Function sam3_cxblock_forward

sam3.cpp:9066–9107

CXBlock: depthwise conv + LayerNorm + pointwise MLP with residual scaling.

// CXBlock: depthwise conv + LayerNorm + pointwise MLP with residual scaling.
static struct ggml_tensor* sam3_cxblock_forward(
    struct ggml_context* ctx,
    struct ggml_tensor* x,       // [D, H, W, B]
    struct ggml_tensor* dw_w,    // [7, 7, 1, D] depthwise
    struct ggml_tensor* dw_b,    // [D]
    struct ggml_tensor* norm_w,  // [D]
    struct ggml_tensor* norm_b,  // [D]
    struct ggml_tensor* fc1_w,   // [D, 1024]
    struct ggml_tensor* fc1_b,   // [1024]
    struct ggml_tensor* fc2_w,   // [1024, D]
    struct ggml_tensor* fc2_b,   // [D]
    struct ggml_tensor* gamma)   // [D]
{
    const int D = (int)x->ne[0];
    const int H = (int)x->ne[1];
    const int W = (int)x->ne[2];

    // ggml conv expects WHCB layout; internal feature maps are stored as CWHB.
    auto* x_whcb = ggml_cont(ctx, ggml_permute(ctx, x, 2, 0, 1, 3));

    // Depthwise conv (groups = D): use the direct depthwise path.
    // ggml_conv_2d_dw_direct only supports f32 kernel — cast if needed.
    auto* dw_w_f32 = (dw_w->type == GGML_TYPE_F32) ? dw_w : ggml_cast(ctx, dw_w, GGML_TYPE_F32);
    auto* h = ggml_conv_2d_dw_direct(ctx, dw_w_f32, x_whcb, 1, 1, 3, 3, 1, 1);
    h = ggml_add(ctx, h, ggml_reshape_4d(ctx, dw_b, 1, 1, D, 1));
    h = ggml_cont(ctx, ggml_permute(ctx, h, 1, 2, 0, 3));

    // LayerNorm2d
    h = sam3_layer_norm_2d(ctx, h, norm_w, norm_b);

    // Pointwise MLP: reshape to [D, H*W, B], apply FC, reshape back
    auto* flat = ggml_reshape_3d(ctx, h, D, H * W, 1);
    flat = ggml_add(ctx, ggml_mul_mat(ctx, fc1_w, flat), fc1_b);
    flat = ggml_gelu(ctx, flat);
    flat = ggml_add(ctx, ggml_mul_mat(ctx, fc2_w, flat), fc2_b);
    h = ggml_reshape_4d(ctx, flat, D, H, W, 1);

    // Residual with learnable scaling: x + gamma * h
    auto* gamma_4d = ggml_reshape_4d(ctx, gamma, D, 1, 1, 1);
    h = ggml_mul(ctx, h, gamma_4d);
    return ggml_add(ctx, x, h);
}

/*****************************************************************************
** Prompt building for memory attention (Phase 7)