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"""End-to-end Q2_K pipeline preserving the HPC machinery.

Pipeline stages (mirroring the C engine, with V2 fixes):

1. kurtosis-gated outlier clamp and batched GGML seeds;
2. vectorised WLS superblock solve;
3. factored candidate field + standalone factored floor;
4. sequential Sieve over coarse/fine symbolic states;
5. 36-state Viterbi sequence optimisation;
6. candidate-aware factor consistency pass;
7. rolling DC residual carry;
8. sub-block Sieve assembly, LS refit, fp16-ULP polish, spectral shaping;
9. objective-consistent local-safety floors and DC nudge.
"""

from __future__ import annotations

from dataclasses import dataclass
from math import ceil
import multiprocessing as mp
import os
import time

import numpy as np

from .anneal import thermal_refine_tensor
from .config import HPCConfig
from .factored import (
    CAND_TO_QUHIT,
    MULTS_D,
    MULTS_M,
    N_CAND_M,
    TOTAL_CANDIDATES,
    FactorResult,
    candidate_pair,
    factor_candidates,
    factor_only_solve,
    factor_q2k_block,
)
from .fp16 import from_fp16_bits, nearest_int, round_fp16, to_fp16_bits
from .q2k import (
    NS,
    QK_K,
    Q2KBlock,
    codes_from_params,
    codes_from_params_batch,
    dequantize_params,
    dequantize_params_batch,
    derive_subscales,
    make_block,
    pack_codes,
    pack_scales,
    pin_q2k_dc_residual,
    unpack_codes,
    weighted_sse,
)
from .seeds import block_clamp_values, build_seeds, seed_clamp_value
from .sieve import block_chain_edges, sieve_measure_chain, subblock_chain_edges
from .spectral import dc_nudge_codes, fold_weights, objective, refine_codes_hadamard
from .viterbi import robust_temperature, viterbi_select


@dataclass(slots=True)
class TensorStats:
    n_blocks: int
    total_sse: float
    weighted_sse: float
    rmse: float
    sigma: float
    rmse_over_sigma: float
    temperature: float
    factor_floor_used: int
    candidate_floor_used: int
    therm_improved: int = 0


@dataclass(slots=True)
class QuantizedTensor:
    blocks: list[Q2KBlock]
    scales: np.ndarray
    qs: np.ndarray
    dm: np.ndarray
    best_candidate: np.ndarray
    factor_objectives: np.ndarray
    config: HPCConfig
    stats: TensorStats

    def dequantize(self) -> np.ndarray:
        return np.concatenate([b.dequantize() for b in self.blocks])


def _phase2_wls(X, W, seeds, cfg: HPCConfig):
    n = X.shape[0]
    per_blk_clamp = block_clamp_values(X, cfg).reshape(n, 1)
    clipped = np.clip(X, -per_blk_clamp, per_blk_clamp).astype(np.float32)
    base_d = seeds["d"].astype(np.float64).copy()
    base_m = seeds["dmin"].astype(np.float64).copy()
    ls = seeds["ls"].copy()
    lm = seeds["lm"].copy()
    scales = seeds["scales"].astype(np.float64)
    mins = seeds["mins"].astype(np.float64)
    ww = np.ones_like(X, dtype=np.float64) if W is None else W.astype(np.float64)

    for _ in range(5):
        codes = codes_from_params_batch(clipped, base_d, base_m, ls, lm).astype(np.float64)
        A = np.repeat(ls.astype(np.float64), 16, axis=1) * codes
        B = np.repeat(lm.astype(np.float64), 16, axis=1)
        Saa = np.sum(ww * A * A, axis=1)
        Sab = np.sum(ww * A * B, axis=1)
        Sbb = np.sum(ww * B * B, axis=1)
        Sxa = np.sum(ww * clipped.astype(np.float64) * A, axis=1)
        Sxb = np.sum(ww * clipped.astype(np.float64) * B, axis=1)
        det = Saa * Sbb - Sab * Sab
        valid = det > 1.0e-30
        safe_det = np.where(valid, det, 1.0)
        d_new = (Sbb * Sxa - Sab * Sxb) / safe_det
        m_new = (Sab * Sxa - Saa * Sxb) / safe_det
        upd_d = valid & (d_new > 0.0) & np.isfinite(d_new)
        upd_m = valid & (m_new > 0.0) & np.isfinite(m_new)
        base_d = np.where(upd_d, round_fp16(d_new.astype(np.float32)).astype(np.float64), base_d)
        base_m = np.where(upd_m, round_fp16(m_new.astype(np.float32)).astype(np.float64), base_m)

        safe_d = np.where(base_d > 1.0e-15, base_d, 1.0)
        safe_m = np.where(base_m > 1.0e-15, base_m, 1.0)
        ls = np.where(
            base_d[:, None] > 1.0e-15,
            np.clip(nearest_int(scales / safe_d[:, None]), 0, 15),
            0,
        ).astype(np.uint8)
        lm = np.where(
            base_m[:, None] > 1.0e-15,
            np.clip(nearest_int(mins / safe_m[:, None]), 0, 15),
            0,
        ).astype(np.uint8)

    return base_d.astype(np.float32), base_m.astype(np.float32)


def _bin_geometry():
    di = np.arange(TOTAL_CANDIDATES) // N_CAND_M
    mi = np.arange(TOTAL_CANDIDATES) % N_CAND_M
    return CAND_TO_QUHIT[di], CAND_TO_QUHIT[mi]


def _sieve_marginals(candidate_errors, graph_blocks, stride, temperature, cfg):
    n_blocks = candidate_errors.shape[0]
    pad = graph_blocks * stride - n_blocks
    ce = candidate_errors.astype(np.float64)
    if pad > 0:
        ce = np.concatenate([ce, np.full((pad, TOTAL_CANDIDATES), np.inf, dtype=np.float64)], axis=0)
    grouped = ce.reshape(graph_blocks, stride, TOTAL_CANDIDATES)
    finite = np.isfinite(grouped)
    counts = np.sum(finite, axis=1)  # (graph_blocks, 576)
    valid = counts > 0
    sums = np.sum(np.where(finite, grouped, 0.0), axis=1)
    agg = np.where(valid, sums / np.maximum(counts, 1), np.inf)
    mn = np.min(agg, axis=1, keepdims=True)
    mn = np.where(np.isfinite(mn), mn, 0.0)
    expo = np.where(valid, (agg - mn) / (2.0 * max(temperature, 1.0e-12)), np.inf)
    coeff = np.exp(-expo).reshape(graph_blocks, 6, 4, 6, 4)

    coarse = np.sum(coeff, axis=(2, 3, 4))  # (graph_blocks, 6)
    fine = np.sum(coeff, axis=(1, 2, 4))    # (graph_blocks, 6)
    cn = np.linalg.norm(coarse, axis=1, keepdims=True)
    fn = np.linalg.norm(fine, axis=1, keepdims=True)
    coarse = np.where(cn > 1.0e-30, coarse / np.maximum(cn, 1.0e-30), 0.0)
    fine = np.where(fn > 1.0e-30, fine / np.maximum(fn, 1.0e-30), 0.0)

