 720 steps/cycle; tank
+  influence neglected.
+- Force fit (verified): force ON THE BODY per unit span
+  `F1 = -0.5 rho D c_d xdot|xdot| - (pi/4) rho D² c_i xddot` with `x = -A sin phi`;
+  normalized by `0.5 rho D U_max²`: `c_d cos phi |cos phi| - (pi² c_i / KC) sin phi`.
+  `c_i` is the ADDED-MASS coefficient; total inertia `c_m = c_i + 1` is a
+  different convention and is not used.
+- Table 1 computed Morison coefficients (c_d, c_i) for 96 / 192 / 384 perimeter
+  nodes at dt/T = 1/720: (2.15, 1.42), (2.10, 1.45), (2.09, 1.45). These are
+  fitted computed coefficients, not a measured force and not an error bar. The
+  paper states the coarse direct force is closer to the finest direct force
+  than the Morison fit, but gives no waveform-error norm.
+
+## 1. Kinematics, time levels and phase bookkeeping
+
+- Our run is in the LAB frame: the circle moves, the fluid is initially at rest
+  (rho = 1, u = 0); no fictitious inertial source is added. Lab-fixed profile
+  stations are compared directly (no frame transform needed).
+- Geometry reference: the circle's base centre is the INITIAL position, the
+  right turning point `x_mean + A`; the declared offset box is x in [-2A, 0],
+  y = 0. The body is never teleported: offset 0 at s = 0.
+- Elapsed time s = n dt from the start. Analytic position relative to the mean
+  `x(s) = A cos(2 pi s / T)`, velocity `u(s) = -U_max sin(2 pi s / T)`; paper
+  phase `phi = (360 s / T - 90) mod 360`.
+- Step n moves from s_n to s_{n+1}: target offset `x(s_{n+1}) - A`; wall
+  velocity = the single-step interval average `(x(s_{n+1}) - x(s_n)) / dt`
+  (analytic, supplied, not differenced from stored offsets). The per-step
+  force of `run(1)` / `read_force(normalize=True)` is attributed to that same
+  interval.
+- Paper cycle k = 1, 2, ... spans `s in [T/4 + (k-1) T, T/4 + k T)`; the
+  initial quarter cycle (s < T/4) is cycle 0 and never scored. Every logged
+  sample carries (k, phi). Example: phi = 330° of cycle 1 is at s = 7T/6.
+- T is chosen as a multiple of 360 native steps, so phi = 180°, 210°, 330° fall
+  exactly on step boundaries and 1° bins hold whole steps.
+
+## 2. Resolution ladder (uniform grid, fixed Mach), ENGINEERING
+
+| D (cells) | T (steps) | U_max = 5 D / T | nu_lat = U_max D / 100 | tau (3 nu + .5) |
+|---|---|---|---|---|
+| 20 | 2,520 | .039683 | .0079365 | .5238 |
+| 40 | 5,040 | .039683 | .015873 | .5476 |
+| 80 | 10,080 | .039683 | .031746 | .5952 |
+
+- MRT collision. Mach fixed (Ma ≈ .0687); a separate Mach check at D = 40
+  with T = 10,080 (U_max halved, tau .5238) is labelled MACH and not part of the
+  ladder.
+- Per-step displacement ≤ U_max ≈ .04 cells (bound .5).
+
+## 3. Domain and boundaries (finite-domain reproduction), ENGINEERING
+
+The paper's 120 D O-grid is not reproduced; our rectangular box is a
+reproduction choice. The native dense channel (zero-velocity inlet,
+pressure-NEQ outlet, bounce-back y walls) is a finite-domain approximation,
+not infinite still fluid. The G4 x-periodic / y-slip override is a separately
+labelled sensitivity family and never mixed into the primary ladder. The
+runner owner confirms the zero-velocity inlet is supported as configured
+before any run.
+
+Order (closed):
+1. Smoke + ledger at D = 40, native BC, 40 D × 40 D (finite box).
+2. Domain sensitivity before any literature statement: same BC, D = 40,
+   L ∈ {20 D, 40 D, 60 D}; record the change in Fx waveform, c_d, c_i and the
+   scored profiles.
+3. Optional labelled BC sensitivity: one x-periodic / y-slip case at D = 40,
+   40 D; reported as a delta against native only.
+4. Only after step 2 passes: the D = 20 / 40 / 80 ladder on the chosen BC and
+   domain.
+
+Domain criteria (a-priori, ENGINEERING; separate from the Table 1 bands): the
+reference is 60 D at D = 40; 20 D and 40 D are compared with it on the common
+window (same cycle indices) and the common valid point set:
+- `RMS(Fx_L - Fx_60D) / F_ref ≤ .01` over the window (per-step waveforms);
+- `|c_d,L - c_d,60D| ≤ .02` and `|c_i,L - c_i,60D| ≤ .02` (window fits);
+- `max(|u_L - u_60D|, |v_L - v_60D|)` over common points `/ U_max ≤ .02`.
+The chosen domain is the smallest of {20 D, 40 D} passing all three; if
+neither passes, the domain verdict is FAIL and the ladder is not run.
+- Memory/runtime: measured by a smoke run before each new size; measurements
+  inform scheduling only, never tolerances.
+
+## 4. Observables (raw, per step, preserved)
+
+- `obs` Fx, Fy (CME) and all `MovingTables.DIAG` columns per step: CME,
+  CME + Wen and CME + cover − uncover reported separately; crossings, eq_only,
+  no_donor (no_donor must stay 0).
+- Velocity u1, u2 on lab-fixed lines x/D = -.6, 0, .6, 1.2 (relative to the
+  mean cylinder position) versus x2, at the scored phases. Lab frame
+  throughout; if any body-frame intermediate is used, position and velocity
+  are both transformed.
+- Sampling cost: raw force and diagnostics counters are read every step
+  (small). Flags and velocity fields are read only at the steps inside the
+  three prescribed 1° phase bins (φ ∈ [180, 181), [210, 211), [330, 331),
+  T/360 steps each) of the cycles needed for settling and scoring, plus
+  sparse declared audits; never every step.
+- Point set: fixed x2/D sample points per station, identical on every grid
+  and declared before running; per point the interpolation weights are
+  recorded; the scored set is the common subset valid on all compared grids
+  at that phase, with its coverage recorded; point sets never change silently.
+- Interpolation: bilinear on cell centres using only cells that are fluid at
+  that step (flags read back via `get_flags()`); weights renormalized over the
+  fluid corners; a sample with no fluid corner, or inside the circle at that
+  step, is MISSING and logged, never set to zero. One-degree bins keep valid
+  fluid weights. The numerical average need not mimic the 200 LDA samples.
+
+## 5. Periodic-regime gate (every case, before any statistic), ENGINEERING
+
+Ledger rows, same schema for every case: dx, dt (in D and T units); U_max, nu,
+Re, KC (lattice and nondimensional); T (native steps, nondimensional);
+duration (native steps, s/T, paper cycles); discard; accepted window; cycle
+ledger; verdict PASS or FAIL-CLOSED.
+
+Scales: `F_ref = 0.5 rho U_max² D`, `U_ref = U_max`; never a near-zero mean
+force as denominator.
+
+- Settling metrics, cycle k−1 → k, phase-aligned by step within the cycle
+  (error budget: one fifth of the tightest comparison band of the same
+  observable, so residual drift cannot obscure a domain or resolution pass):
+  - waveform `RMS(dFx) / F_ref ≤ .002`;
+  - `|d mean|`, `|d RMS|`, `|d peak|` of Fx, each `/ F_ref ≤ .002`;
+  - scored profiles (fluid-only) `|du| / U_max`, `|dv| / U_max ≤ .004` at the
+    three phases × four stations;
+  - Morison `|dc_d| ≤ .004`, `|dc_i| ≤ .004`.
+- Conservative comparison: every domain and cross-resolution criterion is
+  applied to `|difference| + drift_a + drift_b`, where drift is the largest
+  pair metric of that case inside the scored window.
+- These constants (protocol.py SETTLE, DOMAIN, CROSS) are frozen before any
+  physical result; no post-result loosening.
+- Rule: all metrics for N = 3 consecutive whole paper cycles → settled.
+
+Cycle indexing (worked example, binding). Paper cycle k spans
+`s/T in [0.25 + (k-1), 0.25 + k)`, i.e. φ0 → φ0; cycle 0 is the startup
+quarter `s/T < 0.25`. Pair p_k compares cycle k−1 with cycle k.
+
+- Discarded: cycles 0, 1, 2 (s/T < 2.25). Pairs are formed only between
+  cycles ≥ 3, so the first pair is p_4 (3 → 4).
+- Settling proof for a case: three consecutive pairs all pass; K_case = the
+  first cycle AFTER the last of those pairs. Earliest possible: pairs 3→4,
+  4→5, 5→6 pass ⇒ K_case = 7.
+- Common window: K = max over compared cases of K_case; every case scores the
+  same three complete cycles K, K+1, K+2 and must stay settled continuously:
+  every pair p_j for j = its own K_case .. K+2 must pass (including the wait
+  between its local settle and the common K), otherwise that case is
+  FAIL-CLOSED.
+- Cap: cycle k ends at s/T = k + 0.25, so the last admissible scored cycle is
+  11 (ends 11.25 T) and K ≤ 9. Examples: K = 7 → cycles 7–9 (ends 9.25 T);
+  K = 9 → cycles 9–11 (ends 11.25 T); any K_case > 9 → FAIL-CLOSED.
+- Run length: cases run sequentially; each runs to the end of cycle 11
+  (11.25 T: 28,350 / 56,700 / 113,400 steps for D = 20 / 40 / 80; the 12 T
+  cap is 30,240 / 60,480 / 120,960) and keeps its scalar and profile data, then
+  the common K is chosen. An unscorable partial cycle 12 is not run.
+- Profiles: an empty common valid point set is FAIL-CLOSED; coverage, missing
+  points, bin time weights (equal per step) and the original fluid corner
+  weight sums are reported.
+- The earlier G4 timing check (100 coarse vs 400 diffusive-fine steps) was a
+  matched short transient, not periodic evidence.
+
+## 6. Metrics and per-observable criteria (ENGINEERING, not paper uncertainty)
+
+Three criteria stay separate; the G4 same-grid 2% target is not reused.
+
+- Morison fit: least squares of the normalized per-step force over the
+  accepted window against the two basis functions, each averaged over its
+  single step interval, fixed paper phase, no free phase shift; c_d and
+  added-mass c_i per force candidate.
+- Cross-resolution: every scored observable's error against its reference must
+  decrease monotonically D20 → D40 → D80 (necessary, not sufficient).
+- Against Table 1 (computed fit, not measured force): at D ≥ 40,
+  `|c_d - 2.09| ≤ .15` and `|c_i - 1.45| ≤ .15`, and monotone.
+- Force waveform against its own Morison reconstruction: residual reported
+  only, no pass/fail (the paper reports fit error above its coarse numerical
+  error and gives no percentage).
+- Fig. 8 LDA profiles: QUALITATIVE ONLY. The original figure could not be
+  accessed or rendered; no digitized ordinates and no measurement uncertainty
+  exist. After a digitization with figure number, tool and uncertainty note:
+  `RMS(|du|, |dv|) / U_max ≤ .15` at D ≥ 40 and monotone; LDA error stays
+  UNQUANTIFIED and is stated with every comparison.
+- Fy sanity (not literature): `|mean Fy| / F_ref ≤ .05` in the accepted window.
+- No force candidate is selected for an RHS by these results; each is
+  reported.
+
+Superseded (earlier drafts): the velocity-jump start, guessed stations and
+phases, "C_M" for c_i, and the uncertainty wording; cycles 4–6, the 30-cycle
+cap and the earlier tolerance numbers.
+
+## 6b. Amendment: duration-only diagnostic (declared before the run)
+
+- Background: the D40 domain stage (20 D / 40 D / 60 D, 11.25 T each) failed
+  settling in every box (no window). That result stands.
+- One declared diagnostic: D = 40, 60 D box, from rest, through cycle 31
+  (157,500 steps = 31.25 T). Physics, settling tolerances, bands and
+  production unchanged; three proof pairs plus a continuously settled
+  K..K+2 with K ≤ 29.
+- Invocation: `run.py --D 40 --box 60 --cycles 31` then
+  `analyze.py --horizon 31`; the JSON records `horizon` and `horizon_mode`.
+  Without `--horizon` the analyzer is the original cap-11 scoring.
+- Failure at 31.25 T: report and stop; no automatic extension, matrix, D80
+  or VIV. A pass shows only that this box settles with time; it is not a
+  domain or literature pass.
+- The phase-locked high-frequency force component (residual of the mean
+  waveform after its Morison reconstruction, above 20/T) is reported per case
+  as unqualified; it needs separate qualification before any Morison or
+  literature statement.
+
+## 6a. Driver unit tests (CPU, before any run)
+
+- Phase/cycle arithmetic: s ↔ (k, φ), cycle boundaries, bin membership,
+  window/cap selection for K = 7, 8, 9, 10.
+- Solid-aware interpolation: all-fluid, partial-solid (renormalized weights),
+  no-fluid (MISSING) and inside-circle cases.
+- Interval-averaged Morison bases and the two-parameter fit on a synthetic
+  waveform with known c_d, c_i.
+
+## 7. Order and scope
+
+Protocol review → one-shot Dütsch driver (analytic `set_body` + `run(1)`,
+cycle ledger, lab-fixed fluid-only station sampler, two-basis Morison fit; no
+reusable runner until the first smoke shows shared helpers pay off; no
+production change) → smoke (memory/runtime) → domain sensitivity →
+ladder → physical-validation verdict → only then single-cylinder VIV. No AMR,
+no pinball, no manuscript work.

docs/validation/moving_bodies_stage1.md

@@ -0,0 +1,46 @@
+# Moving circles — stage-1 evidence (development level)
+
+Owner criterion (Yanqi via TRON): prescribed motion and one free VIV case both
+"reasonably close" to a predeclared reference = development-stage success.
+This is practical closeness, not a formal validation claim. Every number
+below is from Astra's receipts as posted in Slack C0C78UFKGRM thread
+1793335557.460509; raw outputs stay on Horsea under `/tmp/celeris-results-*`
+and the Mac evidence directory (not in git).
+
+## Code
+
+- Production: `src/` identical to `653fd997` (slices S1 `983020b6`,
+  S2a `b920a303`, S3a `653fd997`). CPU suites and GPU hold/crossing gates
+  passed on those slices (G0a/G0b population-bitwise; X1 crossing ledger).
+- Research drivers: `research/duetsch_re100_kc5/` (`dd37883d`, capture
+  `a0aea3b9`) and `research/viv_re150/` (`fb507aa1`), run as committed.
+
+## Prescribed in-line oscillation (Dütsch et al. 1998, Re 100, KC 5)
+
+- Protocol: `docs/validation/duetsch_re100_kc5_protocol.md`.
+- Frozen settling gate (.002 F_ref waveform): **FAILED** and kept on record:
+  D40 domain stage (20/40/60 D, 11.25 T) and the 60 D duration diagnostic
+  (31.25 T, 0/28 pairs; last waveform drift .00613 F_ref).
+- Unscored late-cycle CME fits c_d ≈ 2.02–2.05, c_i ≈ 1.46–1.48 vs the
+  paper's computed (2.09, 1.45); fields clean and symmetric (owner view).
+  The owner accepts ~0.61 % cycle drift at D40 for this stage; the gate is
+  not re-scored.
+- Fig. 8 LDA profiles: qualitative only (no digitized ordinates).
+
+## Free transverse VIV (Kolahdouz §4.1.1 setup, Qin §4.5 target)
+
+- Predeclaration: `docs/validation/viv_re150_predeclare.md` (agreed at
+  `1abfe954` under its former name `leontini_viv_predeclare.md`); run at `fb507aa1`, single case, D = 40, 75 D × 60 D.
+- Result: status `scored`, 336,384 steps (t U/D = 336.4); A_max = .5464 D vs
+  .520 D (+5.1 %, inside the declared ±10 % band); mean half peak-to-peak
+  .5448 D; f/f_n = .955; block drifts .78/.29/.18 %, last-five spreads
+  .15/.11/.10 %; finite, no_donor = 0, no seed; 337.7 s, ~1.0 ms/step.
+
+## Limitations (binding)
+
+- One resolution (D40) per case; no grid or time convergence.
+- Structural RHS = CME + Wen is a theory-motivated stage choice; CME-only
+  and node-impulse variants were not run as RHS; no force law is validated.
+- Boundary mismatches: NEQ outlet with backflow clamp vs traction outlet;
+  finite box; the strict Dütsch settling failure is unexplained.
+- No mass correction at curved walls; ~1 ms/step host-coupled overhead.