    amps = np.zeros((2 * graph_blocks, 6), dtype=np.float64)
    amps[0::2] = coarse
    amps[1::2] = fine
    marg, _ = sieve_measure_chain(
        amps,
        block_chain_edges(graph_blocks),
        same_penalty=cfg.same_penalty,
        log_slack=cfg.log_slack,
        deterministic=True,
    )
    return marg[0::2], marg[1::2]


def _phase3_select(candidate_errors, cfg):
    n_blocks = candidate_errors.shape[0]
    if cfg.optimizer != "hpc" or n_blocks < 2:
        best = np.argmin(candidate_errors, axis=1).astype(np.int64)
        return best, 0.0, np.zeros(n_blocks, dtype=np.int64)

    stride = max(1, ceil(n_blocks / cfg.graph_max_blocks))
    graph_blocks = ceil(n_blocks / stride)
    temperature = robust_temperature(candidate_errors, cfg)
    coarse_marg, fine_marg = _sieve_marginals(
        candidate_errors, graph_blocks, stride, temperature, cfg
    )
    best, path = viterbi_select(
        candidate_errors,
        coarse_marg,
        fine_marg,
        temperature,
        stride,
        graph_blocks,
        cfg,
    )
    return best, temperature, path


def _compute_dc_carry(X, seeds, best, base_d, base_m, cfg, row_width):
    n = X.shape[0]
    carry = np.zeros(n, dtype=np.float32)
    blocks_per_row = row_width // QK_K if row_width and row_width % QK_K == 0 else 0
    rolling = 0.0
    for i in range(n):
        if blocks_per_row > 0 and i % blocks_per_row == 0:
            rolling = 0.0
        d16, m16 = candidate_pair(base_d[i], base_m[i], best[i])
        d = float(from_fp16_bits(d16))
        m = float(from_fp16_bits(m16))
        ls, lm = derive_subscales(seeds["scales"][i], seeds["mins"][i], d, m)
        codes = codes_from_params(X[i], d, m, ls, lm)
        xh = dequantize_params(d, m, ls, lm, codes)
        carry[i] = np.float32(cfg.dc_decay * rolling)
        dc_res = float(np.sum(X[i].astype(np.float64) - xh.astype(np.float64)))
        rolling = carry[i] + dc_res if cfg.carry_cumulative else dc_res
    return carry


def _per_sub_top_states(x, w, d, m, k=6):
    k = max(1, min(int(k), 6))
    xb = np.asarray(x, dtype=np.float32).reshape(NS, 16)
    if w is None:
        wb = np.ones((NS, 16), dtype=np.float32)
    else:
        wb = np.asarray(w, dtype=np.float32).reshape(NS, 16)
    ls_opts = np.arange(16, dtype=np.float32)[:, None]
    lm_opts = np.arange(16, dtype=np.float32)[None, :]
    d_sub = np.float32(d) * ls_opts
    m_sub = np.float32(m) * lm_opts
    safe = d_sub >= np.float32(1.0e-15)
    safe_d = np.where(safe, d_sub, np.float32(1.0))
    subs = xb[:, None, None, :]
    raw = (subs + m_sub[None, :, :, None]) / safe_d[None, :, :, None]
    q = np.clip(nearest_int(raw), 0, 3).astype(np.float32)
    q = np.where(safe[None, :, :, None], q, 0.0)
    deq = d_sub[None, :, :, None] * q - m_sub[None, :, :, None]
    err = np.sum(wb[:, None, None, :] * (subs - deq) ** 2, axis=3)
    flat = err.reshape(NS, 256)
    order = np.argsort(flat, axis=1, kind="stable")[:, :k]
    state_err = np.take_along_axis(flat, order, axis=1).astype(np.float64)
    state_ls = (order // 16).astype(np.uint8)
    state_lm = (order % 16).astype(np.uint8)
    return state_ls, state_lm, state_err


def _select_sub_states(state_ls, state_lm, state_err, cfg):
    if not cfg.subblock_sieve:
        return state_ls[:, 0].copy(), state_lm[:, 0].copy()
    amps = np.zeros((NS, 6), dtype=np.float64)
    for j in range(NS):
        err0 = state_err[j, 0]
        spread = float(state_err[j, 5] - state_err[j, 0])
        temp = spread * 0.3 if spread > 1.0e-15 else 0.1
        temp = max(temp, 1.0e-12)
        amp = np.exp(-(state_err[j] - err0) / temp)
        norm = float(np.linalg.norm(amp))
        amps[j] = amp / norm if norm > 1.0e-30 else 1.0 / np.sqrt(6.0)
    marg, _ = sieve_measure_chain(
        amps,
        subblock_chain_edges(NS),
        same_penalty=cfg.same_penalty,
        log_slack=cfg.log_slack,
        deterministic=True,
    )
    pick = np.argmax(marg, axis=1)
    ls = np.array([state_ls[j, pick[j]] for j in range(NS)], dtype=np.uint8)
    lm = np.array([state_lm[j, pick[j]] for j in range(NS)], dtype=np.uint8)
    return ls, lm


def _ls_refit(x, w, d, m, ls, lm, codes, max_d, max_m):
    x = np.asarray(x, dtype=np.float64)
    w = np.ones(QK_K, dtype=np.float64) if w is None else np.asarray(w, dtype=np.float64)
    A = np.repeat(np.asarray(ls, dtype=np.float64), 16) * np.asarray(codes, dtype=np.float64)
    B = np.repeat(np.asarray(lm, dtype=np.float64), 16)
    Saa = float(np.sum(w * A * A))
    Sab = float(np.sum(w * A * B))
    Sbb = float(np.sum(w * B * B))
    Sxa = float(np.sum(w * x * A))
    Sxb = float(np.sum(w * x * B))
    det = Saa * Sbb - Sab * Sab
    if det <= 1.0e-30:
        return float(d), float(m)
    d_new = (Sbb * Sxa - Sab * Sxb) / det
    m_new = (Sab * Sxa - Saa * Sxb) / det
    if d_new <= 0.0 or d_new >= 4.0 * (max_d + 1.0e-10):
        d_new = d
    if m_new <= 0.0 or m_new >= 4.0 * (max_m + 1.0e-10):
        m_new = m
    return float(round_fp16(np.float32(d_new))), float(round_fp16(np.float32(m_new)))


def _ulp_polish(x, w, d, m, ls, lm, radius):
    if radius <= 0:
        codes = codes_from_params(x, d, m, ls, lm)
        return float(d), float(m), codes, weighted_sse(x, w, d, m, ls, lm, codes)
    d16 = int(to_fp16_bits(np.float32(d)))
    m16 = int(to_fp16_bits(np.float32(m)))
    d_bits = np.arange(max(0, d16 - radius), min(0x7BFF, d16 + radius) + 1, dtype=np.uint16)
    m_bits = np.arange(max(0, m16 - radius), min(0x7BFF, m16 + radius) + 1, dtype=np.uint16)
    dd = from_fp16_bits(d_bits)
    mm = from_fp16_bits(m_bits)
    d_grid = np.repeat(dd, mm.size)
    m_grid = np.tile(mm, dd.size)
    ls_rep = np.repeat(np.asarray(ls, dtype=np.float32), 16)
    lm_rep = np.repeat(np.asarray(lm, dtype=np.float32), 16)
    d_sub = d_grid[:, None] * ls_rep[None, :]
    m_sub = m_grid[:, None] * lm_rep[None, :]
    safe = d_sub >= np.float32(1.0e-15)
    safe_d = np.where(safe, d_sub, np.float32(1.0))
    q = np.clip(nearest_int((x[None, :] + m_sub) / safe_d), 0, 3).astype(np.float32)
    q = np.where(safe, q, 0.0)
    deq = d_sub * q - m_sub
    ww = np.ones(QK_K, dtype=np.float64) if w is None else np.asarray(w, dtype=np.float64)
    err = np.sum(ww[None, :] * (np.asarray(x, dtype=np.float64)[None, :] - deq) ** 2, axis=1)
    k = int(np.argmin(err))
    codes = q[k].astype(np.uint8)
    return float(d_grid[k]), float(m_grid[k]), codes, float(err[k])