docs/validation/viv_re150_predeclare.md

@@ -0,0 +1,148 @@
+# Single-cylinder free transverse VIV, Re 150 (Kolahdouz/Qin) — PREDECLARATION (agreed at 1abfe954)
+
+(File renamed from `leontini_viv_predeclare.md`; the Leontini Re 200 case is only the queued second case below.)
+
+Stage goal (Yanqi via TRON): prescribed Dütsch case + one VIV case both
+"reasonably close" to a predeclared reference = development-stage success, then
+cleanup. The frozen Dütsch settling failure (0/28 pairs at 31.25 T) stays on
+record. Practical closeness is not a formal validation claim. Agreed by
+Claude, Grok and Astra at 1abfe954; implemented in research/viv_re150/.
+
+## Primary case (one case)
+
+- Reference: Qin et al., arXiv:2003.12186, §4.5 (maximum amplitudes at
+  U_red = 3…8: .075, .551, .520, .459, .370, .084 D in the text, as quoted by
+  Grok/Astra) for the target; setup from Kolahdouz et al., arXiv:2003.12046,
+  §4.1.1 (read 2026-10-30 via ar5iv): U* sweep 3–8 with amplitudes only in
+  Fig. 3(b) (no text values), domain [−30, 45] D × [−30, 30] D with the
+  cylinder "initially at rest and centered at the origin", uniform inflow on
+  the left, zero normal traction and tangential velocity at the outlet, zero
+  normal velocity and tangential traction on y = ±30 D; no initial
+  perturbation and no total simulated time stated.
+- Re = 150, U* = U/(f_n D) = 5, m/(rho D²) = 2 (m* = rho_s/rho_f = 8/pi),
+  zeta = 0, f_n = sqrt(K/M)/(2 pi) in vacuum. Transverse DOF only.
+- Target: A_max = .520 D (peak amplitude, Qin §4.5). Multi-code reference
+  (Kolahdouz ILE-NS, Qin II-LBM). Reference uncertainty: not stated; the
+  spread between codes is not quantified here.
+
+## Our reproduction (declared differences)
+
+- D = 40, MRT, dense double buffer; U_lat = .04, nu = U D / 150 = .010667,
+  tau = .532.
+- Box [0, 75 D] × [0, 60 D] (3000 × 2400) with the cylinder centre at
+  (30 D, 30 D): 30 D from the inlet, 45 D from the outlet, centred in y
+  (Kolahdouz §4.1.1). Qin's own box ([0, 40 D] × [0, 20 D], centre (10 D, 10 D))
+  is the target paper's, not ours.
+- Boundaries: uniform Zou–He inlet, NEQ outlet (rho = 1, backflow clamp),
+  free-slip y walls. Kolahdouz uses a traction outlet: declared mismatch.
+- Qin's own VIV box (40 D × 20 D) is not used; a smaller box would be a
+  declared cost cut with more blockage, not "the same case".
+- Allowed y offset ±1.5 D; peak transverse speed ≈ .026 cells/step (bound .5).
+
+## Structure, coupling and time levels
+
+- M = 2 rho D² (lattice rho = 1), f_n = U/(5 D) = 2e-4 per step, K = M (2 pi f_n)²,
+  zeta = 0. Equation of motion uses the structural mass only.
+- Per-step sequence (binding): known (y_n, v_n) and the last completed force
+  F_last → candidate (y_{n+1}, v_{n+1}) by the update below → `set_body` with
+  offset y_{n+1} and wall velocity (y_{n+1} − y_n)/dt with lattice dt = 1 (interval average; a
+  different quantity from the endpoint v_{n+1}) → `run(1)` → only on success:
+  commit y_n ← y_{n+1}, v_n ← v_{n+1}, F_last ← force read for that step (failure
+  semantics: see the window section). Whether the
+  measured force represents the interval's start, midpoint or end is not
+  asserted; the one-step lag is declared, not corrected.
+- Initial state: fluid initialized by `Simulation.initialize()` to the uniform
+  inlet velocity U everywhere (the code's actual initial condition; the
+  source gives no fluid initial condition), body at rest at the declared
+  centre, y_0 = v_0 = 0, F_last = 0.
+- Structural update over one step with constant force F = F_last (exact
+  harmonic solution, zeta = 0): y_e = F/K, w = 2 pi f_n,
+  y^{n+1} = y_e + (y^n − y_e) cos w + (v^n / w) sin w,
+  v^{n+1} = −(y^n − y_e) w sin w + v^n cos w.
+- Primary RHS (single coupled run): CME + Wen (theory-motivated stage choice:
+  Galilean-invariant link correction; G4 could not separate it from CME).
+  Raw CME and the node terms are logged as diagnostics of that trajectory;
+  the node impulse is not added. A run with CME-only as RHS is a separate,
+  labelled sensitivity case, decided separately. Neither RHS is claimed proven.
+
+## Window, failure semantics, acceptance (engineering, development stage)
+
+Clocks: lattice dt = 1; T_n = 1/f_n = 5,000 steps. Response cycles are
+counted from the measured signal; T_n is used only for the seed check.
+
+- Start: body at rest at the declared centre (the only initial condition the
+  source states), y_0 = v_0 = 0, F_last = 0; fluid uniform at U (as
+  initialized by the code; our choice, not the source's).
+- Seed (conditional, one time, declared): at step n_seed = 200,000
+  (t = 40 T_n), if max |y_t| over states t in [175,000, 200,000) is below
+  .01 D, then
+  in that step, after the check and before the candidate update, set
+  v_n += 2 pi f_n (.01 D) (F_last unchanged) and proceed normally; the
+  geometry moves continuously through the update. `seed_applied`, step and
+  size are logged; never repeated or changed.
+- Cycle boundary (discrete, fixed threshold): step n closes a cycle iff
+  y[n−1] < 0 and y[n] ≥ 0 (upward crossing of the equilibrium y = 0);
+  y_0 = 0 is not a crossing; no boundary fewer than 2 samples after the
+  previous one.
+- Per cycle: positive peak max(y), negative peak min(y), mean offset
+  (time-mean of y), amplitude a = (max − min)/2 (the only amplitude used for
+  settling).
+- Eligibility: a completed cycle is counted (toward the settling proof and
+  the 150 budget) only if a ≥ .01 D; ineligible cycles are logged, never
+  counted, so near-zero motion cannot settle or pass.
+- Seed reset: if the seed is applied, the incomplete cycle at n_seed is
+  discarded and the settling proof starts empty; the 150 budget and the
+  native cap keep running from t = 0.
+- Windows: adjacent non-overlapping blocks of 10 counted cycles;
+  W_k = mean amplitude of block k (W_k ≥ .01 D by eligibility, so no zero
+  denominator).
+- Block rule R(k), k ≥ 2: |W_k − W_{k−1}| / W_{k−1} ≤ .02 and, for the last 5
+  cycles of block k, max_i |a_i − ā_5| / ā_5 ≤ .01 with ā_5 their mean.
+- Settled at the end of block k when R(k) holds. Scoring = the next two
+  blocks k+1, k+2 (20 counted cycles); both must satisfy R. If one fails,
+  that block becomes the new reference: the settling proof restarts from it
+  and continues within the caps (deterministic; no other retry). A pass
+  requires one complete stable 20-cycle scoring window before a cap; success
+  stops after its 20th cycle.
+- Caps (both always armed; the first hit wins and is reported): 150 counted
+  response cycles including the 20 scoring cycles (so settling must complete
+  by counted cycle 130) → `timeout_response_cycles`; 1,000,000 native steps
+  (200 T_n) → `timeout_native_steps`.
+- Durations reported: total steps, t U/D, counted and uncounted cycles,
+  measured T_resp (mean boundary interval); N_resp / f_n only as a labelled
+  secondary clock.
+- Growth is not a failure: initial VIV growth is physical. Checked every
+  step (FAIL-CLOSED): non-finite y, v or force; |y| > 1.0 D (the tighter
+  gate; about twice the largest reference peak, .551 D) or the ±1.5 D offset
+  box reached; no_donor > 0; a failed upload/step/sync.
+- On any failure the driver stops and reports; it never retries,
+  sub-iterates, retunes the RHS or parameters, or starts a second case.
+  Device-side failures (upload/step/sync, no_donor) mark the Simulation
+  failed through the existing lifecycle; input rejection by `set_body`
+  (offset box, speed, step bound) and timeouts end the driver run without
+  that mark.
+- Target metric over the 20 scoring cycles: A_max/D = max over those cycles
+  of max(|positive peak|, |negative peak|) about y = 0 (Qin reports "maximum
+  amplitude"); also reported: mean amplitude, positive and negative peaks,
+  mean offset, f/f_n (no target).
+- Acceptance: |A_max − .520 D| ≤ .052 D (±10 %), stated together with the
+  boundary mismatch and the absence of a quoted reference uncertainty. A pass
+  is "reasonably close" for the stage: not grid convergence, not force-RHS
+  validation, and it does not touch the Dütsch settling record.
+- Driver reads force and the small diagnostics per step only; field reads
+  only at a few predeclared snapshots. No runtime claim: there is no measured
+  timing on this grid yet (the D40/60D receipt is a different, sampled case).
+
+## Plumbing smoke (not the benchmark)
+
+`run.py --smoke --D 20 --steps 32` runs exactly 32 steps of the same BC
+package and coupling loop (no seed, settle or score; never scored);
+status `smoke_ok` iff every step is finite, no_donor stays 0 and the body
+stays inside its box. The physical case is only the default invocation
+(`--D 40`, no `--smoke`).
+
+## Queued, not in this stage
+
+Leontini et al. JFS 22 (2006) Re = 200, m* = 10, zeta = 0.01, U* = 5.0 (needs
+the owners' c_crit convention and a Fig. 1 digitization). D80, literature
+claims, pinball, AMR, BC redesign, threshold changes.

research/duetsch_re100_kc5/analyze.py

@@ -0,0 +1,224 @@
+"""Ledger, settling, common window and Morison fits for Dütsch cases (numpy only).
+
+    python analyze.py CASE_DIR [CASE_DIR ...]   # cases of one comparison
+"""
+from __future__ import annotations
+
+import json
+import math
+import os
+import sys
+
+import numpy as np
+
+import protocol as p
+
+
+def load(path):
+    with open(os.path.join(path, "case.json")) as fh:
+        case = json.load(fh)
+    raw = np.load(os.path.join(path, "raw.npz"))
+    case.update(force=raw["force"], diag=raw["diag"], samples=raw["samples"], path=path)
+    return case
+
+
+def cycle_slices(case):
+    """{k: slice of step indices m whose interval [m, m+1] lies in paper cycle k}."""
+    T, q = case["T"], case["T"] // 4
+    return {k: slice(q + (k - 1) * T, q + k * T)
+            for k in range(1, case["cycles"] + 1) if q + k * T <= len(case["force"])}
+
+
+def coarse_wave(case, k, r=1):
+    """Normalized per-step Fx of cycle k, averaged over r native steps per sample."""
+    f = case["force"][cycle_slices(case)[k], 0] / case["F_ref"]
+    return f.reshape(-1, r).mean(axis=1)
+
+
+def profiles(case, k):
+    """{(phase, station, x2): (u, v)} of cycle k, time-averaged over the bin steps
+    (equal weights per step) from valid samples only."""
+    s = case["samples"]
+    acc = {}
+    for _, _, ph, xs, x2, u, v, _ in s[s[:, 1] == k]:
+        if not (math.isnan(u) or math.isnan(v)):
+            acc.setdefault((ph, xs, x2), []).append((u, v))
+    return {key: tuple(np.mean(vals, axis=0)) for key, vals in acc.items()}
+
+
+def coverage(case, k):
+    s = case["samples"]
+    rows = s[s[:, 1] == k]
+    missing = int(np.isnan(rows[:, 5]).sum())
+    return dict(samples=len(rows), missing=missing, bin_steps=len(set(rows[:, 0])),
+                min_fluid_weight=float(np.nanmin(np.where(rows[:, 7] > 0, rows[:, 7], np.nan)))
+                if len(rows) else math.nan)
+
+
+def common_points(dicts):
+    keys = set(dicts[0])
+    for d in dicts[1:]:
+        keys &= set(d)
+    return sorted(keys)
+
+
+def candidates(case):
+    """Per-step Fx of each reported force candidate (none is selected as an RHS)."""
+    d = case["diag"]
+    return {"cme": d[:, 0], "cme_wen": d[:, 0] + d[:, 2], "cme_node": d[:, 0] + d[:, 6] - d[:, 9]}
+
+
+def cycle_morison(case, ks, fx=None):
+    T = case["T"]
+    fx = case["force"][:, 0] if fx is None else fx
+    idx = np.concatenate([np.arange(len(fx))[cycle_slices(case)[k]] for k in ks])
+    b = np.array([p.interval_bases(int(m), T) for m in idx])
+    return p.morison_fit(fx[idx] / case["F_ref"], b[:, 0], b[:, 1])
+
+
+def pair_metrics(case, k):
+    a, b = coarse_wave(case, k - 1), coarse_wave(case, k)
+    pa, pb = profiles(case, k - 1), profiles(case, k)
+    common = common_points([pa, pb])  # empty set -> inf -> pair fails (FAIL-CLOSED)
+    prof = max((max(abs(pa[c][0] - pb[c][0]), abs(pa[c][1] - pb[c][1])) for c in common),
+               default=math.inf) / case["u_max"]
+    (cd0, ci0), (cd1, ci1) = cycle_morison(case, [k - 1]), cycle_morison(case, [k])
+    m = dict(wave=float(np.sqrt(np.mean((b - a) ** 2))),
+             scalar=float(max(abs(b.mean() - a.mean()), abs(np.sqrt(np.mean(b * b)) - np.sqrt(np.mean(a * a))),
+                              abs(np.abs(b).max() - np.abs(a).max()))),
+             profile=float(prof), morison=float(max(abs(cd1 - cd0), abs(ci1 - ci0))),
+             profile_points=len(common))
+    m["pass"] = all(m[key] <= tol for key, tol in p.SETTLE.items())
+    return m
+
+
+def hf_component(case, ks):
+    """Unqualified phase-locked high-frequency force component (reported, not checked):
+    mean CME waveform over cycles ks minus its two-basis Morison reconstruction,
+    split at 20/T; cycle differencing does not remove it."""
+    T = case["T"]
+    if not ks:
+        return dict(label="unqualified phase-locked HF force component, not checked", cycles=[])
+    mean = np.mean([coarse_wave(case, k) for k in ks], axis=0)
+    c_d, c_i = cycle_morison(case, ks)
+    q = T // 4
+    b = np.array([p.interval_bases(q + m, T) for m in range(T)])
+    resid = mean - (c_d * b[:, 0] - (np.pi ** 2 * c_i / p.KC) * b[:, 1])
+    spec = np.fft.rfft(resid)
+    high = spec.copy()
+    high[:21] = 0.0
+    energy = one_sided_energy(spec, T)
+    return dict(label="unqualified phase-locked HF force component, not checked",
+                cycles=list(ks), hf_rms_over_F_ref=float(np.sqrt(np.mean(np.fft.irfft(high, T) ** 2))),
+                hf_energy_fraction=float(energy[21:].sum() / max(energy.sum(), 1e-300)),
+                top_harmonics=[int(j) for j in np.argsort(energy[21:])[::-1][:5] + 21])
+
+
+def one_sided_energy(spec, n):
+    """Parseval-consistent energy per rfft bin: interior bins count twice, DC and
+    (for even n) Nyquist once."""
+    w = np.full(len(spec), 2.0)
+    w[0] = 1.0
+    if n % 2 == 0:
+        w[-1] = 1.0
+    return w * np.abs(spec) ** 2
+
+
+def ledger(case, horizon=p.LAST_SCORED):
+    ks = [k for k in sorted(cycle_slices(case)) if k <= horizon]
+    pairs = {k: pair_metrics(case, k) for k in ks if k - 1 > p.DISCARD}
+    return pairs, p.settled_start({k: v["pass"] for k, v in pairs.items()})
+
+
+def main(argv):
+    """argv: CASE_DIR ... [--reference CASE_DIR]; the reference defaults to the
+    largest D (resolution ladder); domain runs name the 60 D case explicitly."""
+    ref_path = None
+    if "--reference" in argv:
+        i = argv.index("--reference")
+        ref_path, argv = argv[i + 1], argv[:i] + argv[i + 2:]
+    horizon, explicit = p.LAST_SCORED, "--horizon" in argv  # default: original scoring
+    if explicit:
+        i = argv.index("--horizon")
+        horizon, argv = int(argv[i + 1]), argv[:i] + argv[i + 2:]
+    paths = argv if ref_path is None or ref_path in argv else argv + [ref_path]
+    cases = [load(path) for path in paths]
+    for c in cases if explicit else ():  # complete cycles 1..N; never pad or shift
+        if c["cycles"] < horizon or len(c["force"]) < round((0.25 + horizon) * c["T"]):
+            raise SystemExit(f"{c['path']}: run does not contain complete cycles 1..{horizon}")
+    ledgers = [ledger(c, horizon) for c in cases]
+    window = p.common_window([k for _, k in ledgers],
+                             [{k: v["pass"] for k, v in pairs.items()} for pairs, _ in ledgers],
+                             last_scored=horizon)
+    report = dict(window=window, horizon=horizon, cases=[],
+                  horizon_mode="default-cap" if horizon == p.LAST_SCORED else
+                  "extended duration diagnostic (declared amendment, D40/60D only)")
+    for case, (pairs, k_case) in zip(cases, ledgers):
+        limit = round((0.25 + horizon) * case["T"])  # events inside the horizon only
+        entry = {key: case[key] for key in ("path", "D", "T", "box", "n", "u_max", "nu", "tau", "A",
+                                            "steps", "cycles", "F_ref")}
+        entry.update(duration_T=case["steps"] / case["T"], K_case=k_case, pairs=pairs,
+                     coverage={k: coverage(case, k) for k in sorted(cycle_slices(case))
+                               if p.DISCARD < k <= horizon},
+                     no_donor=float(case["diag"][:limit, 13].sum()),
+                     eq_only=float(case["diag"][:limit, 12].sum()),
+                     hf_component=hf_component(case, window or tuple(
+                         [k for k in sorted(cycle_slices(case)) if p.DISCARD < k <= horizon][-3:])))
+        if window:  # residual drift inside the scored window (pairs K..K+2)
+            entry["window_drift"] = {key: max(pairs[k][key] for k in window)
+                                     for key in ("wave", "profile", "morison")}
+            entry["morison_obs"] = cycle_morison(case, window)
+            entry["morison"] = {name: cycle_morison(case, window, fx)
+                                for name, fx in candidates(case).items()}
+            entry["fy_mean"] = float(np.mean(np.concatenate(
+                [case["force"][cycle_slices(case)[k], 1] for k in window])) / case["F_ref"])
+        report["cases"].append(entry)
+    if window and len(cases) > 1:  # cross-resolution waveform against the finest case
+        fine = (next(c for c in cases if c["path"] == ref_path) if ref_path
+                else max(cases, key=lambda c: c["D"]))
+        report["reference"] = fine["path"]
+        ref = np.concatenate([coarse_wave(fine, k) for k in window])
+        for case, entry in zip(cases, report["cases"]):
+            r = fine["T"] // case["T"]  # 1 for equal-D domain runs
+            ref_c = ref.reshape(-1, r).mean(axis=1)
+            own = np.concatenate([coarse_wave(case, k) for k in window])
+            entry["wave_rms_vs_finest"] = float(np.sqrt(np.mean((own - ref_c) ** 2)))
+        for k in window:  # profiles on the common valid point set of all compared cases
+            per_case = [profiles(c, k) for c in cases]
+            keys = common_points(per_case)
+            report.setdefault("common_profile_points", {})[k] = len(keys)
+            if not keys:
+                report["verdict"] = "FAIL-CLOSED: empty common profile set"
+                continue
+            fine_p = per_case[cases.index(fine)]
+            for case, entry, prof in zip(cases, report["cases"], per_case):
+                d = max(max(abs(prof[key][0] - fine_p[key][0]), abs(prof[key][1] - fine_p[key][1]))
+                        for key in keys) / case["u_max"]
+                entry.setdefault("profile_max_vs_finest", {})[k] = float(d)
+        ref_entry = report["cases"][cases.index(fine)]
+        for entry in report["cases"]:  # conservative: difference + both drifts
+            if entry is ref_entry:
+                continue
+            drift = {key: entry["window_drift"][key] + ref_entry["window_drift"][key]
+                     for key in ("wave", "profile", "morison")}
+            dm = max(abs(entry["morison"]["cme"][0] - ref_entry["morison"]["cme"][0]),
+                     abs(entry["morison"]["cme"][1] - ref_entry["morison"]["cme"][1]))
+            entry["conservative"] = dict(
+                wave=entry["wave_rms_vs_finest"] + drift["wave"],
+                profile=max(entry.get("profile_max_vs_finest", {}).values(), default=math.inf)
+                + drift["profile"],
+                morison_cme=dm + drift["morison"])
+            bands = p.DOMAIN if ref_path else p.CROSS  # domain runs name the 60 D reference
+            c = entry["conservative"]
+            entry["pass_scope"] = (
+                ("wave+profile+morison_cme" if "morison" in bands else "wave+profile")
+                + ": conservative (|diff| + both window drifts) on the obs/CME Fx waveform and "
+                "simulation-to-simulation profiles; CME+Wen and CME+node reported, not checked; "
+                "no Fig. 8 / literature verdict")
+            entry["pass"] = (c["wave"] <= bands["wave"] and c["profile"] <= bands["profile"]
+                             and ("morison" not in bands or c["morison_cme"] <= bands["morison"]))
+    print(json.dumps(report, indent=1, default=float))
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])