def _per_sub_scan(x, w, d, m):
    state_ls, state_lm, _ = _per_sub_top_states(x, w, d, m, k=1)
    return state_ls[:, 0], state_lm[:, 0]


def _assemble_block(x, w, seeds, base_d, base_m, cidx, dc_carry, cfg):
    d16, m16 = candidate_pair(base_d, base_m, cidx)
    d = float(from_fp16_bits(d16))
    m = float(from_fp16_bits(m16))
    ls, lm = derive_subscales(seeds["scales"], seeds["mins"], d, m)
    max_d, max_m = d, m
    prev = None
    for _ in range(5):
        s_ls, s_lm, s_err = _per_sub_top_states(x, w, d, m, cfg.subblock_states)
        ls, lm = _select_sub_states(s_ls, s_lm, s_err, cfg)
        codes = codes_from_params(x, d, m, ls, lm)
        d, m = _ls_refit(x, w, d, m, ls, lm, codes, max_d, max_m)
        cur = (int(to_fp16_bits(np.float32(d))), int(to_fp16_bits(np.float32(m))))
        if cur == prev:
            break
        prev = cur

    codes = codes_from_params(x, d, m, ls, lm)
    obj, sse = objective(x, w, d, m, ls, lm, codes, cfg, dc_carry)
    best = (obj, sse, d, m, ls.copy(), lm.copy(), codes.copy())

    ud, um, uc, _ = _ulp_polish(x, w, d, m, ls, lm, cfg.ulp_radius)
    uobj, usse = objective(x, w, ud, um, ls, lm, uc, cfg, dc_carry)
    if uobj < best[0] - 1.0e-15:
        best = (uobj, usse, ud, um, ls.copy(), lm.copy(), uc.copy())

    sls, slm = _per_sub_scan(x, w, ud, um)
    scodes = codes_from_params(x, ud, um, sls, slm)
    sobj, ssse = objective(x, w, ud, um, sls, slm, scodes, cfg, dc_carry)
    if sobj < best[0] - 1.0e-15:
        best = (sobj, ssse, ud, um, sls.copy(), slm.copy(), scodes.copy())

    _, _, bd, bm, bls, blm, bc = best
    refined = refine_codes_hadamard(x, w, bd, bm, bls, blm, bc, cfg, dc_carry)
    robj, rsse = objective(x, w, bd, bm, bls, blm, refined, cfg, dc_carry)
    if robj < best[0] - 1.0e-15:
        best = (robj, rsse, bd, bm, bls.copy(), blm.copy(), refined.copy())

    _, sse, d, m, ls, lm, codes = best
    return d, m, ls, lm, codes, best[0], sse


def _batch_objective(
    X: np.ndarray,
    W_f64: np.ndarray,
    d: np.ndarray,
    m: np.ndarray,
    ls: np.ndarray,
    lm: np.ndarray,
    codes: np.ndarray,
    carry: np.ndarray,
    cfg: HPCConfig,
) -> tuple[np.ndarray, np.ndarray]:
    xh = dequantize_params_batch(d, m, ls, lm, codes).astype(np.float64)
    e = X.astype(np.float64) - xh
    sse = np.sum(W_f64 * e * e, axis=1)
    if not cfg.use_spectral or (cfg.dc_lambda == 0.0 and cfg.vw_lambda == 0.0):
        return sse, sse
    fw = fold_weights(QK_K, cfg)
    pen = np.zeros(X.shape[0], dtype=np.float64)
    src = e
    m_len = QK_K // 2
    lvl = 0
    while m_len >= 1:
        dst = src[:, :m_len] + src[:, m_len : 2 * m_len]
        if m_len == 1:
            dst = dst + carry[:, None].astype(np.float64)
        if fw[lvl] != 0.0:
            pen += fw[lvl] * np.sum(dst * dst, axis=1)
        src = dst
        m_len //= 2
        lvl += 1
    return sse + pen, sse


def _batch_extended_dm_solve_and_ulp(
    X_f64: np.ndarray,
    W_f64: np.ndarray,
    ls: np.ndarray,
    lm: np.ndarray,
    codes: np.ndarray,
    d_cur: np.ndarray,
    m_cur: np.ndarray,
    carry: np.ndarray,
    cfg: HPCConfig,
) -> tuple[np.ndarray, np.ndarray]:
    """Closed-form 2x2 Cramer solve + O(1) quadratic ULP polish on true weighted SSE."""
    N = X_f64.shape[0]
    A = np.repeat(ls.astype(np.float64), 16, axis=1) * codes.astype(np.float64)
    B = np.repeat(lm.astype(np.float64), 16, axis=1)
    Saa = np.sum(W_f64 * A * A, axis=1)
    Sab = np.sum(W_f64 * A * B, axis=1)
    Sbb = np.sum(W_f64 * B * B, axis=1)
    Sxa = np.sum(W_f64 * X_f64 * A, axis=1)
    Sxb = np.sum(W_f64 * X_f64 * B, axis=1)

    det = Saa * Sbb - Sab * Sab
    valid = det > 1.0e-30
    s_det = np.where(valid, det, 1.0)
    d_new = (Sbb * Sxa - Sab * Sxb) / s_det
    m_new = (Sab * Sxa - Saa * Sxb) / s_det
    d_opt = np.where(valid & (d_new > 0.0) & np.isfinite(d_new), d_new, d_cur)
    m_opt = np.where(valid & (m_new >= 0.0) & np.isfinite(m_new), m_new, m_cur)

    rad = max(int(cfg.ulp_radius), 1)
    deltas = np.arange(-rad, rad + 1, dtype=np.int32)
    d16_c = to_fp16_bits(d_opt.astype(np.float32)).astype(np.int32)
    m16_c = to_fp16_bits(m_opt.astype(np.float32)).astype(np.int32)
    d_bits = np.clip(d16_c[:, None] + deltas[None, :], 0, 0x7BFF).astype(np.uint16)
    m_bits = np.clip(m16_c[:, None] + deltas[None, :], 0, 0x7BFF).astype(np.uint16)
    dd = from_fp16_bits(d_bits).astype(np.float64)[:, :, None]
    mm = from_fp16_bits(m_bits).astype(np.float64)[:, None, :]