research/duetsch_re100_kc5/capture.py

@@ -0,0 +1,52 @@
+"""Research-only field capture helpers for the Dütsch driver (numpy only).
+
+Snapshots are taken at the first step of the scored phase bins in declared
+cycles: a near-body crop at full resolution and a fluid-weighted block-mean
+downsample of the whole domain; plus scalar trends at every bin read.
+"""
+from __future__ import annotations
+
+import numpy as np
+
+CROP_X, CROP_Y, DOWN = 8.0, 6.0, 8      # crop half-widths in D; downsample factor
+STRIP = 2.0                             # inlet/outlet strip width in D
+
+
+def crop_box(xm, ym, D, n, body_extent):
+    """Inclusive integer crop (x0, x1, y0, y1); fail closed if it leaves the domain
+    interior or does not contain the body's swept extent (x_lo, x_hi, y_lo, y_hi)."""
+    x0, x1 = int(round(xm - CROP_X * D)), int(round(xm + CROP_X * D))
+    y0, y1 = int(round(ym - CROP_Y * D)), int(round(ym + CROP_Y * D))
+    if x0 < 1 or y0 < 1 or x1 > n - 2 or y1 > n - 2:
+        raise ValueError("capture crop leaves the domain interior")
+    bx0, bx1, by0, by1 = body_extent
+    if not (x0 <= bx0 and bx1 <= x1 and y0 <= by0 and by1 <= y1):
+        raise ValueError("capture crop clips the body's swept extent")
+    return x0, x1, y0, y1
+
+
+def downsample(field, fluid, f=DOWN):
+    """Fluid-weighted f x f block means; NaN where a block has no fluid cell."""
+    ny, nx = field.shape
+    h, w = ny // f, nx // f
+    v = np.where(fluid, field, 0.0)[:h * f, :w * f].reshape(h, f, w, f).sum(axis=(1, 3))
+    c = fluid[:h * f, :w * f].reshape(h, f, w, f).sum(axis=(1, 3))
+    with np.errstate(invalid="ignore", divide="ignore"):
+        return np.where(c > 0, v / np.maximum(c, 1), np.nan).astype(np.float32)
+
+
+def fluid_mean(field, fluid, xs=slice(None), ys=slice(None)):
+    m = fluid[ys, xs]
+    return float(field[ys, xs][m].mean()) if m.any() else float("nan")
+
+
+def trend_row(s, k, ph, rho, ux, uy, fluid, D, n, crop):
+    """(s, cycle, phase, <rho>, <ux>, <uy>, <rho>_crop, inlet <rho>, <ux>, outlet <rho>, <ux>)."""
+    w = max(1, int(round(STRIP * D)))
+    x0, x1, y0, y1 = crop
+    cx, cy = slice(x0, x1 + 1), slice(y0, y1 + 1)
+    inlet, outlet, inner = slice(1, 1 + w), slice(n - 1 - w, n - 1), slice(1, n - 1)
+    return (s, k, ph, fluid_mean(rho, fluid), fluid_mean(ux, fluid), fluid_mean(uy, fluid),
+            fluid_mean(rho, fluid, cx, cy),
+            fluid_mean(rho, fluid, inlet, inner), fluid_mean(ux, fluid, inlet, inner),
+            fluid_mean(rho, fluid, outlet, inner), fluid_mean(ux, fluid, outlet, inner))

research/duetsch_re100_kc5/protocol.py

@@ -0,0 +1,129 @@
+"""Pure arithmetic of the Dütsch Re 100 / KC 5 protocol (numpy only, no CUDA).
+
+docs/validation/duetsch_re100_kc5_protocol.md is the contract: elapsed time s
+in native steps from the right turning point, paper phase
+phi = (360 s / T - 90) mod 360, paper cycle k >= 1 spans
+s/T in [0.25 + (k-1), 0.25 + k); cycle 0 is the startup quarter.
+"""
+from __future__ import annotations
+
+import math
+
+import numpy as np
+
+KC, RE = 5.0, 100.0
+STATIONS = (-0.6, 0.0, 0.6, 1.2)          # lab-fixed x/D from the mean position
+PHASES = (180.0, 210.0, 330.0)            # degrees; bins [p, p + 1)
+X2 = tuple(np.round(np.arange(-1.5, 1.5001, 0.05), 10))  # declared x2/D points
+DISCARD, LAST_SCORED, N_PAIRS = 2, 11, 3   # cycles 0..2 discarded, cap 12 T
+# A-priori bands. Settling is one fifth of the tightest comparison band of the
+# same observable, and comparisons add both cases' residual window drift
+# (conservative: |difference| + drift_a + drift_b <= band).
+DOMAIN = dict(wave=.01, morison=.02, profile=.02)  # vs the 60 D reference at D = 40
+CROSS = dict(wave=.02, profile=.02)                # D40 vs D80
+SETTLE = dict(wave=.002, scalar=.002, profile=.004, morison=.004)
+
+
+def amplitude(D):
+    return KC * D / (2.0 * math.pi)
+
+
+def position(s, T, A):
+    """Centre position relative to the mean: x = A cos(2 pi s / T), evaluated from the
+    native step modulo T so every cycle repeats the same geometry bit for bit."""
+    return A * math.cos(2.0 * math.pi * (int(s) % T) / T)
+
+
+def phase(s, T):
+    """Paper phase in degrees from the native step modulo T (the unwrapped cycle
+    index is kept separately by ``cycle``)."""
+    return (360.0 * (int(s) % T) / T - 90.0) % 360.0
+
+
+def cycle(s, T):
+    return 0 if s < 0.25 * T else int(math.floor(s / T - 0.25)) + 1
+
+
+def bin_phase(s, T):
+    """Scored phase whose 1-degree bin [p, p + 1) contains time s, else None."""
+    phi = phase(s, T)
+    for p in PHASES:
+        if p <= phi < p + 1.0:
+            return p
+    return None
+
+
+def interval_bases(n, T, points=16):
+    """Single-step interval averages over [n, n + 1] of cos phi |cos phi| and sin phi
+    (phi in radians = 2 pi s / T - pi / 2), Gauss-Legendre quadrature."""
+    x, w = np.polynomial.legendre.leggauss(points)
+    s = int(n) % T + 0.5 * (x + 1.0)  # periodic: identical bases in every cycle
+    phi = 2.0 * np.pi * s / T - 0.5 * np.pi
+    c = np.cos(phi)
+    return 0.5 * float(np.sum(w * c * np.abs(c))), 0.5 * float(np.sum(w * np.sin(phi)))
+
+
+def morison_fit(f_norm, b1, b2):
+    """Least squares of f_norm = c_d b1 - (pi^2 c_i / KC) b2 (paper phase, no shift)."""
+    a = np.column_stack([b1, -(math.pi ** 2 / KC) * np.asarray(b2)])
+    (c_d, c_i), *_ = np.linalg.lstsq(a, np.asarray(f_norm), rcond=None)
+    return float(c_d), float(c_i)
+
+
+def inside_circle(x, y, centre, radius):
+    return (x - centre[0]) ** 2 + (y - centre[1]) ** 2 < radius * radius
+
+
+def sample(field, fluid, x, y, centre, radius):
+    """Profile sample: MISSING if the exact point is inside the body (checked before
+    any corner interpolation), else ``bilinear_fluid``."""
+    if inside_circle(x, y, centre, radius):
+        return None, (), 0.0
+    return bilinear_fluid(field, fluid, x, y)
+
+
+def bilinear_fluid(field, fluid, x, y):
+    """Bilinear value at (x, y) in cell coordinates from fluid cells only.
+
+    Returns (value, ((ix, iy, weight), ...), fluid_weight_sum) with weights
+    renormalized over the fluid corners and the original sum of their bilinear
+    weights, or (None, (), 0.0) when no corner is fluid (MISSING, never zero).
+    """
+    x0, y0 = int(math.floor(x)), int(math.floor(y))
+    fx, fy = x - x0, y - y0
+    corners = ((x0, y0, (1 - fx) * (1 - fy)), (x0 + 1, y0, fx * (1 - fy)),
+               (x0, y0 + 1, (1 - fx) * fy), (x0 + 1, y0 + 1, fx * fy))
+    used = [(i, j, w) for i, j, w in corners if w > 0.0 and fluid[j, i]]
+    total = sum(w for _, _, w in used)
+    if total == 0.0:
+        return None, (), 0.0
+    used = tuple((i, j, w / total) for i, j, w in used)
+    return float(sum(w * field[j, i] for i, j, w in used)), used, float(total)
+
+
+def settled_start(pairs_pass):
+    """K_case from {k: pass of pair (k-1 -> k)}: first cycle after three consecutive
+    passing pairs among cycles > DISCARD, or None."""
+    run = 0
+    for k in sorted(pairs_pass):
+        if k - 1 <= DISCARD:
+            continue
+        run = run + 1 if pairs_pass[k] else 0
+        if run == N_PAIRS:
+            return k + 1
+    return None
+
+
+def common_window(k_cases, pairs_pass_by_case, last_scored=LAST_SCORED):
+    """Common scored cycles K..K+2 with K = max K_case, or None (FAIL-CLOSED) when a
+    case never settled, K + 2 exceeds the cap, or a case fails any pair p_j for
+    j = its own K_case .. K + 2 (continuous settling, including the wait for K)."""
+    if any(k is None for k in k_cases):
+        return None
+    K = max(k_cases)
+    if K + 2 > last_scored:
+        return None
+    for k_case, pairs in zip(k_cases, pairs_pass_by_case):
+        if not all(pairs.get(j, False) for j in range(k_case, K + 3)):
+            return None
+    return K, K + 1, K + 2

research/duetsch_re100_kc5/run.py

@@ -0,0 +1,133 @@
+"""One-shot Dütsch Re 100 / KC 5 prescribed in-line oscillation driver.
+
+Protocol: docs/validation/duetsch_re100_kc5_protocol.md. Native dense channel
+(zero-velocity inlet, pressure-NEQ outlet, bounce-back y walls), MRT, lab frame.
+Writes raw per-step force/diagnostics and phase-bin profile samples to --out
+(outside the checkout); analysis is in analyze.py. No production change.
+
+    python run.py --D 40 --box 40 --cycles 11 --out /path/outside/checkout
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import math
+import os
+import tempfile
+
+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))
+    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():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--D", type=int, required=True)
+    ap.add_argument("--box", type=float, default=40.0, help="box side in D")
+    ap.add_argument("--T", type=int, default=None, help="period in steps (multiple of 360)")
+    ap.add_argument("--cycles", type=int, default=p.LAST_SCORED, help="run to the end of this cycle")
+    ap.add_argument("--out", required=True)
+    ap.add_argument("--dump-fields", default="",
+                    help="research capture: comma-separated paper cycles, e.g. 11,21,30,31")
+    args = ap.parse_args()
+    D, T = args.D, args.T or 126 * args.D
+    if T % 360:
+        raise SystemExit("T must be a multiple of 360 steps")
+    if os.path.realpath(args.out).startswith(os.path.realpath(os.path.join(os.path.dirname(__file__), "..", ".."))):
+        raise SystemExit("--out must be outside the checkout")
+    cfg, u_max, n = config(D, args.box, T)
+    A, R = p.amplitude(D), 0.5 * D
+    xm = ym = 0.5 * (n - 1)
+    os.makedirs(args.out, exist_ok=True)
+
+    from CelerisLab.body.motion import Translation
+    from CelerisLab.simulation import Simulation
+    with tempfile.NamedTemporaryFile("w", suffix=".json", delete=False) as fh:
+        json.dump(cfg, fh)
+    sim = Simulation(fh.name)
+    try:
+        body = sim.add_body("circle", (xm + A, ym), R,
+                            translation=Translation((-2.0 * A, 0.0, 0.0, 0.0), 1.01 * u_max))
+        sim.initialize()
+        dump = {int(c) for c in args.dump_fields.split(",") if c}
+        if dump:
+            import capture
+            if max(dump) > args.cycles or min(dump) <= p.DISCARD:
+                raise SystemExit("--dump-fields cycles must lie in the scored range of this run")
+            crop = capture.crop_box(xm, ym, D, n, (xm - A - R, xm + A + R, ym - R, ym + R))
+            trend = []
+        steps = int(round((0.25 + args.cycles) * T))
+        force = np.zeros((steps, 2)); diag = []; samples = []
+        for m in range(steps):
+            x0, x1 = p.position(m, T, A), p.position(m + 1, T, A)
+            sim.set_body(body, offset=(max(x1 - A, -2.0 * A), 0.0), vx=x1 - x0)
+            sim.run(1)
+            force[m] = sim.read_force(body)[:2]
+            diag.append(sim.moving_diagnostics()[0])
+            s = m + 1  # state after the step
+            ph = p.bin_phase(s, T)
+            if ph is not None and p.cycle(s, T) > p.DISCARD:
+                fields = sim.get_macroscopic()
+                fluid = (sim.get_flags().reshape(n, n) & 1) != 0
+                ux, uy = (np.asarray(fields[k]).reshape(n, n) for k in ("ux", "uy"))
+                if dump:  # research capture only; the default path is unchanged
+                    rho = np.asarray(fields["rho"]).reshape(n, n)
+                    trend.append(capture.trend_row(s, p.cycle(s, T), ph, rho, ux, uy, fluid, D, n, crop))
+                    if p.cycle(s, T) in dump and p.phase(s, T) == ph:  # first step of the bin
+                        x0c, x1c, y0c, y1c = crop
+                        cy_, cx_ = slice(y0c, y1c + 1), slice(x0c, x1c + 1)
+                        np.savez_compressed(
+                            os.path.join(args.out, f"fields_c{p.cycle(s, T)}_p{int(ph)}.npz"),
+                            s=s, cycle=p.cycle(s, T), phase=ph, crop=np.asarray(crop),
+                            force=force[m], centre=np.asarray((xm + p.position(s, T, A), ym)),
+                            ux=ux[cy_, cx_].astype(np.float32), uy=uy[cy_, cx_].astype(np.float32),
+                            rho=rho[cy_, cx_].astype(np.float32), fluid=fluid[cy_, cx_].astype(np.uint8),
+                            down_ux=capture.downsample(ux, fluid), down_uy=capture.downsample(uy, fluid),
+                            down_rho=capture.downsample(rho, fluid))
+                centre = (xm + p.position(s, T, A), ym)  # analytic centre after the step
+                for xs in p.STATIONS:
+                    for x2 in p.X2:
+                        x, y = xm + xs * D, ym + x2 * D
+                        u, wu, wsum = p.sample(ux, fluid, x, y, centre, R)
+                        v, _, _ = p.sample(uy, fluid, x, y, centre, R)
+                        samples.append((s, p.cycle(s, T), ph, xs, x2,
+                                        math.nan if u is None else u, math.nan if v is None else v,
+                                        wsum, json.dumps(wu)))
+        if dump:
+            np.save(os.path.join(args.out, "trend.npy"), np.asarray(trend, float))
+        np.savez(os.path.join(args.out, "raw.npz"), force=force, diag=np.asarray(diag),
+                 samples=np.asarray([r[:8] for r in samples], float))
+        with open(os.path.join(args.out, "case.json"), "w") as fh:
+            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()
+
+
+if __name__ == "__main__":
+    main()

research/viv_re150/README.md

@@ -0,0 +1,23 @@
+# Research VIV driver — coupling contract (not production)
+
+`run.py` couples a 1-DOF undamped spring–mass (`viv.py`) to the production
+moving-circle API. Everything specific to fluid–structure coupling lives here,
+not in `src/`.
+
+- Per step: known (y_n, v_n) and the last completed force F_last → exact
+  harmonic candidate (y_{n+1}, v_{n+1}) → `set_body(offset=(0, y_{n+1}),
+  vy=y_{n+1} − y_n)` (interval wall velocity, lattice dt = 1) → `run(1)` →
+  commit y, v and F_last only after the step succeeded. One step of explicit
+  force lag (weak coupling); no sub-iteration.
+- Structural RHS = CME + Wen (y), read from `moving_diagnostics()` by the
+  names in `MovingTables.DIAG`; raw CME, the `obs` force and node terms are
+  logged as diagnostics. This is a stage choice, not a validated force law.
+- Production guarantees used: fail-closed target commit (synchronized step,
+  `no_donor == 0`), input rejection before mutation, a failed device step
+  marks the Simulation failed.
+- Not provided, by design: device-resident structure state or batched
+  (multi-step) coupling, strong/sub-iterated coupling (would need state
+  rollback), more than one DOF. These are future work and would be a separate
+  execution path, not an abstraction over this driver.
+- Recorded result and limits: `docs/validation/moving_bodies_stage1.md`;
+  predeclaration: `docs/validation/viv_re150_predeclare.md`.

research/viv_re150/run.py

@@ -0,0 +1,135 @@
+"""One-shot predeclared VIV run (docs/validation/viv_re150_predeclare.md).
+
+Re 150, U* = 5, m/(rho D^2) = 2, zeta = 0, D = 40 on a 75 D x 60 D native
+channel (uniform inlet, NEQ outlet, free-slip y walls), cylinder at
+(30 D, 30 D). Structural RHS = CME + Wen (diagnostics: raw CME, node terms).
+Research driver only: Simulation API, no production change.
+
+    PYTHONPATH=src python research/viv_re150/run.py --out /path/outside/checkout
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import math
+import os
+import tempfile
+
+import numpy as np
+
+import viv
+
+D, U = 40, 0.04
+TEMPLATE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "..", "src",
+                        "CelerisLab", "configs", "config_lbm.json")
+
+
+def config(D=D, U=U):
+    nx, ny = 75 * D, 60 * D
+    with open(TEMPLATE) as fh:
+        cfg = json.load(fh)
+    cfg["grid"].update(lattice_model="D2Q9", nx=nx, ny=ny, nz=1)
+    cfg["physics"].update(data_type="FP32", viscosity=U * D / viv.RE, velocity=U, rho=1.0)
+    cfg["method"].update(collision="MRT", streaming="double_buffer", store_precision="FP32",
+                         ddf_shifting=False, y_wall_bc="free_slip")
+    cfg["method"]["les"]["enabled"] = False
+    cfg["method"]["inlet"]["profile"] = "uniform"
+    return cfg, nx, ny
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--out", required=True)
+    ap.add_argument("--D", type=int, default=D)
+    ap.add_argument("--smoke", action="store_true",
+                    help="plumbing smoke only: exactly --steps steps (<= 64), never scored")
+    ap.add_argument("--steps", type=int, default=0)
+    args = ap.parse_args()
+    if args.smoke != bool(args.steps) or args.steps > 64 or args.steps < 0:
+        raise SystemExit("--smoke requires --steps N with 1 <= N <= 64 (and only with --smoke)")
+    if args.D != D and not args.smoke:
+        raise SystemExit("the physical case is predeclared at D = 40")
+    if os.path.realpath(args.out).startswith(os.path.realpath(os.path.join(os.path.dirname(__file__), "..", ".."))):
+        raise SystemExit("--out must be outside the checkout")
+    os.makedirs(args.out, exist_ok=True)
+    for name in ("report.json", "steps.npy"):  # never overwrite earlier evidence
+        if os.path.exists(os.path.join(args.out, name)):
+            raise SystemExit(f"{args.out} already holds {name}; use a fresh output directory")
+    Dn = args.D
+    cfg, nx, ny = config(Dn)
+    s, cyc = viv.Structure(Dn, U), viv.Cycles(Dn)
+    T_n = 1.0 / s.f_n
+    step_cap, n_seed = int(round(viv.STEP_CAP_TN * T_n)), int(round(viv.SEED_TN * T_n))
+    quiet = int(round(5 * T_n))
+    if args.smoke:
+        step_cap = args.steps
+    centre = (30.0 * Dn, 0.5 * (ny - 1))
+
+    from CelerisLab.body.motion import MovingTables, Translation
+    col = {k: MovingTables.DIAG.index(k) for k in ("cme_y", "wen_y", "cover_jy", "uncover_jy", "no_donor")}
+    from CelerisLab.simulation import Simulation
+    with tempfile.NamedTemporaryFile("w", suffix=".json", delete=False) as fh:
+        json.dump(cfg, fh)
+    sim = Simulation(fh.name)
+    rows, status, seed_step, f_last = [], "running", None, 0.0
+    try:
+        body = sim.add_body("circle", centre, 0.5 * Dn,
+                            translation=Translation((0.0, 0.0, -1.5 * Dn, 1.5 * Dn), 0.5))
+        sim.initialize()
+        for n in range(step_cap):
+            # rows[k] holds the state y_{k+1}; the declared window is y_t, t in [n_seed - 5 T_n, n_seed)
+            if not args.smoke and n == n_seed and \
+                    max(abs(r[1]) for r in rows[n_seed - quiet - 1:n_seed - 1]) < viv.ELIGIBLE * Dn:
+                s.v += s.seed_velocity(Dn)         # after the quiet check, before the update
+                seed_step = n
+                cyc.discard_current()
+                cyc.reset_proof()
+            y1, v1 = s.candidate(f_last)
+            if not (math.isfinite(y1) and math.isfinite(v1)) or abs(y1) > viv.Y_LIMIT * Dn:
+                status = "fail_bound_or_nonfinite"
+                break
+            try:
+                sim.set_body(body, offset=(0.0, y1), vy=y1 - s.y)
+            except ValueError as exc:              # input rejection: stop, no retry
+                status = f"rejected: {exc}"
+                break
+            sim.run(1)                             # device failures raise and mark the Simulation failed
+            d = sim.moving_diagnostics()[0]
+            f_obs = sim.read_force(body)[1]
+            f_rhs = float(d[col["cme_y"]] + d[col["wen_y"]])   # CME + Wen (y)
+            row = (n, y1, v1, f_rhs, float(d[col["cme_y"]]), float(d[col["wen_y"]]), float(f_obs),
+                   float(d[col["cover_jy"]] - d[col["uncover_jy"]]), float(d[col["no_donor"]]))
+            if not viv.finite(row):                # every recorded output, not only the RHS
+                status = "fail_nonfinite_output"
+                break
+            s.y, s.v, f_last = y1, v1, f_rhs       # commit only after a successful step
+            rows.append(row)
+            if args.smoke:
+                continue                           # no settle / score in the plumbing smoke
+            if cyc.update(s.y) == "scored":
+                status = "scored"
+                break
+            if cyc.counted >= viv.CYCLE_CAP:
+                status = "timeout_response_cycles"
+                break
+        else:
+            status = ("smoke_ok" if all(r[8] == 0.0 for r in rows) else "smoke_no_donor") \
+                if args.smoke else "timeout_native_steps"
+    except BaseException as exc:
+        status = f"error: {exc!r}"
+        raise
+    finally:
+        np.save(os.path.join(args.out, "steps.npy"), np.asarray(rows, float))
+        report = dict(status=status, smoke=args.smoke, D=Dn, steps=len(rows), t_U_over_D=len(rows) * U / Dn, T_n=T_n,
+                      seed_step=seed_step, counted_cycles=cyc.counted, cycles=cyc.log,
+                      columns=["n", "y", "v", "F_rhs_cme_wen", "F_cme", "F_wen", "F_obs",
+                               "node_cover_minus_uncover_y", "no_donor"])
+        if status == "scored" and not args.smoke:
+            report["score"] = viv.score(cyc.window)
+        with open(os.path.join(args.out, "report.json"), "w") as fh:
+            json.dump(report, fh, indent=1)
+        sim.close()
+
+
+if __name__ == "__main__":
+    main()

research/viv_re150/viv.py

@@ -0,0 +1,126 @@
+"""Pure logic of the predeclared Re 150 free transverse VIV case (stdlib only).
+
+Contract: docs/validation/viv_re150_predeclare.md. Oscillator update with a
+constant force over one lattice step, response-cycle tracking with fixed y = 0
+crossings, eligibility, 10-cycle blocks, settling/scoring with deterministic
+restart, and the conditional seed.
+"""
+from __future__ import annotations
+
+import math
+
+RE, U_STAR, MASS_NUMBER = 150.0, 5.0, 2.0      # m/(rho D^2) = 2 -> m* = 8/pi
+TARGET_A, BAND = 0.520, 0.10                   # Qin §4.5 maximum amplitude, ±10 %
+ELIGIBLE, BLOCK, LAST5 = 0.01, 10, 5           # in D; cycles; cycles
+WINDOW_TOL, LAST5_TOL = 0.02, 0.01
+CYCLE_CAP, STEP_CAP_TN, SEED_TN, Y_LIMIT = 150, 200, 40, 1.0
+
+
+def finite(values):
+    """True iff every recorded value is finite (fail-closed output check)."""
+    return all(math.isfinite(float(v)) for v in values)
+
+
+class Structure:
+    """Undamped spring-mass, exact harmonic update over dt = 1 with constant force."""
+
+    def __init__(self, D, u):
+        self.m = MASS_NUMBER * D * D           # lattice rho = 1
+        self.f_n = u / (U_STAR * D)
+        self.w = 2.0 * math.pi * self.f_n
+        self.k = self.m * self.w * self.w
+        self.y = self.v = 0.0
+
+    def candidate(self, force):
+        ye = force / self.k
+        c, s = math.cos(self.w), math.sin(self.w)
+        return (ye + (self.y - ye) * c + self.v / self.w * s,
+                -(self.y - ye) * self.w * s + self.v * c)
+
+    def seed_velocity(self, D):
+        return self.w * ELIGIBLE * D           # amplitude ~ .01 D
+
+
+class Cycles:
+    """Upward y = 0 crossings, eligibility, blocks, settle/score with restart."""
+
+    def __init__(self, D):
+        self.D = D
+        self.reset_proof()
+        self.counted = 0
+        self.log = []                          # one dict per completed cycle
+        self._cur = None
+        self._prev = 0.0
+        self._since = 0
+
+    def reset_proof(self):
+        self.amps = []                         # eligible amplitudes since proof start
+        self.blocks = []                       # block means
+        self.settled_at = None                 # block index where R held
+        self.window = None                     # completed scoring cycles (list of dicts)
+
+    def discard_current(self):
+        self._cur, self._since = None, 0
+
+    def rule(self, k):
+        """R(k): block-mean change ≤ 2 % and last-five spread ≤ 1 %."""
+        if k < 1:
+            return False
+        w0, w1 = self.blocks[k - 1], self.blocks[k]
+        last = self.amps[(k + 1) * BLOCK - LAST5:(k + 1) * BLOCK]
+        a5 = sum(last) / LAST5
+        return abs(w1 - w0) / w0 <= WINDOW_TOL and max(abs(a - a5) for a in last) / a5 <= LAST5_TOL
+
+    def update(self, y):
+        """Feed y after a committed step; returns 'scored' when a stable window completes."""
+        out = None
+        crossing = self._prev < 0.0 <= y and self._since >= 2
+        if crossing:
+            if self._cur is not None:
+                out = self._close()
+            self._cur, self._since = dict(ymax=y, ymin=y, ysum=0.0, n=0), 0
+        if self._cur is not None:
+            c = self._cur
+            c["ymax"], c["ymin"] = max(c["ymax"], y), min(c["ymin"], y)
+            c["ysum"] += y
+            c["n"] += 1
+        self._since += 1
+        self._prev = y
+        return out
+
+    def _close(self):
+        c = self._cur
+        a = 0.5 * (c["ymax"] - c["ymin"]) / self.D
+        cyc = dict(ymax=c["ymax"] / self.D, ymin=c["ymin"] / self.D,
+                   offset=c["ysum"] / c["n"] / self.D, amp=a, steps=c["n"], eligible=a >= ELIGIBLE)
+        self.log.append(cyc)
+        if not cyc["eligible"]:
+            return None
+        self.counted += 1
+        self.amps.append(a)
+        if self.settled_at is not None:
+            self.window.append(cyc)
+        if len(self.amps) % BLOCK:
+            return None
+        self.blocks.append(sum(self.amps[-BLOCK:]) / BLOCK)
+        k = len(self.blocks) - 1
+        if self.settled_at is None:
+            if self.rule(k):
+                self.settled_at, self.window = k, []
+            return None
+        if not self.rule(k):                   # scoring block failed: restart from it
+            amps, blocks = self.amps[-BLOCK:], self.blocks[-1:]
+            self.reset_proof()
+            self.amps, self.blocks = amps, blocks
+            return None
+        return "scored" if k == self.settled_at + 2 else None
+
+
+def score(window):
+    """Target metric and reported quantities over the 20 scoring cycles."""
+    a_max = max(max(abs(c["ymax"]), abs(c["ymin"])) for c in window)
+    return dict(A_max=a_max, mean_amp=sum(c["amp"] for c in window) / len(window),
+                ymax=max(c["ymax"] for c in window), ymin=min(c["ymin"] for c in window),
+                offset=sum(c["offset"] for c in window) / len(window),
+                T_resp=sum(c["steps"] for c in window) / len(window),
+                within_band=abs(a_max - TARGET_A) <= BAND * TARGET_A)

src/CelerisLab/body/manager.py

@@ -405,7 +405,9 @@ class ObjectManager:
 
         for obj in objects:
             obj.validate_surface_actuation(self.cfg)
-            if (not obj.is_sensor) and (not obj.is_force_region) and hasattr(obj, 'get_curved_list'):
+            # Moving circles never enter the packed static links (docs/moving_bodies.md, section 3).
+            if (not obj.is_sensor) and (not obj.is_force_region) and obj.motion is None \
+                    and hasattr(obj, 'get_curved_list'):
                 (
                     fluid_idx, dirs, q_vals, body_ids,
                     rx_vals, ry_vals, rz_vals, fallback_vals

src/CelerisLab/body/motion.py

@@ -0,0 +1,259 @@
+# CelerisLab/body/motion.py
+"""Host state of a translating circle (dense double buffer, D2Q9 only).
+
+Contract: docs/moving_bodies.md, sections 4a, 5 and 7. The applied geometry
+(last successfully committed offset) and an optional pending target are two
+separate facts; centres are always ``base + offset``. Nothing here touches
+the device: the caller supplies upload/step/synchronize callables.
+"""
+from __future__ import annotations
+
+import math
+from dataclasses import dataclass
+from typing import Callable, Optional, Tuple
+
+MAX_STEP = 0.5     # Euclidean centre displacement per step (lattice cells)
+BAND_MARGIN = 2    # cells added around the swept circle AABB
+R_MIN = 4.0        # smallest radius covered by the donor enumeration
+
+Vec = Tuple[float, float]
+
+# D2Q9 non-rest directions, paired order of lbm/descriptors.
+_CX = (1, -1, 0, 0, 1, -1, 1, -1)
+_CY = (0, 0, 1, -1, 1, -1, -1, 1)
+
+
+def _vec(value, name: str) -> Vec:
+    x, y = (float(v) for v in value)
+    if not (math.isfinite(x) and math.isfinite(y)):
+        raise ValueError(f"{name} must be finite, got {value!r}")
+    return x, y
+
+
+@dataclass(frozen=True)
+class Translation:
+    """Declared motion envelope: offset box (x_min, x_max, y_min, y_max) and speed bound."""
+    offset_box: Tuple[float, float, float, float]
+    max_speed: float
+
+    def __post_init__(self):
+        box = tuple(float(v) for v in self.offset_box)
+        speed = float(self.max_speed)
+        if len(box) != 4 or not all(math.isfinite(v) for v in box + (speed,)):
+            raise ValueError("offset_box needs 4 finite values and max_speed must be finite")
+        if not (box[0] <= 0.0 <= box[1] and box[2] <= 0.0 <= box[3]):
+            raise ValueError("offset_box must contain the zero offset")
+        if not 0.0 < speed <= MAX_STEP:
+            raise ValueError(f"max_speed must satisfy 0 < max_speed <= {MAX_STEP}")
+        object.__setattr__(self, "offset_box", box)
+        object.__setattr__(self, "max_speed", speed)
+
+
+class MovingCircle:
+    """Applied offset, pending target and the fail-closed commit of one circle."""
+
+    def __init__(self, base, radius: float, translation: Translation,
+                 on_failure: Optional[Callable[[BaseException], None]] = None):
+        self.base = _vec(base, "base")
+        self.radius = float(radius)
+        if not (math.isfinite(self.radius) and self.radius >= R_MIN):
+            raise ValueError(f"moving circle radius must be >= {R_MIN}")
+        if not isinstance(translation, Translation):
+            raise TypeError("translation must be a Translation")
+        self.translation = translation
+        self.applied: Vec = (0.0, 0.0)
+        self.pending: Optional[Tuple[Vec, Vec]] = None
+        self.failed = False
+        self._on_failure = on_failure  # owner lifecycle hook (Simulation marks itself failed)
+
+    def centre(self, offset: Vec) -> Vec:
+        return self.base[0] + offset[0], self.base[1] + offset[1]
+
+    def check_target(self, offset, velocity) -> Tuple[Vec, Vec]:
+        """Validate a target against ``applied``; returns it, mutates nothing."""
+        self._require_usable()
+        offset, velocity = _vec(offset, "offset"), _vec(velocity, "velocity")
+        x0, x1, y0, y1 = self.translation.offset_box
+        if not (x0 <= offset[0] <= x1 and y0 <= offset[1] <= y1):
+            raise ValueError(f"offset {offset} outside declared box {self.translation.offset_box}")
+        step = math.hypot(offset[0] - self.applied[0], offset[1] - self.applied[1])
+        if step > MAX_STEP:
+            raise ValueError(f"per-step displacement {step} exceeds {MAX_STEP}")
+        if math.hypot(*velocity) > self.translation.max_speed:
+            raise ValueError(f"velocity {velocity} exceeds max_speed {self.translation.max_speed}")
+        if offset == self.applied and velocity != (0.0, 0.0):
+            raise ValueError("a hold target (offset == applied) needs zero translational velocity")
+        return offset, velocity
+
+    def set_target(self, offset, velocity) -> None:
+        """Replace the pending target (last wins); invalid input keeps the old one."""
+        self.pending = self.check_target(offset, velocity)
+
+    def record(self) -> Tuple[Vec, Vec, Vec]:
+        """Motion record (c_old, c_new, u) for the next single moving step."""
+        self._require_usable()
+        if self.pending is not None:
+            offset, velocity = self.pending
+        else:
+            offset, velocity = self.applied, (0.0, 0.0)
+        return self.centre(self.applied), self.centre(offset), velocity
+
+    def advance(self, upload: Callable, step: Callable, synchronize: Callable) -> None:
+        """Upload the record, run one step and commit only after a successful sync.
+
+        Any exception after the upload is attempted leaves device geometry
+        unknown: the circle is marked failed, never reports applied state again,
+        and the owner's ``on_failure`` hook is called.
+        """
+        record = self.record()
+        try:
+            upload(record)
+            step()
+            synchronize()
+        except BaseException as exc:
+            self.fail(exc)
+            raise
+        self.commit()
+
+    def commit(self) -> None:
+        """Applied := pending offset (caller has synchronized a successful step)."""
+        if self.pending is not None:
+            self.applied = self.pending[0]
+            self.pending = None
+
+    def fail(self, exc: BaseException) -> None:
+        self.failed = True
+        if self._on_failure is not None:
+            self._on_failure(exc)
+
+    def band(self) -> Tuple[int, int, int, int]:
+        """Inclusive cell AABB (x0, x1, y0, y1) swept over the whole offset box."""
+        x0, x1, y0, y1 = self.translation.offset_box
+        r, m = self.radius, BAND_MARGIN
+        return (math.floor(self.base[0] + x0 - r) - m, math.ceil(self.base[0] + x1 + r) + m,
+                math.floor(self.base[1] + y0 - r) - m, math.ceil(self.base[1] + y1 + r) + m)
+
+    def _require_usable(self) -> None:
+        if self.failed:
+            raise RuntimeError("moving circle state is unknown after a failed step")
+
+
+def _inside(x: int, y: int, c: Vec, r: float) -> bool:
+    return (x - c[0]) ** 2 + (y - c[1]) ** 2 < r * r
+
+
+def empty_donor_cells(c_old: Vec, c_new: Vec, radius: float):
+    """Fresh cells (inside c_old, outside c_new) whose donor set V(x) is empty."""
+    r = radius
+    xs = range(math.floor(min(c_old[0], c_new[0]) - r) - 1, math.ceil(max(c_old[0], c_new[0]) + r) + 2)
+    ys = range(math.floor(min(c_old[1], c_new[1]) - r) - 1, math.ceil(max(c_old[1], c_new[1]) + r) + 2)
+    empty = []
+    for x in xs:
+        for y in ys:
+            if not _inside(x, y, c_old, r) or _inside(x, y, c_new, r):
+                continue
+            if not any(not _inside(x + cx, y + cy, c_old, r) and not _inside(x + cx, y + cy, c_new, r)
+                       for cx, cy in zip(_CX, _CY)):
+                empty.append((x, y))
+    return empty
+
+
+def enumerate_donor_coverage(radius: float, positions: int = 8, directions: int = 16) -> int:
+    """Count empty-donor fresh cells over sub-cell centres and moves of MAX_STEP.
+
+    Evidence for the declared bounds (radius >= R_MIN, |dc|_2 <= MAX_STEP),
+    not a proof; the device keeps the ``no_donor`` counter.
+    """
+    count = 0
+    for i in range(positions):
+        for j in range(positions):
+            c_old = (i / positions, j / positions)
+            for k in range(directions):
+                a = 2.0 * math.pi * k / directions
+                c_new = (c_old[0] + MAX_STEP * math.cos(a), c_old[1] + MAX_STEP * math.sin(a))
+                count += len(empty_donor_cells(c_old, c_new, radius))
+    return count
+
+
+class MovingTables:
+    """Device tables of the translating circles for ``MovingCircleCells``/``Links``.
+
+    Band table (x0, y0, width, height, first_slot, body_id), immutable per run;
+    FP64 motion records (cx_old, cy_old, cx_new, cy_new, r, ux, uy), immutable
+    during a step; separate per-body diagnostics (see DIAG), never part of obs.
+    """
+    BAND_INTS, GEOM_DOUBLES = 6, 7
+    DIAG = ("cme_x", "cme_y", "wen_x", "wen_y", "link_dm", "n_links",
+            "cover_jx", "cover_jy", "cover_mass", "uncover_jx", "uncover_jy", "uncover_mass",
+            "eq_only", "no_donor", "crossings")
+    DIAG_FLOATS = len(DIAG)
+
+    def __init__(self, band, geom):
+        import numpy as np
+        import pycuda.driver as cuda
+        self.n_bodies = len(geom) // self.GEOM_DOUBLES
+        self.n_slots = int(band[-2] + band[-4] * band[-3] * 8)
+        self.n_cells = self.n_slots // 8
+        self.geom = list(geom)  # host copy of the uploaded records
+        self.band_gpu = cuda.to_device(np.asarray(band, np.int32))
+        self.geom_gpu = cuda.to_device(np.asarray(geom, np.float64))
+        # Owned page-locked staging for async record uploads (allocated once).
+        self._geom_pinned = cuda.pagelocked_empty(len(geom), np.float64)
+        self.diag_gpu = cuda.to_device(np.zeros(self.n_bodies * self.DIAG_FLOATS, np.float32))
+        self.slot_debug_gpu = None  # optional (q, fallback, rx, ry) per slot for parity tests
+
+    @classmethod
+    def upload(cls, circles):
+        """``circles``: [(MovingCircle, body_id)] in body order."""
+        return cls(*cls.layout(circles))
+
+    @staticmethod
+    def layout(circles):
+        """Host band and geometry tables (no device work)."""
+        band, geom, first = [], [], 0
+        for motion, body_id in circles:
+            x0, x1, y0, y1 = motion.band()
+            width, height = x1 - x0 + 1, y1 - y0 + 1
+            band += [x0, y0, width, height, first, int(body_id)]
+            first += width * height * 8
+            geom += MovingTables.record(motion)
+        return band, geom
+
+    @staticmethod
+    def record(motion):
+        """FP64 motion record of one circle for its next step (hold if nothing pending)."""
+        c_old, c_new, u = motion.record()
+        return [*c_old, *c_new, motion.radius, *u]
+
+    def upload_records(self, circles, stream) -> bool:
+        """Enqueue the records when they differ from the device copy; True if advancing.
+
+        The pinned staging buffer is reused: callers synchronize ``stream`` after every
+        upload before the next one (``Simulation._run_moving``), so no copy is in flight
+        when it is rewritten. ``geom`` is the enqueued state; after a failed copy the
+        owner is failed and the cache is never trusted again.
+        """
+        import pycuda.driver as cuda
+        geom = [v for motion, _ in circles for v in self.record(motion)]
+        if geom != self.geom:
+            self._geom_pinned[:] = geom
+            cuda.memcpy_htod_async(self.geom_gpu, self._geom_pinned, stream)
+            self.geom = geom
+        g = self.GEOM_DOUBLES
+        return any(geom[i:i + 2] != geom[i + 2:i + 4] for i in range(0, len(geom), g))
+
+    def enable_slot_debug(self):
+        import numpy as np
+        import pycuda.driver as cuda
+        self.slot_debug_gpu = cuda.to_device(np.zeros(self.n_slots * 4, np.float32))
+
+    def zero_diagnostics(self, stream):
+        import pycuda.driver as cuda
+        cuda.memset_d32_async(self.diag_gpu, 0, self.n_bodies * self.DIAG_FLOATS, stream)
+
+    def download_diagnostics(self):
+        import numpy as np
+        import pycuda.driver as cuda
+        out = np.empty((self.n_bodies, self.DIAG_FLOATS), np.float32)
+        cuda.memcpy_dtoh(out, self.diag_gpu)
+        return out

src/CelerisLab/body/objects.py

@@ -140,6 +140,7 @@ class SimObject:
             x=float(c[0]), y=float(c[1]), z=z0,
         )
         self.control = ObjectControl()
+        self.motion = None  # MovingCircle for a translating circle (body/motion.py)
 