    q_form = (
        Saa[:, None, None] * (dd * dd)
        - 2.0 * Sab[:, None, None] * (dd * mm)
        + Sbb[:, None, None] * (mm * mm)
        - 2.0 * Sxa[:, None, None] * dd
        + 2.0 * Sxb[:, None, None] * mm
    ).reshape(N, -1)
    best_idx = np.argmin(q_form, axis=1)
    K = deltas.size
    rows = np.arange(N)
    return dd[rows, best_idx // K, 0].astype(np.float32), mm[rows, 0, best_idx % K].astype(np.float32)


def _batch_algebraic_refine_codes(
    X_f64: np.ndarray,
    W_f64: np.ndarray,
    d: np.ndarray,
    m: np.ndarray,
    ls: np.ndarray,
    lm: np.ndarray,
    codes: np.ndarray,
    carry: np.ndarray,
    cfg: HPCConfig,
) -> np.ndarray:
    """Closed-form 1D quadratic coordinate projection for Vesica + DC + weighted SSE."""
    N = X_f64.shape[0]
    out = codes.astype(np.int64).copy()
    lam_vw = (float(cfg.vw_lambda) / QK_K) if cfg.use_spectral else 0.0
    lam_dc = (float(cfg.dc_lambda) / QK_K) if cfg.use_spectral else 0.0
    if lam_vw == 0.0 and lam_dc == 0.0:
        return out.astype(np.uint8)

    d_sub = np.repeat(d.astype(np.float64)[:, None] * ls.astype(np.float64), 16, axis=1)
    m_sub = np.repeat(m.astype(np.float64)[:, None] * lm.astype(np.float64), 16, axis=1)
    active = d_sub >= 1.0e-15
    e = X_f64 - (d_sub * out - m_sub)
    sse_live = np.sum(W_f64 * e * e, axis=1)
    sse_cap = sse_live * (1.0 + cfg.sse_budget)
    half = QK_K // 2
    v = e[:, :half] + e[:, half:]
    dc = np.sum(e, axis=1) + carry.astype(np.float64)
    denom = (W_f64 + lam_vw + lam_dc) * (d_sub * d_sub)
    safe_den = np.where(active & (denom > 1.0e-30), denom, 1.0)

    v_full = np.concatenate([v, v], axis=1)
    grad = d_sub * (W_f64 * e + lam_vw * v_full + lam_dc * dc[:, None])
    dq = np.where(active, nearest_int((grad / safe_den).astype(np.float32)), 0)
    q_new = np.clip(out + dq, 0, 3)

    for b in range(N):
        changed = np.where(q_new[b] != out[b])[0]
        if changed.size == 0:
            continue
        xb, wb, dsb, msb = X_f64[b], W_f64[b], d_sub[b], m_sub[b]
        eb, vb, dcb, sseb, capb = e[b], v[b], float(dc[b]), float(sse_live[b]), float(sse_cap[b])
        e_cand = xb[changed] - (dsb[changed] * q_new[b, changed] - msb[changed])
        de_cand = e_cand - eb[changed]
        dsse_cand = wb[changed] * (e_cand * e_cand - eb[changed] * eb[changed])
        pi_cand = np.where(changed < half, changed, changed - half)
        v_old = vb[pi_cand]
        v_new = v_old + de_cand
        d_spec = lam_vw * (v_old * v_old - v_new * v_new) + lam_dc * (dcb * dcb - (dcb + de_cand) ** 2)
        order = changed[np.argsort(-(d_spec - dsse_cand))]
        for k in order:
            q_try = int(q_new[b, k])
            if q_try == int(out[b, k]):
                continue
            e_new = xb[k] - (dsb[k] * q_try - msb[k])
            de = e_new - eb[k]
            dsse = wb[k] * (e_new * e_new - eb[k] * eb[k])
            if sseb + dsse > capb:
                continue
            p = k if k < half else k - half
            v_np = vb[p] + de
            dc_n = dcb + de
            spec_gain = lam_vw * (vb[p] * vb[p] - v_np * v_np) + lam_dc * (dcb * dcb - dc_n * dc_n)
            if spec_gain > dsse + 1.0e-18:
                out[b, k] = q_try
                eb[k] = e_new
                vb[p] = v_np
                dcb = dc_n
                sseb += dsse
    return out.astype(np.uint8)


def _refine_trajectory_algebraic(
    X: np.ndarray,
    X_f64: np.ndarray,
    W_f64: np.ndarray,
    Xb: np.ndarray,
    Wb: np.ndarray,
    Sw: np.ndarray,
    Sx: np.ndarray,
    safe_Sw: np.ndarray,
    d0: np.ndarray,
    m0: np.ndarray,
    ls0: np.ndarray,
    lm0: np.ndarray,
    codes0: np.ndarray,
    carry: np.ndarray,
    cfg: HPCConfig,
):
    N = X.shape[0]
    best_d, best_m = d0.copy(), m0.copy()
    best_ls, best_lm = ls0.copy(), lm0.copy()
    best_codes = codes0.copy()
    best_obj, best_sse = _batch_objective(X, W_f64, best_d, best_m, best_ls, best_lm, best_codes, carry, cfg)
    d, m, ls, lm, codes = best_d.copy(), best_m.copy(), best_ls.copy(), best_lm.copy(), best_codes.copy()
    ls_deltas = np.array([-3, -2, -1, 0, 1, 2, 3], dtype=np.int64)
    lm_deltas = np.array([-1, 0, 1], dtype=np.int64)
    n_idx = np.arange(N)[:, None]
    s_idx = np.arange(NS)[None, :]

    for _ in range(cfg.refine_passes):
        d_new, m_new = _batch_extended_dm_solve_and_ulp(X_f64, W_f64, ls, lm, codes, d, m, carry, cfg)
        obj_dm, sse_dm = _batch_objective(X, W_f64, d_new, m_new, ls, lm, codes, carry, cfg)
        imp_dm = sse_dm < best_sse - 1.0e-15
        if np.any(imp_dm):
            best_obj = np.where(imp_dm, obj_dm, best_obj)
            best_sse = np.where(imp_dm, sse_dm, best_sse)
            best_d = np.where(imp_dm, d_new, best_d)
            best_m = np.where(imp_dm, m_new, best_m)
            best_ls = np.where(imp_dm[:, None], ls, best_ls)
            best_lm = np.where(imp_dm[:, None], lm, best_lm)
            best_codes = np.where(imp_dm[:, None], codes, best_codes)
        d, m = best_d.copy(), best_m.copy()

        codes_re = codes_from_params_batch(X, d, m, ls, lm)
        obj_re, sse_re = _batch_objective(X, W_f64, d, m, ls, lm, codes_re, carry, cfg)
        imp_re = sse_re < best_sse - 1.0e-15
        if np.any(imp_re):
            best_obj = np.where(imp_re, obj_re, best_obj)
            best_sse = np.where(imp_re, sse_re, best_sse)
            best_codes = np.where(imp_re[:, None], codes_re, best_codes)
        codes = best_codes.copy()

        q = codes.astype(np.float64).reshape(N, NS, 16)
        Sqq = np.sum(Wb * q * q, axis=2)
        Swq = np.sum(Wb * q, axis=2)
        Sqx = np.sum(Wb * q * Xb, axis=2)
        q_bar = Swq / safe_Sw
        Vqq = np.maximum(Sqq - Swq * q_bar, 0.0)
        Cqx = Sqx - Sx * q_bar
        s_star = np.where(Vqq > 1.0e-30, np.maximum(Cqx / np.maximum(Vqq, 1.0e-30), 0.0), d[:, None] * ls)
        sd = np.where(d[:, None] > 1.0e-15, d[:, None], 1.0)
        sm = np.where(m[:, None] > 1.0e-15, m[:, None], 1.0)
        ls_center = np.where(d[:, None] > 1.0e-15, np.clip(nearest_int((s_star / sd).astype(np.float32)), 0, 15), 0)