     @property
     def surface_actuation(self):

src/CelerisLab/configs/CONFIG.md

@@ -86,6 +86,20 @@ step/one_step_*.cu         → kernel 编排
 - 转速 `omega` 属于运行时状态，可在步进期间更新；该更新不改变 `N_OBJS` 或 `OBS_*` 内存布局，因此**不需要**因 `omega` 变化触发重新编译。
 - 力矩观测从 `obs` 的 torque segment 读取；force / torque / sensor 段统一由 `config_obs.h` 宏描述。
 
+### 外边界能力（Outer boundaries, dense `Simulation`）
+
+The dense path supports one channel package, not four independently
+selectable sides:
+- left x = 0: velocity inlet (`method.inlet.scheme`, `profile`, `physics.velocity`);
+- right x = nx−1: outlet (`method.outlet.mode`; `neq_extrap` holds rho = 1 with
+  a `max(u, 0)` backflow clamp when `backflow_clamp` is set);
+- bottom and top: one shared `y_wall_bc` (`bounce_back` halfway or
+  `free_slip`); corners are walls.
+`y_wall_bc = "on_site_velocity"` switches to x-periodic with on-site y planes
+and requires an object-free domain. There is no x/y-periodic or symmetry
+option for domains with bodies; adding outer BC types is a separate design
+question, not covered by these keys.
+
 ### 稳定性默认窗口（Stability defaults）
 
 - 默认 `method.omega_guard = {min: 0.01, max: 1.99}`，用于约束碰撞频率与 LES 有效粘度路径。

src/CelerisLab/lbm/kernels/step/moving_circle.cu

@@ -0,0 +1,183 @@
+// Translating circles (docs/moving_bodies.md): M1 MovingCircleCells reclassifies
+// band cells and refills uncovered ones; M2 MovingCircleLinks applies the cut links.
+// Geometry comes from an immutable FP64 record per body
+// {cx_old, cy_old, cx_new, cy_new, r, ux, uy}; the M2 operation order mirrors
+// CircleGeometry.build_cut_links / find_circle_intersection with explicit _rn
+// operations (bit parity with the host builder is a test target, not a claim).
+// Moving circles are never in the packed static links, so this kernel is the
+// only writer of their solid slots.
+#ifndef CELERIS_MOVING_CIRCLE_CU
+#define CELERIS_MOVING_CIRCLE_CU
+
+#if DIM == 2
+constexpr int MOVING_BAND_INTS = 6;   // x0, y0, width, height, first_slot, body_id
+constexpr int MOVING_GEOM_DOUBLES = 7;
+// cme_x, cme_y, wen_x, wen_y, link_dm, n_links, cover_jx, cover_jy, cover_mass,
+// uncover_jx, uncover_jy, uncover_mass, eq_only, no_donor, crossings
+constexpr int MOVING_DIAG_FLOATS = 15;
+
+__device__ __forceinline__ double mc_sq(double v) { return __dmul_rn(v, v); }
+
+__device__ __forceinline__ bool mc_inside(int x, int y, double cx, double cy, double r)
+{
+    return __dadd_rn(mc_sq(__dsub_rn((double)x, cx)), mc_sq(__dsub_rn((double)y, cy))) < mc_sq(r);
+}
+
+// Smallest root t in [0, 1] of |p + t c - centre| = r (find_circle_intersection order).
+__device__ __forceinline__ bool mc_hit(int x, int y, int ex, int ey,
+                                       double cx, double cy, double r, double& t)
+{
+    const double dx = (double)ex, dy = (double)ey;
+    const double px = __dsub_rn((double)x, cx), py = __dsub_rn((double)y, cy);
+    const double a = __dadd_rn(mc_sq(dx), mc_sq(dy));
+    const double b = __dmul_rn(2.0, __dadd_rn(__dmul_rn(dx, px), __dmul_rn(dy, py)));
+    const double c = __dsub_rn(__dadd_rn(mc_sq(px), mc_sq(py)), mc_sq(r));
+    const double det = __dsub_rn(mc_sq(b), __dmul_rn(__dmul_rn(4.0, a), c));
+    if (det < 0.0) return false;
+    const double s = __dsqrt_rn(det), a2 = __dmul_rn(2.0, a);
+    const double t1 = __ddiv_rn(__dsub_rn(-b, s), a2);
+    const double t2 = __ddiv_rn(__dadd_rn(-b, s), a2);
+    if (0.0 <= t1 && t1 <= 1.0) { t = t1; return true; }
+    if (0.0 <= t2 && t2 <= 1.0) { t = t2; return true; }
+    return false;
+}
+
+__global__ void MovingCircleLinks(
+    fpxx* fi, const uint16_t* flag,
+    const int* band, const double* geom,
+    unsigned int n_bodies, unsigned int n_slots,
+    const float* action, float* obs, float* diag, float* slot_debug)
+{
+    const unsigned int tid = threadIdx.x + blockIdx.x * blockDim.x;
+    if (tid >= n_slots) return;
+    unsigned int m = 0;
+    while (m + 1 < n_bodies && tid >= (unsigned int)band[(m + 1) * MOVING_BAND_INTS + 4]) ++m;
+    const int* b = band + m * MOVING_BAND_INTS;
+    const unsigned int local = tid - (unsigned int)b[4];
+    const unsigned int dir = local % 8u + 1u;
+    const int x = b[0] + (int)((local / 8u) % (unsigned int)b[2]);
+    const int y = b[1] + (int)((local / 8u) / (unsigned int)b[2]);
+    const double* g = geom + MOVING_GEOM_DOUBLES * m;
+    const double cx = g[2], cy = g[3], r = g[4];
+    const int ex = d_cx[dir], ey = d_cy[dir];
+    float* debug = slot_debug == nullptr ? nullptr : slot_debug + 4 * tid;
+    if (debug != nullptr) debug[0] = -1.0f;
+
+    double t;
+    if (mc_inside(x, y, cx, cy, r) || !mc_inside(x + ex, y + ey, cx, cy, r)
+            || !mc_hit(x, y, ex, ey, cx, cy, r, t))
+        return;
+    const double hx = __dadd_rn((double)x, __dmul_rn(t, (double)ex));
+    const double hy = __dadd_rn((double)y, __dmul_rn(t, (double)ey));
+    const double hdx = __dsub_rn(hx, (double)x), hdy = __dsub_rn(hy, (double)y);
+    const double norm = __dsqrt_rn((double)(ex * ex + ey * ey));
+    double qd = __ddiv_rn(__dsqrt_rn(__dadd_rn(mc_sq(hdx), mc_sq(hdy))), norm);
+    qd = fmax(0.01, fmin(qd, 1.0));
+    const float q = (float)qd;
+    const float rx = (float)__dsub_rn(hx, cx), ry = (float)__dsub_rn(hy, cy);
+
+    // Same two-stage order as build_cut_links + pack_cut_links_to_soa: the fallback
+    // class is chosen from the clamped FP64 q (q < 1/2 needs a fluid donor at x - c);
+    // only then are q, rx, ry rounded to FP32 for the BFL branch and spin velocity.
+    unsigned char fallback = CURVED_FALLBACK_BOUZIDI;
+    if (qd < 0.5) {
+        const int xd = x - ex, yd = y - ey;
+        if (xd < 0 || xd >= (int)NX || yd < 0 || yd >= (int)NY || mc_inside(xd, yd, cx, cy, r)
+                || (flag[linear_index((unsigned int)xd, (unsigned int)yd)] & FLAG_FLUID) == 0)
+            fallback = CURVED_FALLBACK_HALFWAY;
+    }
+    if (debug != nullptr) { debug[0] = q; debug[1] = (float)fallback; debug[2] = rx; debug[3] = ry; }
+
+    const int bid = b[5];
+    const float omega = action_omega(action, bid);
+    const float Uw = (float)g[5] - omega * ry, Vw = (float)g[6] + omega * rx;  // u + omega x r
+    float exchange[3], dm;
+    apply_bouzidi_link(dir, q, linear_index((unsigned int)x, (unsigned int)y), fi,
+                       Uw, Vw, rx, ry, fallback, obs, bid, exchange, &dm);
+    if (diag != nullptr) {
+        float* d = diag + m * MOVING_DIAG_FLOATS;
+        atomicAdd(&d[0], exchange[0]);
+        atomicAdd(&d[1], exchange[1]);
+        atomicAdd(&d[2], Uw * dm);   // Wen 2014 correction -u_w (f_t - f_r)
+        atomicAdd(&d[3], Vw * dm);
+        atomicAdd(&d[4], dm);
+        atomicAdd(&d[5], 1.0f);
+    }
+}
+// M1: one thread per band cell, launched only on steps with c_old != c_new.
+// Membership comes from the immutable old/new predicates, never from flags, so
+// classification, refill and the flag write of one cell cannot race with another.
+// ddf holds post-collision G^{n-1}; refilled cells get all nine slots at that level.
+__global__ void MovingCircleCells(
+    fpxx* fi, uint16_t* flag, const int* band, const double* geom,
+    unsigned int n_bodies, unsigned int n_cells, const float* action, float* diag)
+{
+    const unsigned int tid = threadIdx.x + blockIdx.x * blockDim.x;
+    if (tid >= n_cells) return;
+    unsigned int m = 0;
+    while (m + 1 < n_bodies && tid >= (unsigned int)band[(m + 1) * MOVING_BAND_INTS + 4] / 8u) ++m;
+    const int* b = band + m * MOVING_BAND_INTS;
+    const unsigned int local = tid - (unsigned int)b[4] / 8u;
+    const int x = b[0] + (int)(local % (unsigned int)b[2]);
+    const int y = b[1] + (int)(local / (unsigned int)b[2]);
+    const double* g = geom + MOVING_GEOM_DOUBLES * m;
+    const bool in_old = mc_inside(x, y, g[0], g[1], g[4]);
+    const bool in_new = mc_inside(x, y, g[2], g[3], g[4]);
+    if (in_old == in_new) return;
+    const unsigned long k = linear_index((unsigned int)x, (unsigned int)y);
+    float* d = diag + m * MOVING_DIAG_FLOATS;
+    float rho = 0.0f, jx = 0.0f, jy = 0.0f;
+    if (in_new) {  // covered: its fluid content leaves the active set
+        for (unsigned int i = 0; i < NQ; ++i) {
+            const float f = load_ddf(fi, index_f(k, i));
+            rho += f; jx += (float)d_cx[i] * f; jy += (float)d_cy[i] * f;
+        }
+        flag[k] = FLAG_SOLID | FLAG_OBSTACLE | FLAG_BC_CURVED;
+        atomicAdd(&d[6], jx); atomicAdd(&d[7], jy); atomicAdd(&d[8], rho);
+        atomicAdd(&d[14], 1.0f);
+        return;
+    }
+    // Uncovered: donors are fluid in BOTH geometries; NEQ from the neighbour with the
+    // largest unnormalized c.n > 0 (first direction wins ties), n from c_new.
+    const float nx = (float)__dsub_rn((double)x, g[2]), ny = (float)__dsub_rn((double)y, g[3]);
+    float rho_sum = 0.0f, best_dot = 0.0f;
+    int n_valid = 0, best = -1;
+    for (unsigned int i = 1; i < NQ; ++i) {
+        const int xn = x + d_cx[i], yn = y + d_cy[i];
+        if (mc_inside(xn, yn, g[0], g[1], g[4]) || mc_inside(xn, yn, g[2], g[3], g[4])) continue;
+        const unsigned long kn = linear_index((unsigned int)xn, (unsigned int)yn);
+        for (unsigned int q = 0; q < NQ; ++q) rho_sum += load_ddf(fi, index_f(kn, q));
+        ++n_valid;
+        const float dot = (float)d_cx[i] * nx + (float)d_cy[i] * ny;
+        if (dot > best_dot) { best_dot = dot; best = (int)i; }
+    }
+    const float omega = action_omega(action, b[5]);
+    const float uwx = (float)g[5] - omega * ny, uwy = (float)g[6] + omega * nx;  // at the cell
+    float feq[NQ], neq[NQ];
+    compute_feq(n_valid > 0 ? rho_sum / (float)n_valid : (float)RHO, uwx, uwy, feq);
+    for (unsigned int i = 0; i < NQ; ++i) neq[i] = 0.0f;
+    if (best >= 0) {
+        const unsigned long kd = linear_index((unsigned int)(x + d_cx[best]), (unsigned int)(y + d_cy[best]));
+        float gd[NQ], rd = 0.0f, mx = 0.0f, my = 0.0f, fd[NQ];
+        for (unsigned int i = 0; i < NQ; ++i) {
+            gd[i] = load_ddf(fi, index_f(kd, i));
+            rd += gd[i]; mx += (float)d_cx[i] * gd[i]; my += (float)d_cy[i] * gd[i];
+        }
+        compute_feq(rd, mx / rd, my / rd, fd);
+        for (unsigned int i = 0; i < NQ; ++i) neq[i] = gd[i] - fd[i];
+    } else {
+        atomicAdd(&d[12], 1.0f);
+    }
+    if (n_valid == 0) atomicAdd(&d[13], 1.0f);  // hard failure, checked before commit
+    for (unsigned int i = 0; i < NQ; ++i) {
+        const float f = feq[i] + neq[i];
+        store_ddf(fi, index_f(k, i), f);
+        rho += f; jx += (float)d_cx[i] * f; jy += (float)d_cy[i] * f;
+    }
+    flag[k] = FLAG_FLUID;
+    atomicAdd(&d[9], jx); atomicAdd(&d[10], jy); atomicAdd(&d[11], rho);
+    atomicAdd(&d[14], 1.0f);
+}
+#endif  // DIM == 2
+
+#endif  // CELERIS_MOVING_CIRCLE_CU

src/CelerisLab/lbm/kernels/uniform.cu

@@ -71,6 +71,7 @@ extern "C"
 #include "step/one_step_double.cu"
 #include "step/one_step_esopull.cu"
 #include "step/aux_kernels.cu"
+#include "step/moving_circle.cu"
 #include "step/esopull_macro.cu"
 #include "step/esopull_sync.cu"
 

src/CelerisLab/lbm/stepper.py

@@ -20,6 +20,10 @@ class LBMStepper:
         self.cfg = cfg
 
         self._esopull = (cfg.streaming == "esopull")
+        # Set by the owner when a step would be wrong (translating circles
+        # excluded from the packed links before the moving kernels exist).
+        self.blocked: str | None = None
+        self.moving = None  # MovingTables attached by the owner (translating circles)
 
         if self._esopull:
             self.step_fn = module.get_function("EsoPullStep")
@@ -35,6 +39,8 @@ class LBMStepper:
         self.apply_esopull_curved_fn = module.get_function("ApplyEsoPullCurvedKernel")
         self.sensor_fn = module.get_function("SensorKernel")
         self.force_region_fn = module.get_function("ForceRegionKernel")
+        self.moving_fn = None if self._esopull else module.get_function("MovingCircleLinks")
+        self.moving_cells_fn = None if self._esopull else module.get_function("MovingCircleCells")
 
         tpb = cfg.threads_per_block
         self.block = (tpb, 1, 1)
@@ -70,6 +76,13 @@ class LBMStepper:
         stream: cuda.Stream | None = None,
     ):
         """Advance *n* time steps."""
+        if n > 0 and self.blocked is not None:
+            raise RuntimeError(self.blocked)
+        self._step(n, action_gpu=action_gpu, obs_gpu=obs_gpu, stream=stream)
+
+    def _step(self, n, *, action_gpu, obs_gpu, stream=None, advance=False):
+        """Unguarded steps; ``advance`` runs one step that moves translating circles."""
+        assert not advance or n == 1
         f = self.field
         launch_kw = {}
         if stream is not None:
@@ -81,6 +94,8 @@ class LBMStepper:
                     f.ddf_gpu, self.boundary_values_gpu, np.uint64(self._step_count),
                     block=self.block, grid=self.boundary_grid, **launch_kw,
                 )
+            if self.moving is not None:
+                self._launch_moving(action_gpu, obs_gpu, advance, **launch_kw)
             self._launch_curved(action_gpu, obs_gpu, **launch_kw)
 
             if self._esopull:
@@ -106,6 +121,21 @@ class LBMStepper:
             # Any completed GPU step invalidates host DDF mirror.
             f.invalidate_host_ddf_cache()
 
+    def _launch_moving(self, action_gpu, obs_gpu, advance, **launch_kw):
+        m, tpb = self.moving, self.cfg.threads_per_block
+        if advance:  # M1 completes before M2 on the same stream
+            self.moving_cells_fn(
+                self.field.ddf_gpu, self.field.flag_gpu, m.band_gpu, m.geom_gpu,
+                np.uint32(m.n_bodies), np.uint32(m.n_cells), action_gpu, m.diag_gpu,
+                block=(tpb, 1, 1), grid=((m.n_cells + tpb - 1) // tpb, 1, 1), **launch_kw,
+            )
+        self.moving_fn(
+            self.field.ddf_gpu, self.field.flag_gpu, m.band_gpu, m.geom_gpu,
+            np.uint32(m.n_bodies), np.uint32(m.n_slots), action_gpu, obs_gpu,
+            m.diag_gpu, m.slot_debug_gpu if m.slot_debug_gpu is not None else np.uintp(0),
+            block=(tpb, 1, 1), grid=((m.n_slots + tpb - 1) // tpb, 1, 1), **launch_kw,
+        )
+
     def _launch_curved(self, action_gpu, obs_gpu, **launch_kw):
         f = self.field
         if f.n_curved == 0:

src/CelerisLab/simulation.py

@@ -26,6 +26,13 @@ import pycuda.driver as cuda
 from .config import LBMConfig, BodyConfig, load_lbm_config, load_body_config
 from .cuda.context import CudaContext, context_bound
 from .cuda import compiler
+from .lbm.descriptors import FLUID
+
+# Translating circles step only through their moving tables (attached at initialize).
+PENDING_BLOCKED = "a pending translation target is advanced only by Simulation.run(1)"
+MOVING_BLOCKED = ("translating circles need the moving kernels and their tables (attached "
+                  "at initialize); "
+                  "positive-step runs are rejected")
 from .lbm.field import LBMField
 from .lbm.stepper import LBMStepper
 from .body.objects import SimObject
@@ -97,7 +104,8 @@ class Simulation:
 
     # -- Object management ---------------------------------------------------
     def add_body(self, type: str = "circle", center=None,
-                 radius: float = 0.0, *, surface_actuation=None, **kwargs) -> int:
+                 radius: float = 0.0, *, surface_actuation=None, translation=None,
+                 **kwargs) -> int:
         """Add a simulation body. Returns body_id.
 
         Before ``initialize()`` the object is added to the formal registry
@@ -113,6 +121,10 @@ class Simulation:
                 angle, half_width (radians), normal_velocity (positive outward).
                 D2Q9/FP32/unshifted/DB only; set before initialization or stage
                 a new body. No runtime motion or amplitude setter.
+            translation: ``body.motion.Translation`` declaring a translating
+                circle (before initialize only; docs/moving_bodies.md).
+                Positive-step runs are rejected until ``initialize()`` has
+                attached its moving tables.
             **kwargs: passed to the geometry constructor.
 
         Returns:
@@ -123,6 +135,10 @@ class Simulation:
         type_lower = str(type).strip().lower()
         if surface_actuation is not None and type_lower != "circle":
             raise ValueError("Surface actuation is only supported on circles")
+        if translation is not None and (type_lower != "circle" or surface_actuation is not None
+                                        or self._initialized):
+            raise ValueError("translation needs a circle without surface actuation, "
+                             "added before initialize()")
 
         if type_lower == "circle":
             from .body.geometry.circle import CircleGeometry
@@ -131,6 +147,11 @@ class Simulation:
             obj = SimObject(obj_id=-1, geometry=geom,
                             center=center, radius=radius,
                             is_sensor=False, surface_actuation=surface_actuation)
+            if translation is not None:
+                from .body.motion import MovingCircle
+                obj.motion = MovingCircle((cx, cy), radius, translation,
+                                          on_failure=self._fail_moving)
+                self.stepper.blocked = MOVING_BLOCKED
         elif type_lower == "sensor":
             from .body.geometry.circle import CircleGeometry
             cx, cy = float(center[0]), float(center[1])
@@ -190,6 +211,78 @@ class Simulation:
                 raise
         self.bodies.jets[index] = jet  # later geometry syncs keep the new amplitude
 
+    def _fail_moving(self, exc: BaseException) -> None:
+        # Device geometry is unknown after a failed moving step: same lifecycle as Jets.
+        self._failed = f"moving circle step failed: {exc!r}"
+        self.stepper.blocked = self._failed  # direct stepper calls are refused as well
+
+    def _attach_moving(self) -> None:
+        # Direct stepper calls stay blocked until the moving tables exist.
+        tables = getattr(self, "_moving_tables", None)
+        self.stepper.moving = tables
+        moving = self._moving_bodies()
+        if moving and tables is None:
+            self.stepper.blocked = MOVING_BLOCKED
+        elif any(obj.motion.pending is not None for obj in moving):
+            self.stepper.blocked = PENDING_BLOCKED  # direct steps never consume a target
+        else:
+            self.stepper.blocked = None
+
+    def _build_moving_tables(self):
+        moving = self._moving_bodies()
+        if not moving:
+            return None
+        from .body.motion import MovingTables
+        return MovingTables.upload([(obj.motion, obj.obj_id) for obj in moving])
+
+    @context_bound
+    def moving_diagnostics(self) -> np.ndarray:
+        """Per translating circle (in body order), columns ``MovingTables.DIAG``,
+        accumulated since obs were last zeroed (diagnostics only, not a force RHS)."""
+        self._require_usable()
+        tables = self.stepper.moving
+        if tables is None:
+            return np.zeros((0, 6), np.float32)
+        self.stream.synchronize()
+        return tables.download_diagnostics()
+
+    def _moving_bodies(self):
+        return [obj for obj in self.bodies.objects if obj.motion is not None]
+
+    def _reject_moving_bodies(self, operation: str) -> None:
+        if self._moving_bodies():
+            raise ValueError(f"{operation} is not supported with translating circles")
+
+    def _validate_moving_bodies(self) -> None:
+        """Reject unsupported modes and swept-band placement before any mutation."""
+        moving = self._moving_bodies()
+        if not moving:
+            return
+        cfg = self.lbm_cfg
+        if (not cfg.is_d2q9 or cfg.streaming != "double_buffer" or cfg.ddf_shifting
+                or cfg.store_precision != "FP32"):
+            raise ValueError("translating circles need D2Q9/FP32/unshifted/double_buffer")
+        if self.bodies.jets:
+            raise ValueError("Jets are not supported together with translating circles")
+        nx, ny = self.field.nx, self.field.ny
+        base = self.field.build_channel_flags().reshape(ny, nx)
+        for obj in moving:
+            x0, x1, y0, y1 = obj.motion.band()
+            if x0 < 1 or y0 < 1 or x1 > nx - 2 or y1 > ny - 2:
+                raise ValueError(f"swept band {(x0, x1, y0, y1)} touches the domain edge")
+            if not np.all((base[y0:y1 + 1, x0:x1 + 1] & FLUID) != 0):
+                raise ValueError(f"swept band {(x0, x1, y0, y1)} contains non-fluid base cells")
+            for other in self.bodies.objects:
+                if other is obj:
+                    continue
+                (cx, cy), r = other.center[:2], float(other.radius)
+                if other.motion is not None:
+                    ox0, ox1, oy0, oy1 = other.motion.band()
+                else:
+                    ox0, ox1, oy0, oy1 = cx - r - 2, cx + r + 2, cy - r - 2, cy + r + 2
+                if ox0 <= x1 and x0 <= ox1 and oy0 <= y1 and y0 <= oy1:
+                    raise ValueError(f"swept band {(x0, x1, y0, y1)} overlaps body {other.obj_id}")
+
     def _require_usable(self):
         failed = getattr(self, "_failed", None)
         if failed is not None:
@@ -260,7 +353,7 @@ class Simulation:
 
     # -- Runtime control -----------------------------------------------------
     def set_body(self, id: int, omega: float = None,
-                 vx: float = None, vy: float = None) -> None:
+                 vx: float = None, vy: float = None, offset=None) -> None:
         """Set runtime body state (host action array only, no H2D).
 
         The GPU action buffer is updated at the next ``run()`` call.
@@ -268,10 +361,26 @@ class Simulation:
         Args:
             id: body_id from add_body().
             omega: rotation speed (lattice units).  ``None`` = no change.
-            vx: translation velocity x (future).  ``None`` = no change.
-            vy: translation velocity y (future).  ``None`` = no change.
+            vx: translation velocity x. For a translating circle: the
+                interval wall velocity of the target, only together with
+                ``offset``; otherwise stored in the body state (not applied
+                to stationary walls).  ``None`` = no change.
+            vy: translation velocity y; same rules as ``vx``.
+            offset: target centre offset of a translating circle; with vx/vy
+                (default 0) it replaces the pending target after validation
+                against the applied offset (docs/moving_bodies.md, 4a). Only
+                ``run(1)`` advances it; direct stepper calls are blocked meanwhile.
         """
         obj = self.bodies.get(id)
+        motion = obj.motion
+        if motion is not None:
+            if offset is None and (vx is not None or vy is not None):
+                raise ValueError("a translating circle takes vx/vy only with an offset")
+            target = None if offset is None else motion.check_target(
+                offset, (0.0 if vx is None else vx, 0.0 if vy is None else vy))
+            vx = vy = None  # the motion target, not ObjectState, owns translation
+        elif offset is not None:
+            raise ValueError(f"body {id} was not declared with a translation")
         proposed = dict(vars(obj.state))
         proposed.update({k: float(v) for k, v in (("omega", omega), ("vx", vx), ("vy", vy))
                          if v is not None})
@@ -287,6 +396,9 @@ class Simulation:
         if vy is not None:
             obj.state.vy = float(vy)
             changed = True
+        if motion is not None and target is not None:
+            motion.pending = target
+            self._attach_moving()
         if changed:
             self.bodies._refresh_action_from_objects()
 
@@ -443,6 +555,7 @@ class Simulation:
             self.field, self._module, self.lbm_cfg,
         )
         self.stepper._step_count = _prev_step_count
+        self._attach_moving()
 
         self._assert_object_count_contract(expected_count=expected_n_objects)
 
@@ -468,6 +581,8 @@ class Simulation:
         # Validate the complete geometry before flags, populations or modules
         # change. Compact-list construction publishes no outputs on failure.
         next_flags = self.bodies.build_flags(self.field.build_channel_flags())
+        self._validate_moving_bodies()
+        self._attach_moving()
         if self.bodies.jets and self.bodies.count == 0:
             raise ValueError("Jets need bodies with cut links")
         self.bodies.build_compact_lists_for(self.bodies.objects, next_flags)
@@ -484,6 +599,8 @@ class Simulation:
             self.bodies.sync_to_gpu(self.field, rebuild_flags=False)
         else:
             self.bodies.ensure_packed_buffers()
+        self._moving_tables = self._build_moving_tables()
+        self._attach_moving()
         self._assert_runtime_contracts()
         self._initialized = True
 
@@ -499,6 +616,7 @@ class Simulation:
         self._require_usable()
         if not self._initialized:
             raise RuntimeError("Call initialize() before sync_bodies()")
+        self._reject_moving_bodies("sync_bodies()")
 
         self._assert_allocation_contract()
         # 1. Synchronize GPU
@@ -599,6 +717,13 @@ class Simulation:
         checkpoint_interval = operator.index(checkpoint_interval)
         if steps < 0 or checkpoint_interval < 0:
             raise ValueError("steps and checkpoint_interval must be nonnegative")
+        moving = self._moving_bodies()
+        if steps > 0 and moving and self.stepper.moving is None:
+            raise RuntimeError(MOVING_BLOCKED)
+        if moving and checkpoint_interval > 0:
+            raise ValueError("checkpoints are not supported with translating circles")
+        if steps > 1 and any(obj.motion.pending is not None for obj in moving):
+            raise ValueError("a pending translation target needs run(1)")
         self._assert_runtime_contracts()
         # Discard any uncommitted body edits before stepping.
         if self.bodies.has_pending_edit():
@@ -615,6 +740,8 @@ class Simulation:
         # Zero obs segments before step group
         if zero_obs:
             self.bodies.zero_obs_async(stream)
+            if self.stepper.moving is not None:
+                self.stepper.moving.zero_diagnostics(stream)
 
         if checkpoint_interval > 0:
             done = 0
@@ -631,6 +758,9 @@ class Simulation:
                 if done < steps or done % checkpoint_interval == 0:
                     stream.synchronize()
                     self.save_checkpoint()
+        elif self.stepper.moving is not None and steps > 0:
+            self._run_moving(steps, stream, sync_obs)
+            return
         else:
             self.stepper.step(
                 steps,
@@ -649,6 +779,34 @@ class Simulation:
 
         stream.synchronize()
 
+    def _run_moving(self, steps, stream, sync_obs):
+        """Steps with translating circles: hold, or one advancing step that commits
+        each pending target only after synchronization and a zero ``no_donor`` count
+        (docs/moving_bodies.md 4a, 5). Any failure leaves the Simulation unusable."""
+        tables = self.stepper.moving
+        circles = [(obj.motion, obj.obj_id) for obj in self._moving_bodies()]
+        try:
+            advancing = tables.upload_records(circles, stream)
+            self.stepper._step(steps, action_gpu=self.bodies.action_gpu,
+                               obs_gpu=self.bodies.obs_gpu, stream=stream, advance=advancing)
+            self.bodies.increment_obs_steps(steps)
+            if sync_obs:
+                self.bodies.download_obs_full_async(stream)
+            stream.synchronize()
+            if advancing:
+                no_donor = tables.download_diagnostics()[:, tables.DIAG.index("no_donor")]
+                if np.any(no_donor > 0):
+                    raise RuntimeError("translating circle refill found no donor cell")
+                for motion, _ in circles:
+                    motion.commit()
+                tables.upload_records(circles, stream)  # first hold: old = new = applied, u = 0
+                stream.synchronize()
+                self._attach_moving()
+        except BaseException as exc:
+            for motion, _ in circles:  # device geometry/state unknown after any failure
+                motion.fail(exc)
+            raise
+
     def step(self, n: int = 1):
         """Advance *n* steps (convenience for interactive use)."""
         self.run(n)
@@ -666,8 +824,16 @@ class Simulation:
         self.field.download_ddf(step_id=self.stepper.step_count)
         return self.field.ddf.copy()
 
+    @context_bound
     def get_flags(self) -> np.ndarray:
-        return self.field.flag.copy()
+        """Flag array; read back from the device when translating circles may have moved."""
+        if getattr(self.stepper, "moving", None) is None:
+            return self.field.flag.copy()
+        self._require_usable()
+        self.stream.synchronize()
+        flags = np.empty_like(self.field.flag)
+        cuda.memcpy_dtoh(flags, self.field.flag_gpu)
+        return flags
 
     # -- Runtime parameter updates -------------------------------------------
     @context_bound
@@ -698,6 +864,7 @@ class Simulation:
         """Save full simulation state to an HDF5 file."""
         self._require_usable()
         from .common.checkpoint import save_checkpoint
+        self._reject_moving_bodies("save_checkpoint()")
         if self.bodies.jets:
             raise NotImplementedError("Jets are not checkpointed yet")
         return save_checkpoint(self.field, self.stepper, self.lbm_cfg,
@@ -708,6 +875,7 @@ class Simulation:
         """Restore simulation state from an HDF5 checkpoint."""
         self._require_usable()
         from .common.checkpoint import load_checkpoint
+        self._reject_moving_bodies("load_checkpoint()")
         if not self._initialized:
             self.initialize()
         load_checkpoint(path, self.field, self.stepper, self.lbm_cfg,
@@ -726,6 +894,7 @@ class Simulation:
                 cuda.Context.synchronize()
                 # Release owned GPU resources while their context is current.
                 self.stepper = None
+                self._moving_tables = None
                 self.bodies = None
                 self.field = None
                 self._module = None

tests/unit/test_duetsch_protocol.py

@@ -0,0 +1,194 @@
+"""CPU tests of the Dütsch protocol arithmetic (docs/validation/duetsch_re100_kc5_protocol.md §6a)."""
+import importlib.util
+import math
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+_spec = importlib.util.spec_from_file_location(
+    "duetsch_protocol", Path(__file__).resolve().parents[2] / "research/duetsch_re100_kc5/protocol.py")
+p = importlib.util.module_from_spec(_spec)
+_spec.loader.exec_module(p)
+
+def _load(rel, name):
+    """Load a research driver module under a unique name (no bare ``import run``)."""
+    import sys
+    path = Path(__file__).resolve().parents[2] / rel
+    sys.path.insert(0, str(path.parent))  # for the driver's own sibling imports
+    try:
+        spec = importlib.util.spec_from_file_location(name, path)
+        mod = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(mod)
+    finally:
+        sys.path.remove(str(path.parent))
+    return mod
+
+
+T = 2520
+
+
+def test_phase_and_cycle_bookkeeping():
+    assert p.phase(0, T) == 270.0 and p.cycle(0, T) == 0          # +A, at rest, phi = -90
+    assert p.phase(T // 4, T) == 0.0 and p.cycle(T // 4, T) == 1  # mean position, u = -U_max
+    assert p.position(0, T, 1.0) == 1.0
+    assert p.cycle(T // 4 - 1, T) == 0 and p.cycle(T // 4 + T - 1, T) == 1
+    assert p.cycle(T // 4 + T, T) == 2
+    assert p.phase(T // 6, T) == pytest.approx(330.0) and p.cycle(T // 6, T) == 0  # startup quarter
+    assert p.phase(7 * T // 6, T) == pytest.approx(330.0) and p.cycle(7 * T // 6, T) == 1
+    for ph, frac in ((180.0, .75), (210.0, 5 / 6)):
+        s = round(frac * T) + T
+        assert p.phase(s, T) == pytest.approx(ph) and p.bin_phase(s, T) == ph
+    assert p.bin_phase(round(.75 * T) + T - 1, T) is None
+    assert sum(p.bin_phase(s, T) == 180.0 for s in range(T, 2 * T)) == T // 360
+
+
+def test_settling_and_common_window():
+    passes = {k: True for k in range(3, 12)}
+    assert p.settled_start(passes) == 7                          # pairs 3->4, 4->5, 5->6
+    late = {**passes, 5: False}
+    assert p.settled_start(late) == 9                            # pairs 6->7, 7->8, 8->9
+    assert p.common_window([7, 9], [passes, passes]) == (9, 10, 11)
+    assert p.common_window([7, 10], [passes, passes]) is None    # K + 2 = 12 beyond the cap
+    assert p.common_window([7, None], [passes, passes]) is None
+    assert p.common_window([7, 7], [passes, {**passes, 8: False}]) is None  # must stay settled
+    # a case settled early must keep passing while waiting for the common K
+    assert p.common_window([7, 9], [{**passes, 8: False}, passes]) is None
+    long = {k: True for k in range(3, 32)}
+    assert p.common_window([10], [long]) is None                 # default cap 11
+    assert p.common_window([29], [long], last_scored=31) == (29, 30, 31)
+    assert p.common_window([30], [long], last_scored=31) is None
+
+
+def test_solid_aware_bilinear():
+    field = np.arange(16.0).reshape(4, 4)
+    fluid = np.ones((4, 4), bool)
+    value, used, total = p.bilinear_fluid(field, fluid, 1.25, 1.5)
+    assert total == pytest.approx(1.0) and value == pytest.approx(0.75 * 0.5 * (5 + 9) + 0.25 * 0.5 * (6 + 10))
+    fluid[1, 1] = False                                           # one solid corner
+    value, used, total = p.bilinear_fluid(field, fluid, 1.25, 1.5)
+    assert total == pytest.approx(1.0 - 0.75 * 0.5)
+    assert all(not (i == 1 and j == 1) for i, j, _ in used)
+    assert sum(w for *_, w in used) == pytest.approx(1.0)
+    fluid[:] = False
+    assert p.bilinear_fluid(field, fluid, 1.25, 1.5) == (None, (), 0.0)
+
+
+def test_interval_bases_and_morison_fit_recover_known_coefficients():
+    b = np.array([p.interval_bases(n, T) for n in range(T // 4, T // 4 + 3 * T)])
+    phi = 2 * np.pi * (np.arange(T // 4, T // 4 + 3 * T) + .5) / T - np.pi / 2
+    assert np.allclose(b[:, 1], np.sin(phi), atol=1e-5)          # midpoint ~ interval mean
+    f = 2.09 * b[:, 0] - (math.pi ** 2 * 1.45 / p.KC) * b[:, 1]
+    assert p.morison_fit(f, b[:, 0], b[:, 1]) == pytest.approx((2.09, 1.45), abs=1e-9)
+
+
+def test_geometry_repeats_exactly_across_cycles():
+    A = p.amplitude(20)
+    for m in (0, 1, T // 4, T // 2 - 1, 7 * T // 12):
+        for c in (1, 5, 11):
+            assert p.position(m + c * T, T, A) == p.position(m, T, A)
+            assert p.phase(m + c * T, T) == p.phase(m, T)
+            v0 = p.position(m + 1, T, A) - p.position(m, T, A)
+            assert p.position(m + 1 + c * T, T, A) - p.position(m + c * T, T, A) == v0
+    assert p.cycle(T // 4 + 5 * T, T) == 6  # unwrapped index stays separate
+    assert p.interval_bases(123 + 7 * T, T) == p.interval_bases(123, T)
+
+
+def test_exact_point_inside_body_is_missing_even_with_fluid_corners():
+    field = np.zeros((6, 6))
+    fluid = np.ones((6, 6), bool)
+    fluid[3, 3] = False                         # only one corner solid
+    centre, radius = (3.0, 3.0), 0.3
+    value, used, total = p.sample(field, fluid, 3.2, 3.1, centre, radius)   # inside the circle
+    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
+    run = _load("research/duetsch_re100_kc5/run.py", "duetsch_run")
+    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"
+
+
+def _analyze():
+    return _load("research/duetsch_re100_kc5/analyze.py", "duetsch_analyze")
+
+
+def test_hf_energy_is_parseval_weighted():
+    a = _analyze()
+    n = 360
+    t = np.arange(n)
+    x = 1.0 + np.cos(2 * np.pi * 5 * t / n) + 2.0 * np.cos(2 * np.pi * 30 * t / n) + 0.5 * np.cos(np.pi * t)
+    e = a.one_sided_energy(np.fft.rfft(x), n) / n
+    assert e.sum() == pytest.approx(np.sum(x ** 2))               # Parseval
+    expected = (2.0 ** 2 / 2 + 0.5 ** 2) / np.mean(x ** 2)       # bins >= 21 (30 and Nyquist)
+    assert e[21:].sum() / e.sum() == pytest.approx(expected)
+
+
+def test_horizon_excludes_future_coverage_and_events(monkeypatch):
+    a = _analyze()
+    T, horizon = 360, 4
+    steps = round((0.25 + 6) * T)                                 # cycles 1..6 recorded
+    diag = np.zeros((steps, 15))
+    diag[round((0.25 + horizon) * T):, 13] = 1.0                  # synthetic future no_donor
+    rows = [(s, p.cycle(s, T), 180.0, 0.0, 0.0, 0.1, 0.0, 1.0) for s in range(steps)
+            if p.bin_phase(s, T) is not None and p.cycle(s, T) > p.DISCARD]
+    case = dict(path="c", D=20, T=T, box=10, n=200, u_max=.04, nu=.008, tau=.524, A=1.0,
+                steps=steps, cycles=6, F_ref=1.0, force=np.zeros((steps, 2)), diag=diag,
+                samples=np.asarray(rows, float))
+    monkeypatch.setattr(a, "load", lambda path: case)
+    out = []
+    monkeypatch.setattr("builtins.print", lambda text: out.append(text))
+    a.main(["c", "--horizon", str(horizon)])
+    import json
+    entry = json.loads(out[0])["cases"][0]
+    assert sorted(int(k) for k in entry["coverage"]) == [3, 4]   # nothing from cycles 5, 6
+    assert entry["no_donor"] == 0.0
+
+
+
+def _capture():
+    spec = importlib.util.spec_from_file_location(
+        "duetsch_capture", Path(__file__).resolve().parents[2] / "research/duetsch_re100_kc5/capture.py")
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
+
+
+def test_capture_crop_downsample_and_trends():
+    c = _capture()
+    n, D = 2400, 40
+    xm = ym = 0.5 * (n - 1)
+    A, R = p.amplitude(D), 20.0
+    box = c.crop_box(xm, ym, D, n, (xm - A - R, xm + A + R, ym - R, ym + R))
+    assert box == (880, 1520, 960, 1440) and box[1] - box[0] + 1 == 641 and box[3] - box[2] + 1 == 481
+    with pytest.raises(ValueError):
+        c.crop_box(xm, ym, D, 600, (0, 1, 0, 1))                    # leaves the domain
+    with pytest.raises(ValueError):
+        c.crop_box(xm, ym, D, n, (xm - 9 * D, xm, ym, ym))           # clips the swept body
+    field = np.arange(64.0).reshape(8, 8)
+    fluid = np.ones((8, 8), bool)
+    fluid[:4, :4] = False
+    down = c.downsample(field, fluid, 4)
+    assert np.isnan(down[0, 0]) and down[1, 1] == field[4:, 4:].mean()
+    rho = np.ones((n, n)); rho[:, 1:81] = 1.01
+    row = c.trend_row(10, 3, 180.0, rho, np.zeros((n, n)), np.zeros((n, n)),
+                      np.ones((n, n), bool), D, n, box)
+    assert row[7] == pytest.approx(1.01) and row[9] == pytest.approx(1.0)
+
+
+def test_dump_steps_are_the_first_step_of_each_bin():
+    T = 5040
+    for k in (11, 21, 30, 31):
+        starts = [s for s in range(T // 4 + (k - 1) * T, T // 4 + k * T)
+                  if p.bin_phase(s, T) is not None and p.phase(s, T) == p.bin_phase(s, T)]
+        assert len(starts) == 3 and all(p.cycle(s, T) == k for s in starts)