        c_ls_base = np.clip(ls_center[:, :, None] + ls_deltas[None, None, :], 0, 15).astype(np.float64)
        d_sub_base = d.astype(np.float64)[:, None, None] * c_ls_base
        t_opt_base = np.maximum(0.0, (d_sub_base * Swq[:, :, None] - Sx[:, :, None]) / safe_Sw[:, :, None])
        lm_center = np.where(
            m[:, None, None] > 1.0e-15,
            np.clip(nearest_int((t_opt_base / sm[:, :, None]).astype(np.float32)), 0, 15),
            0,
        )

        cand_ls = np.repeat(c_ls_base, 3, axis=2)
        cand_lm = np.clip(
            np.repeat(lm_center, 3, axis=2) + np.tile(lm_deltas, 7)[None, None, :], 0, 15
        ).astype(np.float64)

        d_sub_c = d.astype(np.float64)[:, None, None] * cand_ls
        m_sub_c = m.astype(np.float64)[:, None, None] * cand_lm
        safe_dc = d_sub_c >= 1.0e-15
        sd_c = np.where(safe_dc, d_sub_c, 1.0)
        q_c = np.where(
            safe_dc[:, :, :, None],
            np.clip(
                nearest_int(((Xb[:, :, None, :] + m_sub_c[:, :, :, None]) / sd_c[:, :, :, None]).astype(np.float32)),
                0,
                3,
            ),
            0,
        ).astype(np.float64)
        e_c = Xb[:, :, None, :] - (d_sub_c[:, :, :, None] * q_c - m_sub_c[:, :, :, None])
        err_c = np.sum(Wb[:, :, None, :] * e_c * e_c, axis=3)
        pick = np.argmin(err_c, axis=2)
        ls_try = cand_ls[n_idx, s_idx, pick].astype(np.uint8)
        lm_try = cand_lm[n_idx, s_idx, pick].astype(np.uint8)
        codes_try = codes_from_params_batch(X, d, m, ls_try, lm_try)
        d_try, m_try = _batch_extended_dm_solve_and_ulp(X_f64, W_f64, ls_try, lm_try, codes_try, d, m, carry, cfg)
        obj_try, sse_try = _batch_objective(X, W_f64, d_try, m_try, ls_try, lm_try, codes_try, carry, cfg)
        imp_sub = sse_try < best_sse - 1.0e-15
        if np.any(imp_sub):
            best_obj = np.where(imp_sub, obj_try, best_obj)
            best_sse = np.where(imp_sub, sse_try, best_sse)
            best_d = np.where(imp_sub, d_try, best_d)
            best_m = np.where(imp_sub, m_try, best_m)
            best_ls = np.where(imp_sub[:, None], ls_try, best_ls)
            best_lm = np.where(imp_sub[:, None], lm_try, best_lm)
            best_codes = np.where(imp_sub[:, None], codes_try, best_codes)
        d, m, ls, lm, codes = best_d.copy(), best_m.copy(), best_ls.copy(), best_lm.copy(), best_codes.copy()

    refined = _batch_algebraic_refine_codes(X_f64, W_f64, best_d, best_m, best_ls, best_lm, best_codes, carry, cfg)
    d_r, m_r = _batch_extended_dm_solve_and_ulp(X_f64, W_f64, best_ls, best_lm, refined, best_d, best_m, carry, cfg)
    obj_r, sse_r = _batch_objective(X, W_f64, d_r, m_r, best_ls, best_lm, refined, carry, cfg)
    imp_r = (sse_r <= best_sse * (1.0 + cfg.sse_budget)) & (obj_r < best_obj - 1.0e-15)
    if np.any(imp_r):
        best_obj = np.where(imp_r, obj_r, best_obj)
        best_sse = np.where(imp_r, sse_r, best_sse)
        best_d = np.where(imp_r, d_r, best_d)
        best_m = np.where(imp_r, m_r, best_m)
        best_codes = np.where(imp_r[:, None], refined, best_codes)

    return best_d, best_m, best_ls, best_lm, best_codes, best_obj, best_sse


def _phase4_algebraic_batch(
    X: np.ndarray,
    W: np.ndarray | None,
    scales_seed: np.ndarray,
    mins_seed: np.ndarray,
    base_d: np.ndarray,
    base_m: np.ndarray,
    best: np.ndarray,
    carry: np.ndarray,
    standalone: list[FactorResult],
    cfg: HPCConfig,
) -> tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray, np.ndarray, int, int]:
    """Batched algebraic Phase-4 solver across N blocks (replaces brute-force 16x16 & ULP grids)."""
    N = X.shape[0]
    X_f64 = X.astype(np.float64)
    W_f64 = np.ones_like(X_f64) if W is None else W.astype(np.float64)
    Xb = X_f64.reshape(N, NS, 16)
    Wb = W_f64.reshape(N, NS, 16)
    Sw = np.sum(Wb, axis=2)
    Sx = np.sum(Wb * Xb, axis=2)
    safe_Sw = np.maximum(Sw, 1.0e-30)

    di = best // N_CAND_M
    mi = best % N_CAND_M
    d_v = round_fp16(base_d * MULTS_D[di])
    m_v = round_fp16(base_m * MULTS_M[mi])
    sd_v = np.where(d_v[:, None] > 1.0e-15, d_v[:, None], 1.0)
    sm_v = np.where(m_v[:, None] > 1.0e-15, m_v[:, None], 1.0)
    ls_v = np.where(d_v[:, None] > 1.0e-15, np.clip(nearest_int(scales_seed / sd_v), 0, 15), 0).astype(np.uint8)
    lm_v = np.where(m_v[:, None] > 1.0e-15, np.clip(nearest_int(mins_seed / sm_v), 0, 15), 0).astype(np.uint8)
    codes_v = codes_from_params_batch(X, d_v, m_v, ls_v, lm_v)

    d1, m1, ls1, lm1, c1, _, sse1 = _refine_trajectory_algebraic(
        X, X_f64, W_f64, Xb, Wb, Sw, Sx, safe_Sw, d_v, m_v, ls_v, lm_v, codes_v, carry, cfg
    )
    cand_hits = 0
    fac_hits = 0

    if cfg.use_factor_floor:
        d_f = np.array([f.d for f in standalone], dtype=np.float32)
        m_f = np.array([f.dmin for f in standalone], dtype=np.float32)
        ls_f = np.stack([f.ls for f in standalone], axis=0)
        lm_f = np.stack([f.lm for f in standalone], axis=0)
        codes_f = np.stack([f.codes for f in standalone], axis=0)
        d2, m2, ls2, lm2, c2, _, sse2 = _refine_trajectory_algebraic(
            X, X_f64, W_f64, Xb, Wb, Sw, Sx, safe_Sw, d_f, m_f, ls_f, lm_f, codes_f, carry, cfg
        )
        take2 = sse2 < sse1 - 1.0e-15
        fac_hits = int(np.sum(take2))
        d1 = np.where(take2, d2, d1)
        m1 = np.where(take2, m2, m1)
        ls1 = np.where(take2[:, None], ls2, ls1)
        lm1 = np.where(take2[:, None], lm2, lm1)
        c1 = np.where(take2[:, None], c2, c1)

    return d1, m1, ls1, lm1, c1, cand_hits, fac_hits


def _apply_dc_nudge(X, W, blocks, cfg, row_width):
    n = X.shape[0]
    blocks_per_row = row_width // QK_K if row_width and row_width % QK_K == 0 else 0
    rolling = 0.0
    for i in range(n):
        if blocks_per_row > 0 and i % blocks_per_row == 0:
            rolling = 0.0
        block = blocks[i]
        carry = np.float32(cfg.dc_decay * rolling)
        d = float(block.d_float)
        m = float(block.dmin_float)
        ls, lm = block.unpack_scales()
        codes = unpack_codes(block.qs)
        w = None if W is None else W[i]
        codes = dc_nudge_codes(X[i], d, m, ls, lm, codes, w, float(carry), cfg)
        blocks[i] = Q2KBlock(
            scales=pack_scales(ls, lm),
            qs=pack_codes(codes),
            d=block.d,
            dmin=block.dmin,
        )
        xh = blocks[i].dequantize()
        dc_res = float(np.sum(X[i].astype(np.float64) - xh.astype(np.float64)))
        rolling = float(carry) + dc_res if cfg.carry_cumulative else dc_res
    return blocks


_MP_STATE: dict[str, object] = {}


def _resolve_workers(cfg: HPCConfig, n_blocks: int) -> int:
    if cfg.workers == 1 or n_blocks < 4:
        return 1
    if cfg.workers > 1:
        return min(int(cfg.workers), n_blocks)
    if n_blocks < 16:
        return 1
    cpu = os.cpu_count() or 1
    return min(cpu, n_blocks)


def _phase2b_one(i: int) -> tuple[np.ndarray, FactorResult]:
    X = _MP_STATE["X"]
    W = _MP_STATE["W"]
    seeds = _MP_STATE["seeds"]
    base_d = _MP_STATE["base_d"]
    base_m = _MP_STATE["base_m"]
    cfg = _MP_STATE["cfg"]
    wi = None if W is None else W[i]
    cand = factor_candidates(
        X[i],
        wi,
        seeds["scales"][i],
        seeds["mins"][i],
        base_d[i],
        base_m[i],
        cfg,
    )
    fac_res = factor_only_solve(X[i], wi, cfg)
    return cand, fac_res


def _phase4_one(args: tuple[int, int, float, FactorResult]) -> tuple[Q2KBlock, int, int, float]:
    i, best_i, carry_i, fac = args
    X = _MP_STATE["X"]
    W = _MP_STATE["W"]
    seeds = _MP_STATE["seeds"]
    base_d = _MP_STATE["base_d"]
    base_m = _MP_STATE["base_m"]
    cfg = _MP_STATE["cfg"]

    wi = None if W is None else W[i]
    d, m, ls, lm, codes, obj, sse = _assemble_block(
        X[i], wi, seeds, base_d[i], base_m[i], best_i, carry_i, cfg
    )
    cand_hit = 0
    fac_hit = 0

    if cfg.use_candidate_floor:
        cd, cm, cls, clm = _candidate_config(
            seeds["scales"][i], seeds["mins"][i], base_d[i], base_m[i], best_i
        )
        ccodes = codes_from_params(X[i], cd, cm, cls, clm)
        cobj, csse = objective(
            X[i], wi, cd, cm, cls, clm, ccodes, cfg, carry_i
        )
        if cobj < obj - 1.0e-15:
            d, m, ls, lm, codes, obj, sse = cd, cm, cls, clm, ccodes, cobj, csse
            cand_hit = 1

    if cfg.use_factor_floor:
        fcodes = (
            refine_codes_hadamard(
                X[i], wi, fac.d, fac.dmin, fac.ls, fac.lm, fac.codes, cfg, carry_i
            )
            if carry_i != 0.0
            else fac.codes
        )
        fobj, fsse = (
            objective(X[i], wi, fac.d, fac.dmin, fac.ls, fac.lm, fcodes, cfg, carry_i)
            if carry_i != 0.0
            else (fac.objective, fac.sse)
        )
        if fobj < obj - 1.0e-15:
            d = float(fac.d)
            m = float(fac.dmin)
            ls = fac.ls.copy()
            lm = fac.lm.copy()
            codes = fcodes.copy()
            obj, sse = fobj, fsse
            fac_hit = 1

    blk_obj = make_block(d, m, ls, lm, codes)
    return blk_obj, cand_hit, fac_hit, blk_obj.error(X[i])


class Q2KQuantizer:
    def __init__(self, config: HPCConfig | None = None):
        self.config = (config or HPCConfig()).validate()

    def quantize(
        self,
        weights: np.ndarray,
        importance: np.ndarray | None = None,
        row_width: int | None = None,
        status_callback=None,
        stop_event=None,
    ) -> QuantizedTensor:
        def _emit(phase: str, done: int, total: int, detail: str, **extra) -> None:
            if status_callback is not None:
                status_callback(
                    {
                        "phase": phase,
                        "done": done,
                        "total": total,
                        "detail": detail,
                        **extra,
                    }
                )

        def _check_stop() -> None:
            if stop_event is not None and stop_event.is_set():
                raise InterruptedError("Quantization cancelled by user")

        cfg = self.config
        x = np.asarray(weights, dtype=np.float32)
        if x.size == 0:
            raise ValueError("weight tensor is empty")
        if x.size % QK_K != 0:
            raise ValueError("weight count must be a multiple of 256")
        if x.ndim == 2 and row_width is None and x.shape[1] % QK_K == 0:
            row_width = int(x.shape[1])
        x = x.ravel()
        n_blocks = x.size // QK_K

        if cfg.device != "cpu":
            from .cuda_backend import cuda_is_available, quantize_cuda

            if cfg.device.startswith("cuda") or (
                cfg.device == "auto" and cfg.workers == 0 and n_blocks >= 32 and cuda_is_available()
            ):
                dev_str = "cuda" if cfg.device == "auto" else cfg.device
                res = quantize_cuda(
                    weights,
                    importance,
                    row_width,
                    cfg,
                    status_callback=status_callback,
                    stop_event=stop_event,
                    device=dev_str,
                )
                if cfg.verbose:
                    _report(res.stats)
                return res