tests/unit/test_moving_bodies.py

@@ -0,0 +1,536 @@
+"""Translating-circle host contract, S1 (docs/moving_bodies.md 4a, 5, 7).
+
+Host doubles only: no kernels exist yet, so every positive-step run with a
+moving body must be rejected before any device write.
+"""
+from types import SimpleNamespace
+
+import pytest
+
+from CelerisLab.body.motion import (MAX_STEP, R_MIN, MovingCircle, Translation,
+                                    enumerate_donor_coverage)
+
+BAD = (float("nan"), float("inf"))
+
+
+def circle(box=(-2., 2., -3., 3.), speed=.1):
+    return MovingCircle((50., 40.), 10., Translation(box, speed))
+
+
+def test_translation_and_radius_validation():
+    for box in ((0., 1., -1., 1.)[:3], (.5, 1., -1., 1.), (-1., 1., BAD[0], 1.)):
+        with pytest.raises(ValueError):
+            Translation(box, .1)
+    for speed in (0., MAX_STEP + 1e-9) + BAD:
+        with pytest.raises(ValueError):
+            Translation((0., 0., -1., 1.), speed)
+    with pytest.raises(ValueError):
+        MovingCircle((0., 0.), R_MIN - .1, Translation((0., 0., -1., 1.), .1))
+
+
+def test_targets_validate_against_applied_and_last_wins():
+    c = circle()
+    c.set_target((0., .3), (0., .05))
+    c.set_target((0., .5), (0., .05))  # second setter replaces, checked vs applied (0, 0)
+    assert c.pending == ((0., .5), (0., .05))
+    for offset, velocity in (((0., .51), (0., 0.)),           # Euclidean bound
+                             ((.36, .36), (0., 0.)),          # |dc|_2 = .509
+                             ((0., 3.1), (0., 0.)),           # outside box
+                             ((0., .1), (0., .11)),           # speed bound
+                             ((0., 0.), (0., .01)),           # hold with sliding velocity
+                             ((BAD[0], 0.), (0., 0.)), ((0., 0.), (0., BAD[1]))):
+        with pytest.raises(ValueError):
+            c.set_target(offset, velocity)
+        assert c.pending == ((0., .5), (0., .05))  # invalid replacement keeps the old target
+    c.set_target((.35, .35), (0., 0.))  # |dc|_2 = .495 inside the bound
+    assert c.applied == (0., 0.)
+
+
+def test_record_commit_and_hold():
+    c = circle()
+    assert c.record() == ((50., 40.), (50., 40.), (0., 0.))  # hold: no translation velocity
+    c.set_target((0., .25), (0., .05))
+    assert c.record() == ((50., 40.), (50., 40.25), (0., .05))
+    uploads = []
+    c.advance(uploads.append, lambda: None, lambda: None)
+    assert uploads == [((50., 40.), (50., 40.25), (0., .05))]
+    assert c.applied == (0., .25) and c.pending is None  # offset-only commit
+    c.advance(uploads.append, lambda: None, lambda: None)  # no new target: hold step
+    assert uploads[-1] == ((50., 40.25), (50., 40.25), (0., 0.)) and c.applied == (0., .25)
+    c.set_target((0., 0.), (0., -.05))  # return to zero offset is a real target
+    assert c.pending == ((0., 0.), (0., -.05))
+    c.advance(uploads.append, lambda: None, lambda: None)
+    assert c.applied == (0., 0.) and c.pending is None
+
+
+@pytest.mark.parametrize("stage", ("upload", "step", "synchronize"))
+def test_failure_after_upload_attempt_is_fail_closed(stage):
+    c = circle()
+    c.set_target((0., .25), (0., .05))
+
+    def call(name):
+        def run(*_):
+            if name == stage:
+                raise RuntimeError(f"{name} failed")
+        return run
+    with pytest.raises(RuntimeError, match=f"{stage} failed"):
+        c.advance(call("upload"), call("step"), call("synchronize"))
+    assert c.failed and c.applied == (0., 0.)
+    for later in (c.record, lambda: c.set_target((0., .1), (0., 0.)),
+                  lambda: c.advance(*(lambda *_: None,) * 3)):
+        with pytest.raises(RuntimeError, match="unknown"):
+            later()
+
+
+def test_band_covers_offset_box_with_margin():
+    assert circle().band() == (50 - 2 - 10 - 2, 50 + 2 + 10 + 2, 40 - 3 - 10 - 2, 40 + 3 + 10 + 2)
+
+
+@pytest.mark.parametrize("radius", (R_MIN, 4.3, 7.5, 12.0))
+def test_refill_donor_sets_nonempty_within_bounds(radius):
+    # Evidence for R >= R_MIN and |dc|_2 <= MAX_STEP on a fixed sample, not a proof.
+    assert enumerate_donor_coverage(radius) == 0
+
+
+pytest.importorskip("pycuda.driver")
+from CelerisLab import simulation as module  # noqa: E402
+from tests.unit.test_simulation_lifecycle import Owner, make_simulation  # noqa: E402
+
+
+class ClosableOwner(Owner):
+    """Owner double that refuses activation after close, like CudaContext.activate."""
+    def activate(self):
+        if self.is_closed:
+            raise RuntimeError("CUDA context is closed")
+        return super().activate()
+
+
+def moving_simulation(monkeypatch, *, moving=True):
+    sim = make_simulation(monkeypatch)
+    obj = SimpleNamespace(motion=circle() if moving else None, obj_id=0,
+                          center=(50., 40.), radius=10.)
+    writes = []
+    sim._failed, sim._initialized = None, True
+    sim.bodies = SimpleNamespace(objects=[obj], count=1, jets=[], action_gpu=None, obs_gpu=None,
+                                 has_pending_edit=lambda: False,
+                                 _upload_action_async=lambda s: writes.append("action"),
+                                 zero_obs_async=lambda s: writes.append("obs"),
+                                 increment_obs_steps=lambda n: writes.append("count"),
+                                 download_obs_full_async=lambda s: writes.append("download"))
+    sim.stepper = SimpleNamespace(step=lambda n, **k: writes.append(("step", n)), blocked=None,
+                                  moving=None)
+    sim._assert_runtime_contracts = lambda: None
+    return sim, writes
+
+
+STREAM = SimpleNamespace(synchronize=lambda: None)
+
+
+def test_positive_steps_rejected_before_device_writes(monkeypatch):
+    sim, writes = moving_simulation(monkeypatch)
+    sim.bodies.objects[0].motion.set_target((0., .1), (0., .01))
+    sim.bodies.objects[0].motion.applied = (0., 0.)
+    for call in (lambda: sim.run(1, stream=STREAM), lambda: sim.run(5, stream=STREAM),
+                 lambda: sim.step(), lambda: sim.run(3, stream=STREAM, checkpoint_interval=1)):
+        with pytest.raises(RuntimeError, match="moving kernels"):
+            call()
+    with pytest.raises(RuntimeError, match="moving kernels"):  # nominal at rest as well
+        sim.bodies.objects[0].motion.pending = None
+        sim.run(1)
+    sim.bodies.objects[0].state = SimpleNamespace(omega=.02)  # spin does not lift the guard
+    with pytest.raises(RuntimeError, match="moving kernels"):
+        sim.run(2, stream=STREAM)
+    assert writes == [] and sim.bodies.objects[0].motion.applied == (0., 0.)
+
+
+def test_run_zero_keeps_pending_and_static_runs_proceed(monkeypatch):
+    sim, writes = moving_simulation(monkeypatch)
+    motion = sim.bodies.objects[0].motion
+    motion.set_target((0., .1), (0., .01))
+    sim.run(0, stream=STREAM)  # existing action/obs work only; no motion upload or commit
+    assert motion.pending == ((0., .1), (0., .01)) and motion.applied == (0., 0.)
+    assert ("step", 0) in writes
+    static, writes = moving_simulation(monkeypatch, moving=False)
+    static.save_checkpoint = lambda *a: writes.append("checkpoint")
+    static.run(3, stream=STREAM)
+    static.run(4, stream=STREAM, checkpoint_interval=2)
+    assert writes.count(("step", 3)) == 1 and writes.count(("step", 2)) == 2
+
+
+def test_direct_stepper_entry_is_guarded():
+    from CelerisLab.lbm.stepper import LBMStepper
+    launches = []
+    module = SimpleNamespace(get_function=lambda name: lambda *a, **k: launches.append(name))
+    cfg = SimpleNamespace(streaming="double_buffer", threads_per_block=128, is_d2q9=True,
+                          nx=64, ny=32, nz=1)
+    field = SimpleNamespace(ddf_gpu="ddf", temp_gpu="temp", n_curved=0)
+    stepper = LBMStepper(field, module, cfg)
+    assert stepper.blocked is None
+    stepper.blocked = "translating circles need the moving kernels"
+    for n in (1, 3):
+        with pytest.raises(RuntimeError, match="moving kernels"):
+            stepper.step(n, action_gpu=None, obs_gpu=None)
+    assert launches == [] and (field.ddf_gpu, field.temp_gpu) == ("ddf", "temp")
+    assert stepper.step_count == 0
+    stepper.step(0, action_gpu=None, obs_gpu=None)  # zero steps stay a no-op
+    assert launches == [] and stepper.step_count == 0
+
+
+def test_moving_body_rejects_topology_and_checkpoint(monkeypatch):
+    sim, _ = moving_simulation(monkeypatch)
+    for call in (sim.sync_bodies, sim.save_checkpoint, lambda: sim.load_checkpoint("x.h5")):
+        with pytest.raises(ValueError, match="translating circles"):
+            call()
+
+
+# -- Real-object routing, initialize rejections, packing, lifecycle -------------
+import numpy as np  # noqa: E402
+
+from CelerisLab.body.geometry.circle import CircleGeometry  # noqa: E402
+from CelerisLab.body.manager import ObjectManager  # noqa: E402
+from CelerisLab.body.objects import SimObject  # noqa: E402
+from CelerisLab.lbm.descriptors import FLUID, SOLID  # noqa: E402
+
+
+class Cfg:
+    dim, is_d3q19, is_d2q9 = 2, False, True
+    streaming, ddf_shifting, store_precision, y_wall_bc = "double_buffer", False, "FP32", "bounce_back"
+
+
+def body(x, y, r, translation=None, **kw):
+    obj = SimObject(obj_id=-1, geometry=CircleGeometry(x, y, r), center=(x, y), radius=r, **kw)
+    if translation is not None:
+        obj.motion = MovingCircle((x, y), r, translation)
+    return obj
+
+
+def routed_simulation(monkeypatch):
+    sim = make_simulation(monkeypatch)
+    sim._failed, sim._initialized, sim.lbm_cfg = None, False, Cfg()
+    sim.stepper = SimpleNamespace(blocked=None)
+    sim.bodies = ObjectManager(nx=120, ny=80, nz=1, nq=9, cfg=Cfg())
+    return sim
+
+
+def test_add_body_and_set_body_route_targets(monkeypatch):
+    sim = routed_simulation(monkeypatch)
+    bid = sim.add_body("circle", (50., 40.), 10., translation=Translation((-2., 2., -3., 3.), .1))
+    still = sim.add_body("circle", (100., 40.), 5.)
+    motion = sim.bodies.get(bid).motion
+    sim._moving_tables = "tables"
+    sim._attach_moving()
+    assert sim.stepper.blocked is None
+    sim.set_body(bid, offset=(0., .3), vy=.05)
+    assert sim.stepper.blocked == module.PENDING_BLOCKED  # direct steps never consume a target
+    sim.set_body(bid, offset=(0., .4), vy=.05)  # last wins
+    for kwargs in (dict(offset=(0., .6)), dict(vy=.05), dict(vx=.05),
+                   dict(offset=(0., .1), vy=.2), dict(offset=(0., 0.), vy=.01)):
+        with pytest.raises(ValueError):
+            sim.set_body(bid, **kwargs)
+        assert motion.pending == ((0., .4), (0., .05))  # invalid input keeps the target
+    sim.set_body(bid, omega=.01)  # omega-only keeps the pending target
+    obj = sim.bodies.get(bid)
+    assert obj.state.omega == .01 and (obj.state.vx, obj.state.vy) == (0., 0.)
+    assert motion.pending == ((0., .4), (0., .05)) and motion.applied == (0., 0.)
+    with pytest.raises(ValueError, match="not declared"):
+        sim.set_body(still, offset=(0., .1))
+    sim.set_body(still, vx=.01)  # stationary API unchanged
+    assert sim.bodies.get(still).state.vx == .01 and sim.bodies.get(still).motion is None
+    for kwargs in (dict(type="sensor"), dict(surface_actuation=dict(angle=0., half_width=.2,
+                                                                    normal_velocity=.01))):
+        kind = kwargs.pop("type", "circle")
+        with pytest.raises(ValueError, match="translation"):
+            sim.add_body(kind, (20., 20.), 5., translation=Translation((0., 0., 0., 0.), .1),
+                         **kwargs)
+
+
+class Tables:
+    """MovingTables double: records uploads, steps and diagnostics reads."""
+    DIAG = ("no_donor",)
+
+    def __init__(self, log, no_donor=0., fail=None):
+        self.log, self.no_donor, self.fail = log, no_donor, fail
+
+    def upload_records(self, circles, stream):
+        records = [m.record() for m, _ in circles]
+        self.log.append(("upload", records))
+        uploads = sum(1 for w in self.log if isinstance(w, tuple) and w[0] == "upload")
+        if self.fail == "upload" or (self.fail == "hold_upload" and uploads == 2):
+            raise RuntimeError("upload failed")
+        return any(r[0] != r[1] for r in records)
+
+    def zero_diagnostics(self, stream):
+        self.log.append("zero_diag")
+
+    def download_diagnostics(self):
+        return np.array([[self.no_donor]], np.float32)
+
+
+def advancing_simulation(monkeypatch, **tables):
+    sim, writes = moving_simulation(monkeypatch)
+    sim.bodies.objects[0].motion = circle()
+    sim.stepper = SimpleNamespace(
+        moving=Tables(writes, **tables), blocked=None,
+        _step=lambda n, advance=False, **k: writes.append(("step", n, advance)))
+    from CelerisLab.lbm.stepper import LBMStepper
+    sim.stepper.step = LBMStepper.step.__get__(sim.stepper)  # real public entry
+    sim._moving_tables = sim.stepper.moving
+    return sim, writes, sim.bodies.objects[0].motion
+
+
+def test_run_one_advances_and_commits_after_sync(monkeypatch):
+    sim, writes, motion = advancing_simulation(monkeypatch)
+    motion.set_target((0., .25), (0., .05))
+    with pytest.raises(ValueError, match="run\\(1\\)"):  # multi-step with a target
+        sim.run(2, stream=STREAM)
+    assert writes == [] and motion.pending is not None
+    sim.run(0, stream=STREAM)  # zero steps never consume the target
+    assert motion.pending is not None
+    sim.run(1, stream=STREAM)
+    uploads = [w for w in writes if isinstance(w, tuple) and w[0] == "upload"]
+    assert uploads[0][1] == [((50., 40.), (50., 40.25), (0., .05))]
+    assert uploads[1][1] == [((50., 40.25), (50., 40.25), (0., 0.))]  # first hold after move
+    assert ("step", 1, True) in writes
+    assert motion.applied == (0., .25) and motion.pending is None
+    writes.clear()
+    sim.run(3, stream=STREAM)  # hold steps: no advance
+    assert ("step", 3, False) in writes and motion.applied == (0., .25)
+
+
+@pytest.mark.parametrize("failure", ("upload", "first_sync", "no_donor", "hold_upload",
+                                     "hold_sync"))
+def test_failed_advance_fails_simulation(monkeypatch, failure):
+    kwargs = dict(no_donor=1.) if failure == "no_donor" else dict(fail=failure)
+    sim, writes, motion = advancing_simulation(monkeypatch, **kwargs)
+    motion._on_failure = sim._fail_moving
+    motion.set_target((0., .25), (0., .05))
+    syncs = []
+
+    def synchronize():  # stands in for an asynchronous failure surfacing at sync
+        syncs.append(1)
+        if (failure, len(syncs)) in (("first_sync", 1), ("hold_sync", 2)):
+            raise RuntimeError("sync failed")
+    with pytest.raises(RuntimeError):
+        sim.run(1, stream=SimpleNamespace(synchronize=synchronize))
+    # Before the step-group sync and no_donor check nothing is committed; the hold
+    # record is staged after the commit (applied already matches the moved device).
+    committed = failure in ("hold_upload", "hold_sync")
+    assert motion.applied == ((0., .25) if committed else (0., 0.))
+    assert (motion.pending is None) == committed
+    assert motion.failed and sim._failed is not None
+    assert sim.stepper.blocked == sim._failed  # direct stepper reuse refused too
+    with pytest.raises(RuntimeError, match="Simulation failed"):
+        sim.run(1, stream=STREAM)
+
+
+def test_failed_hold_step_blocks_the_direct_stepper(monkeypatch):
+    # No target is pending, so only the failure latch can refuse direct steps.
+    from CelerisLab.lbm.stepper import LBMStepper
+    sim, writes, motion = advancing_simulation(monkeypatch, fail="upload")
+    motion._on_failure = sim._fail_moving
+    launches = []
+    kernels = SimpleNamespace(get_function=lambda name: lambda *a, **k: launches.append(name))
+    cfg = SimpleNamespace(streaming="double_buffer", threads_per_block=128, is_d2q9=True,
+                          nx=64, ny=32, nz=1)
+    field = SimpleNamespace(ddf_gpu="ddf", temp_gpu="temp", flag_gpu="flag", n_curved=0)
+    stepper = LBMStepper(field, kernels, cfg)
+    stepper.moving = sim.stepper.moving
+    sim.stepper = stepper
+    assert motion.pending is None and stepper.blocked is None
+    with pytest.raises(RuntimeError, match="upload failed"):
+        sim.run(2, stream=STREAM)  # hold step
+    assert sim._failed is not None and stepper.blocked == sim._failed
+    with pytest.raises(RuntimeError, match="moving circle step failed"):
+        stepper.step(1, action_gpu=None, obs_gpu=None)
+    assert launches == [] and stepper.step_count == 0
+    assert (field.ddf_gpu, field.temp_gpu) == ("ddf", "temp")
+
+
+def test_moving_tables_layout_and_attachment(monkeypatch):
+    from CelerisLab.body.motion import MovingTables
+    a = MovingCircle((50., 40.), 10., Translation((-1., 1., -3., 3.), .1))
+    b = MovingCircle((90.25, 30.5), 5., Translation((0., 0., 0., 0.), .1))
+    band, geom = MovingTables.layout([(a, 2), (b, 5)])
+    wa, ha = 63 - 37 + 1, 55 - 25 + 1
+    assert band == [37, 25, wa, ha, 0, 2, 83, 23, 16, 16, wa * ha * 8, 5]
+    assert geom == [50., 40., 50., 40., 10., 0., 0., 90.25, 30.5, 90.25, 30.5, 5., 0., 0.]  # hold
+    sim = routed_simulation(monkeypatch)
+    sim.add_body("circle", (50., 40.), 10., translation=Translation((0., 0., 0., 0.), .1))
+    sim._moving_tables = "tables"
+    sim._attach_moving()
+    assert sim.stepper.moving == "tables" and sim.stepper.blocked is None
+    sim._moving_tables = None
+    sim._attach_moving()
+    assert sim.stepper.moving is None and sim.stepper.blocked is not None
+
+
+class CountingOwner(Owner):
+    """Owner double that counts nested activations like CudaContext."""
+    def __init__(self):
+        super().__init__()
+        self.active = 0
+
+    def activate(self):
+        from contextlib import contextmanager
+
+        @contextmanager
+        def scope():
+            self.active += 1
+            try:
+                yield self
+            finally:
+                self.active -= 1
+        return scope()
+
+
+def test_public_diagnostics_keep_owner_active_through_sync_and_download(monkeypatch):
+    sim = make_simulation(monkeypatch)
+    sim.ctx, sim._failed = CountingOwner(), None
+    seen = []
+    sim._stream = SimpleNamespace(synchronize=lambda: seen.append(("sync", sim.ctx.active)))
+    expected = np.arange(6, dtype=np.float32).reshape(1, 6)
+
+    def download():
+        seen.append(("download", sim.ctx.active))
+        return expected
+    sim.stepper = SimpleNamespace(moving=SimpleNamespace(download_diagnostics=download))
+    assert sim.moving_diagnostics() is expected
+    assert [name for name, _ in seen] == ["sync", "download"]
+    assert all(active > 0 for _, active in seen) and sim.ctx.active == 0
+
+
+def test_stepper_launches_moving_links_before_static_curved():
+    from CelerisLab.lbm.stepper import LBMStepper
+    launches = []
+    module = SimpleNamespace(get_function=lambda name: lambda *a, **k: launches.append((name, a, k)))
+    cfg = SimpleNamespace(streaming="double_buffer", threads_per_block=128, is_d2q9=True,
+                          nx=64, ny=32, nz=1)
+    curved = SimpleNamespace(**{f"{name}_gpu": name for name in (
+        "fluid_idx", "dir", "q", "rx", "ry", "rz", "fallback_class", "body_id")},
+        surface_velocity=None, surface_velocity_gpu=None, link_exchange_gpu=None)
+    field = SimpleNamespace(ddf_gpu="ddf", temp_gpu="temp", flag_gpu="flag", n_curved=5,
+                            curved=curved, invalidate_host_ddf_cache=lambda: None)
+    stepper = LBMStepper(field, module, cfg)
+    stepper._launch_force_region = stepper._launch_sensor = lambda *a, **k: None
+    stepper.moving = SimpleNamespace(band_gpu="band", geom_gpu="geom", diag_gpu="diag",
+                                     slot_debug_gpu=None, n_bodies=1, n_slots=300)
+    stepper.step(2, action_gpu="act", obs_gpu="obs")
+    names = [name for name, _, _ in launches]
+    assert names == ["MovingCircleLinks", "CurvedBoundaryKernel", "OneStep"] * 2
+    assert stepper.step_count == 2
+    assert launches[1][1][0] == "ddf" and launches[3][1][0] == "temp"  # swap between steps
+    args, kw = launches[0][1], launches[0][2]
+    assert args[:4] == ("ddf", "flag", "band", "geom") and int(args[5]) == 300
+    assert kw["grid"] == (3, 1, 1) and kw["block"] == (128, 1, 1)
+
+
+def test_recompile_installs_a_guarded_stepper(monkeypatch):
+    from CelerisLab.lbm.stepper import LBMStepper
+    sim = routed_simulation(monkeypatch)
+    sim.add_body("circle", (50., 40.), 10., translation=Translation((0., 0., -1., 1.), .1))
+    launches = []
+    kernel_module = SimpleNamespace(get_function=lambda name: lambda *a, **k: launches.append(name))
+    monkeypatch.setattr(module.compiler, "build_module", lambda *a, **k: kernel_module)
+    sim.lbm_cfg = SimpleNamespace(validate_runtime=lambda: None, viscosity=.01, omega=1.,
+                                  streaming="double_buffer", threads_per_block=128,
+                                  is_d2q9=True, nx=120, ny=80, nz=1)
+    sim._compiled_viscosity = .01
+    sim._assert_allocation_contract = lambda: None
+    sim._resolve_compile_arch = lambda: "sm_70"
+    sim._assert_object_count_contract = lambda **k: None
+    sim.field = SimpleNamespace(module=None, invalidate_module_constant_cache=lambda: None,
+                                _upload_params=lambda: None, _runtime_params={},
+                                ddf_gpu="ddf", temp_gpu="temp", n_curved=0)
+    sim.stepper = SimpleNamespace(_step_count=7, blocked=None)
+    sim._recompile()
+    assert isinstance(sim.stepper, LBMStepper) and sim.stepper.step_count == 7
+    with pytest.raises(RuntimeError, match="moving kernels"):
+        sim.stepper.step(1, action_gpu=None, obs_gpu=None)
+    assert launches == [] and (sim.field.ddf_gpu, sim.field.temp_gpu) == ("ddf", "temp")
+    assert sim.stepper.step_count == 7
+
+
+def validate(monkeypatch, objects, flags=None, **cfg):
+    sim = routed_simulation(monkeypatch)
+    for obj in objects:
+        sim.bodies.add(obj)
+    for name, value in cfg.items():
+        setattr(sim.lbm_cfg, name, value)
+    base = np.full(120 * 80, FLUID, np.uint16) if flags is None else flags
+    sim.field = SimpleNamespace(nx=120, ny=80, build_channel_flags=lambda: base.copy())
+    sim._validate_moving_bodies()
+
+
+def test_initialize_rejects_band_and_modes(monkeypatch):
+    t = Translation((-1., 1., -3., 3.), .1)
+    validate(monkeypatch, [body(50., 40., 10., t), body(100., 40., 5.)])  # accepted
+    walls = np.full(120 * 80, FLUID, np.uint16)
+    walls[60 + 30 * 120] = SOLID
+    cases = [([body(10., 40., 10., t)], None, {}, "domain edge"),
+             ([body(50., 40., 10., t)], walls, {}, "non-fluid"),
+             ([body(50., 40., 10., t), body(68., 40., 4.)], None, {}, "overlaps"),
+             ([body(50., 40., 10., t), body(50., 60., 3., is_sensor=True)], None, {}, "overlaps"),
+             ([body(50., 40., 10., t), body(64., 40., 3., is_force_region=True)], None, {}, "overlaps"),
+             ([body(50., 40., 10., t)], None, {"streaming": "esopull"}, "double_buffer"),
+             ([body(50., 40., 10., t)], None, {"ddf_shifting": True}, "unshifted"),
+             ([body(50., 40., 10., t)], None, {"is_d2q9": False}, "D2Q9")]
+    for objects, flags, cfg, match in cases:
+        with pytest.raises(ValueError, match=match):
+            validate(monkeypatch, objects, flags, **cfg)
+
+
+def test_initialize_validates_before_mutation(monkeypatch):
+    sim = routed_simulation(monkeypatch)
+    sim.bodies.add(body(10., 40., 10., Translation((0., 0., 0., 0.), .1)))
+    uploads = []
+    sim.field = SimpleNamespace(nx=120, ny=80, build_channel_flags=lambda: np.full(9600, FLUID, np.uint16),
+                                upload_flags=lambda: uploads.append("flags"))
+    sim._assert_allocation_contract = lambda: None
+    with pytest.raises(ValueError, match="domain edge"):
+        sim.initialize()
+    assert uploads == [] and not sim._initialized
+
+
+def test_moving_circle_excluded_from_static_links():
+    def manager(*objects):
+        mgr = ObjectManager(nx=120, ny=80, nz=1, nq=9, cfg=Cfg())
+        ids = [mgr.add(obj) for obj in objects]
+        return mgr, ids
+    reference_mgr, _ = manager(body(100., 40., 5.), body(20., 40., 6.))
+    mixed_mgr, ids = manager(body(100., 40., 5.), body(20., 40., 6.),
+                             body(55., 40., 10., Translation((0., 0., -1., 1.), .1)))
+    reference = reference_mgr.build_compact_lists_for(reference_mgr.objects)
+    mixed = mixed_mgr.build_compact_lists_for(mixed_mgr.objects)
+    for a, b in zip(reference[:8], mixed[:8]):  # static link columns byte-identical
+        assert np.asarray(a).tobytes() == np.asarray(b).tobytes()
+    assert len(reference[0]) > 0 and ids[2] not in set(np.asarray(mixed[3]).tolist())
+
+
+def test_failed_moving_step_marks_simulation_failed(monkeypatch):
+    sim = routed_simulation(monkeypatch)
+    sim.ctx = ClosableOwner()
+    bid = sim.add_body("circle", (50., 40.), 10., translation=Translation((0., 0., -1., 1.), .1))
+    motion = sim.bodies.get(bid).motion
+    motion.set_target((0., .2), (0., .05))
+
+    def fail(*_):
+        raise RuntimeError("sync failed")
+    with pytest.raises(RuntimeError, match="sync failed"):
+        motion.advance(lambda *_: None, lambda: None, fail)
+    assert sim._failed is not None and motion.applied == (0., 0.)
+    for call in (lambda: sim.run(0), lambda: sim.run(1), sim.step, sim.sync_bodies,
+                 sim.save_checkpoint, lambda: sim.load_checkpoint("x.h5")):
+        with pytest.raises(RuntimeError, match="Simulation failed"):
+            call()
+    with pytest.raises(RuntimeError, match="unknown"):  # no retry on the failed circle
+        motion.advance(lambda *_: None, lambda: None, lambda: None)
+    with sim.ctx.activate():  # a refused close keeps the failed state and resources
+        with pytest.raises(RuntimeError, match="active CUDA"):
+            sim.close()
+    assert sim._failed is not None and sim.bodies is not None and not sim._closed
+    sim.close()  # retry outside the activation succeeds
+    assert sim._closed and sim._failed is not None
+    with pytest.raises(RuntimeError, match="CUDA context is closed"):  # no re-entry after close
+        sim.run(1)
+    with pytest.raises(RuntimeError, match="unknown"):  # the failed circle stays refused
+        motion.record()