        X = x.reshape(n_blocks, QK_K)

        if importance is not None:
            imp = np.asarray(importance, dtype=np.float32).ravel()
            if imp.size != x.size:
                raise ValueError("importance must match the weight count")
            if np.any(imp < 0.0) or not np.all(np.isfinite(imp)):
                raise ValueError("importance must be finite and non-negative")
            W_raw = imp.reshape(n_blocks, QK_K)
            if cfg.temper_imatrix:
                sig2 = np.mean(X.astype(np.float64) ** 2, axis=1, keepdims=True)
                W = (
                    np.sqrt(np.maximum(W_raw.astype(np.float64), 1.0e-6))
                    * np.sqrt(sig2 + X.astype(np.float64) ** 2)
                )
                w_mean = np.mean(W, axis=1, keepdims=True)
                W = np.where(w_mean > 1.0e-30, W / np.maximum(w_mean, 1.0e-30), 1.0).astype(np.float32)
            else:
                W = W_raw
        else:
            W = None

        sigma = float(np.sqrt(np.mean(x.astype(np.float64) ** 2)))
        _check_stop()
        clamp_val = seed_clamp_value(x, cfg)
        _emit(
            "Phase 1: Kurtosis Clamp & Batched GGML Seeds",
            0,
            n_blocks,
            f"blocks={n_blocks} sigma={sigma:.5f} clamp={clamp_val:.5f} imatrix={'yes' if W is not None else 'no'}",
            sigma=sigma,
        )
        seeds = build_seeds(X, W, cfg, clamp_val)
        _check_stop()
        _emit(
            "Phase 2a: Vectorized Superblock WLS",
            0,
            n_blocks,
            f"Solving 5-iteration WLS across {n_blocks} superblocks",
            sigma=sigma,
        )
        base_d, base_m = _phase2_wls(X, W, seeds, cfg)

        candidate_errors = np.full((n_blocks, TOTAL_CANDIDATES), np.inf, dtype=np.float32)
        standalone: list[FactorResult] = []
        t_cand = time.time()
        last_emit = 0.0
        step_report = max(1, min(32, n_blocks // 20 or 1))
        n_workers = _resolve_workers(cfg, n_blocks)
        _MP_STATE.update(
            {
                "X": X,
                "W": W,
                "seeds": seeds,
                "base_d": base_d,
                "base_m": base_m,
                "cfg": cfg,
            }
        )

        blocks: list[Q2KBlock] = []
        factor_floor_used = 0
        candidate_floor_used = 0
        running_sse = 0.0

        if n_workers > 1 and "fork" in mp.get_all_start_methods():
            ctx = mp.get_context("fork")
            chunksize = max(1, min(16, n_blocks // (n_workers * 4) or 1))
            pool = ctx.Pool(processes=n_workers)
            try:
                for i, (cand_row, fac_res) in enumerate(
                    pool.imap(_phase2b_one, range(n_blocks), chunksize=chunksize)
                ):
                    _check_stop()
                    candidate_errors[i] = cand_row
                    standalone.append(fac_res)
                    now = time.time()
                    if (i + 1) % step_report == 0 or (i + 1) == n_blocks or (now - last_emit) >= 0.25:
                        last_emit = now
                        elapsed = max(now - t_cand, 1.0e-6)
                        rate = (i + 1) / elapsed
                        eta = (n_blocks - (i + 1)) / max(rate, 1.0e-9)
                        _emit(
                            f"Phase 2b: Analog-Guided Factored Field ({n_workers} workers)",
                            i + 1,
                            n_blocks,
                            f"blk {i+1}/{n_blocks} ({rate:.1f} blk/s, ETA {eta:.1f}s) "
                            f"d={float(fac_res.d):.5f} dmin={float(fac_res.dmin):.5f} "
                            f"obj={fac_res.objective:.5e} starts={fac_res.starts}",
                            rate=rate,
                            eta=eta,
                            sigma=sigma,
                        )
                pool.close()
                pool.join()
            except BaseException:
                pool.terminate()
                pool.join()
                raise
        else:
            for i in range(n_blocks):
                _check_stop()
                cand_row, fac_res = _phase2b_one(i)
                candidate_errors[i] = cand_row
                standalone.append(fac_res)
                now = time.time()
                if (i + 1) % step_report == 0 or (i + 1) == n_blocks or (now - last_emit) >= 0.25:
                    last_emit = now
                    elapsed = max(now - t_cand, 1.0e-6)
                    rate = (i + 1) / elapsed
                    eta = (n_blocks - (i + 1)) / max(rate, 1.0e-9)
                    _emit(
                        "Phase 2b: Analog-Guided Factored Candidate Field",
                        i + 1,
                        n_blocks,
                        f"blk {i+1}/{n_blocks} ({rate:.1f} blk/s, ETA {eta:.1f}s) "
                        f"d={float(fac_res.d):.5f} dmin={float(fac_res.dmin):.5f} "
                        f"obj={fac_res.objective:.5e} starts={fac_res.starts}",
                        rate=rate,
                        eta=eta,
                        sigma=sigma,
                    )

        _MP_STATE.clear()
        _check_stop()
        _emit(
            "Phase 3: 6-State Sieve & 36-State Viterbi DP",
            0,
            n_blocks,
            f"Running Sieve + 36-state Viterbi sequence optimization ({cfg.optimizer.upper()})",
            sigma=sigma,
        )
        best, temperature, _ = _phase3_select(candidate_errors, cfg)
        carry = _compute_dc_carry(X, seeds, best, base_d, base_m, cfg, row_width)
        _emit(
            "Phase 3.9: Viterbi Path & Rolling DC Carry",
            n_blocks,
            n_blocks,
            f"Boltzmann temp={temperature:.4e}, max |DC carry|={float(np.max(np.abs(carry))):.4e}",
            temperature=temperature,
            sigma=sigma,
        )

        t_asm = time.time()
        batch_sz = 256
        for start in range(0, n_blocks, batch_sz):
            _check_stop()
            stop = min(start + batch_sz, n_blocks)
            W_chunk = None if W is None else W[start:stop]
            d_b, m_b, ls_b, lm_b, codes_b, c_hits, f_hits = _phase4_algebraic_batch(
                X[start:stop],
                W_chunk,
                seeds["scales"][start:stop],
                seeds["mins"][start:stop],
                base_d[start:stop],
                base_m[start:stop],
                best[start:stop],
                carry[start:stop],
                standalone[start:stop],
                cfg,
            )
            candidate_floor_used += c_hits
            factor_floor_used += f_hits
            for k in range(stop - start):
                blk_obj = make_block(d_b[k], m_b[k], ls_b[k], lm_b[k], codes_b[k])
                blocks.append(blk_obj)
                running_sse += blk_obj.error(X[start + k])

            now = time.time()
            elapsed = max(now - t_asm, 1.0e-6)
            rate = stop / elapsed
            eta = (n_blocks - stop) / max(rate, 1.0e-9)
            cur_rmse = float(np.sqrt(running_sse / (stop * QK_K)))
            _emit(
                "Phase 4: Algebraic Coupled Bilinear Assembly",
                stop,
                n_blocks,
                f"blk {stop}/{n_blocks} ({rate:.1f} blk/s, ETA {eta:.1f}s) "
                f"rmse={cur_rmse:.6e} rmse/sigma={cur_rmse/max(sigma, 1e-15):.4f} "
                f"floors(cand={candidate_floor_used}, fac={factor_floor_used})",
                rmse=cur_rmse,
                sigma=sigma,
                temperature=temperature,
                cand_floors=candidate_floor_used,
                fac_floors=factor_floor_used,
                rate=rate,
                eta=eta,
            )

        therm_improved = 0
        if cfg.therm_passes > 0 and n_blocks > 0:
            _check_stop()
            t_therm = time.time()
            _emit(
                "Phase 4.5: Thermal Refinery (Pair Heat-Bath)",
                0,
                n_blocks,
                f"annealing {n_blocks} blocks: passes={cfg.therm_passes} "
                f"sweeps={cfg.therm_sweeps} T0={cfg.therm_t0} decay={cfg.therm_t_decay} "
                f"seed={cfg.therm_seed}",
                sigma=sigma,
                temperature=temperature,
            )
            therm_d = np.empty(n_blocks, dtype=np.float64)
            therm_m = np.empty(n_blocks, dtype=np.float64)
            therm_ls = np.empty((n_blocks, NS), dtype=np.uint8)
            therm_lm = np.empty((n_blocks, NS), dtype=np.uint8)
            therm_codes = np.empty((n_blocks, QK_K), dtype=np.uint8)
            for i, b in enumerate(blocks):
                therm_d[i] = b.d_float
                therm_m[i] = b.dmin_float
                therm_ls[i], therm_lm[i] = b.unpack_scales()
                therm_codes[i] = unpack_codes(b.qs)
            last_therm = [0.0, 0]

            def _therm_progress(done, total, improved):
                now = time.time()
                if (now - last_therm[0]) >= 0.25 or done == total:
                    last_therm[0] = now
                    _emit(
                        "Phase 4.5: Thermal Refinery (Pair Heat-Bath)",
                        done,
                        total,
                        f"blk {done}/{total} ({max(done, 1)/max(now - t_therm, 1.0e-6):.1f} blk/s) "
                        f"improved={improved}",
                        sigma=sigma,
                        temperature=temperature,
                    )

            therm_d, therm_m, therm_ls, therm_lm, therm_codes, therm_improved = thermal_refine_tensor(
                X,
                None if W is None else W,
                therm_d,
                therm_m,
                therm_ls,
                therm_lm,
                therm_codes,
                carry,
                cfg,
                dm_solve=_batch_extended_dm_solve_and_ulp,
                progress=_therm_progress,
            )
            blocks = [
                make_block(therm_d[i], therm_m[i], therm_ls[i], therm_lm[i], therm_codes[i])
                for i in range(n_blocks)
            ]
            _emit(
                "Phase 4.5: Thermal Refinery (Pair Heat-Bath)",
                n_blocks,
                n_blocks,
                f"done in {time.time() - t_therm:.1f}s, blocks improved={therm_improved}/{n_blocks}",
                sigma=sigma,
                temperature=temperature,
            )

        if cfg.pin_dc and n_blocks > 0:
            _check_stop()
            t_pin = time.time()
            _emit(
                "Phase 4.7: Zero-DC Pin (Q2_K Free Lunch)",
                0,
                n_blocks,
                "re-solving (d, m) on the exact dc=0 constraint line "
                "(exact-JS zero-coherent-residual pin, SSE-nondecreasing)",
                sigma=sigma,
                temperature=temperature,
            )
            pin_d = np.empty(n_blocks, dtype=np.float64)
            pin_m = np.empty(n_blocks, dtype=np.float64)
            pin_ls = np.empty((n_blocks, NS), dtype=np.uint8)
            pin_lm = np.empty((n_blocks, NS), dtype=np.uint8)
            pin_codes = np.empty((n_blocks, QK_K), dtype=np.uint8)
            for i, b in enumerate(blocks):
                pin_d[i] = b.d_float
                pin_m[i] = b.dmin_float
                pin_ls[i], pin_lm[i] = b.unpack_scales()
                pin_codes[i] = unpack_codes(b.qs)
            pin_d, pin_m = pin_q2k_dc_residual(
                pin_d, pin_m, pin_ls, pin_lm, pin_codes, X.astype(np.float64)
            )
            blocks = [
                make_block(pin_d[i], pin_m[i], pin_ls[i], pin_lm[i], pin_codes[i])
                for i in range(n_blocks)
            ]
            _emit(
                "Phase 4.7: Zero-DC Pin (Q2_K Free Lunch)",
                n_blocks,
                n_blocks,
                f"done in {time.time() - t_pin:.1f}s",
                sigma=sigma,
                temperature=temperature,
            )

        if cfg.apply_dc_carry and (cfg.dc_lambda > 0.0 or cfg.dc_decay > 0.0):
            _check_stop()
            _emit(
                "Phase 4.8: Sequential Row-Aware DC Residual Nudge",
                n_blocks,
                n_blocks,
                f"Cancelling cumulative row DC residuals (row_width={row_width or QK_K})",
                sigma=sigma,
                temperature=temperature,
            )
            blocks = _apply_dc_nudge(X, W, blocks, cfg, row_width)

        total_sse = 0.0
        weighted = 0.0
        for i, b in enumerate(blocks):
            e = X[i].astype(np.float64) - b.dequantize().astype(np.float64)
            total_sse += float(np.dot(e, e))
            if W is None:
                weighted += float(np.dot(e, e))
            else:
                weighted += float(np.dot(W[i].astype(np.float64), e * e))

        rmse = float(np.sqrt(total_sse / x.size))
        stats = TensorStats(
            n_blocks=n_blocks,
            total_sse=total_sse,
            weighted_sse=weighted,
            rmse=rmse,
            sigma=sigma,
            rmse_over_sigma=rmse / sigma if sigma > 1.0e-15 else 0.0,
            temperature=temperature,
            factor_floor_used=factor_floor_used,
            candidate_floor_used=candidate_floor_used,
            therm_improved=therm_improved,
        )
        _emit(
            "Phase 5: Tensor Complete",
            n_blocks,
            n_blocks,
            f"Done: blocks={n_blocks} rmse={rmse:.6e} rmse/sigma={stats.rmse_over_sigma:.5f} "
            f"wSSE={weighted:.5e} temp={temperature:.3e} "
            f"floors(cand={candidate_floor_used}, fac={factor_floor_used})",
            rmse=rmse,
            sigma=sigma,
            temperature=temperature,
            cand_floors=candidate_floor_used,
            fac_floors=factor_floor_used,
            therm_improved=therm_improved,
        )
        scales, qs, dm = _stack_blocks(blocks)
        factor_objectives = np.array([r.objective for r in standalone], dtype=np.float64)
        result = QuantizedTensor(
            blocks=blocks,
            scales=scales,
            qs=qs,
            dm=dm,
            best_candidate=best,
            factor_objectives=factor_objectives,
            config=cfg,
            stats=stats,
        )
        if cfg.verbose:
            _report(stats)
        return result


def _stack_blocks(blocks):
    n = len(blocks)
    scales = np.empty((n, NS), dtype=np.uint8)
    qs = np.empty((n, QK_K // 4), dtype=np.uint8)
    dm = np.empty((n, 2), dtype=np.uint16)
    for i, b in enumerate(blocks):
        scales[i] = b.scales
        qs[i] = b.qs
        dm[i, 0] = b.d
        dm[i, 1] = b.dmin
    return scales, qs, dm


def _report(stats: TensorStats) -> None:
    extra = f" therm={stats.therm_improved}" if stats.therm_improved else ""
    print(
        f"Q2_K V2: blocks={stats.n_blocks} rmse={stats.rmse:.6e} "
        f"rmse/sigma={stats.rmse_over_sigma:.5f} temp={stats.temperature:.3e} "
        f"floors(cand={stats.candidate_floor_used}, factor={stats.factor_floor_used}){extra}"
    )