tests/unit/test_state_regressions.py

@@ -294,8 +294,11 @@ def test_passive_overlap_failure_keeps_live_state(device, entry, second_x):
     sim = SimpleNamespace(bodies=bodies, field=field, lbm_cfg=field.cfg,
                           _initialized=entry == "runtime_edit",
                           _assert_allocation_contract=lambda: None,
-                          stream=SimpleNamespace(synchronize=device.synchronize))
-    sim._require_usable = Simulation._require_usable.__get__(sim)
+                          stream=SimpleNamespace(synchronize=device.synchronize),
+                          stepper=SimpleNamespace(blocked=None))
+    for name in ("_require_usable", "_moving_bodies", "_reject_moving_bodies",
+                 "_validate_moving_bodies", "_attach_moving"):
+        setattr(sim, name, getattr(Simulation, name).__get__(sim))
     with pytest.raises(ValueError, match="active fluid receivers|unique cut-link writers"):
         if entry == "sync":
             bodies.sync_to_gpu(field)

tests/unit/test_viv_logic.py

@@ -0,0 +1,105 @@
+"""CPU tests of the predeclared VIV logic (research/viv_re150/viv.py; stdlib only)."""
+import importlib.util
+import math
+from pathlib import Path
+
+_spec = importlib.util.spec_from_file_location(
+    "viv_logic", Path(__file__).resolve().parents[2] / "research/viv_re150/viv.py")
+viv = importlib.util.module_from_spec(_spec)
+_spec.loader.exec_module(viv)
+
+def _load(rel, name):
+    """Load a research driver module under a unique name (no bare ``import run``)."""
+    import sys
+    path = Path(__file__).resolve().parents[2] / rel
+    sys.path.insert(0, str(path.parent))  # for the driver's own sibling imports
+    try:
+        spec = importlib.util.spec_from_file_location(name, path)
+        mod = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(mod)
+    finally:
+        sys.path.remove(str(path.parent))
+    return mod
+
+
+D, U = 40, 0.04
+
+
+def _feed(cyc, amps, period=100):
+    """Feed sine cycles of the given amplitudes (in D); return the first non-None result."""
+    n = 0
+    for a in amps:
+        for i in range(period):
+            out = cyc.update(a * D * math.sin(2 * math.pi * (i + 1) / period))
+            n += 1
+            if out:
+                return out, n
+    return None, n
+
+
+def test_structure_exact_update_conserves_free_oscillation_and_equilibrium():
+    s = viv.Structure(D, U)
+    assert math.isclose(1 / s.f_n, 5000.0) and math.isclose(s.m, 2 * D * D)
+    s.y, s.v = 0.3 * D, 0.0
+    e0 = 0.5 * s.k * s.y ** 2
+    for _ in range(12345):
+        s.y, s.v = s.candidate(0.0)
+    assert math.isclose(0.5 * s.k * s.y ** 2 + 0.5 * s.m * s.v ** 2, e0, rel_tol=1e-9)
+    s.y, s.v = 2.0 / s.k, 0.0
+    assert all(math.isclose(a, b, abs_tol=1e-12) for a, b in zip(s.candidate(2.0), (2.0 / s.k, 0.0)))
+    assert math.isclose(s.seed_velocity(D) / s.w, viv.ELIGIBLE * D)
+
+
+def test_constant_amplitude_settles_then_scores_twenty_cycles():
+    cyc = viv.Cycles(D)
+    out, _ = _feed(cyc, [0.5] * 60)
+    assert out == "scored" and len(cyc.window) == 20 and cyc.settled_at == 1
+    r = viv.score(cyc.window)
+    assert math.isclose(r["A_max"], 0.5, rel_tol=1e-3) and abs(r["offset"]) < 1e-3
+    assert r["T_resp"] == 100 and r["within_band"]          # |.500 - .520| <= .052
+
+
+def test_small_cycles_are_not_counted_and_y0_is_not_a_crossing():
+    cyc = viv.Cycles(D)
+    assert cyc.update(0.0) is None and cyc.log == []
+    out, _ = _feed(cyc, [0.005] * 50)
+    assert out is None and cyc.counted == 0 and cyc.log and not any(c["eligible"] for c in cyc.log)
+
+
+def test_scoring_failure_restarts_from_the_failing_block():
+    cyc = viv.Cycles(D)
+    amps = [0.5] * 20 + [0.55] * 10 + [0.55] * 40      # settle at block 1, block 2 jumps 10 %
+    out, _ = _feed(cyc, amps)
+    assert out == "scored"
+    assert all(math.isclose(c["amp"], 0.55, rel_tol=1e-3) for c in cyc.window)
+
+
+def test_seed_reset_discards_incomplete_cycle_and_proof():
+    cyc = viv.Cycles(D)
+    _feed(cyc, [0.5] * 15)
+    cyc.update(0.2 * D)                                  # inside an incomplete cycle
+    counted = cyc.counted
+    cyc.discard_current()
+    cyc.reset_proof()
+    assert cyc.amps == [] and cyc.blocks == [] and cyc.counted == counted
+
+
+def test_viv_config_passes_the_real_loader(tmp_path):
+    import json
+    run = _load("research/viv_re150/run.py", "viv_run")
+    from CelerisLab.config import load_lbm_config
+    cfg_dict, nx, ny = run.config()
+    path = tmp_path / "config_lbm.json"
+    path.write_text(json.dumps(cfg_dict))
+    cfg = load_lbm_config(str(path))
+    assert (cfg.nx, cfg.ny) == (nx, ny) == (3000, 2400)
+    assert cfg.collision == "MRT" and cfg.y_wall_bc == "free_slip" and cfg.velocity == .04
+    assert math.isclose(cfg.viscosity, .04 * 40 / 150)
+
+
+def test_finite_rejects_any_nonfinite_recorded_output():
+    row = (3, .1, .2, .3, .4, .5, .6, .7, 0.0)
+    assert viv.finite(row)
+    for i in range(len(row)):
+        for bad in (float("nan"), float("inf"), -float("inf")):
+            assert not viv.finite(row[:i] + (bad,) + row[i + 1:])