feat(EX): Algorithm Factor Replacement Engine — dlopen-based CUDA kernel dispatch

Factors: 0 (moe_topk_softmax), 2 (moe_fused_gemm), 5 (gdn_chunk_fwd)
Fixes: topk_softmax fallback (2304x/token), GDN NaN (frac=0.9998-1.0)

ex_engine/build.sh

@@ -0,0 +1,161 @@
+#!/bin/bash
+# ex_engine/build.sh — Compile EX Engine factor .so libraries
+#
+# CCCL parallel: ci/build_cub.sh selects compiler, arch, std
+# We select compiler (corex clang or nvcc), arch (SM70), build .so
+#
+# Usage:
+#   ./ex_engine/build.sh              # auto-detect toolchain
+#   ./ex_engine/build.sh --nvcc       # force nvcc
+#   ./ex_engine/build.sh --corex      # force corex clang
+#
+# Output: ex_engine/build/ex_factor_N.so for each factor
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+BUILD_DIR="${SCRIPT_DIR}/build"
+CSRC_DIR="${SCRIPT_DIR}/csrc"
+INCLUDE_DIR="${SCRIPT_DIR}/include"
+
+mkdir -p "$BUILD_DIR"
+
+# ============================================================================
+# Toolchain detection (CCCL pattern: .devcontainer/launch.sh --host)
+# ============================================================================
+
+COREX_ROOT="/usr/local/corex"
+COREX_CLANG="${COREX_ROOT}/lib64/clang/16"
+NVCC="nvcc"
+COMPILER=""
+
+detect_toolchain() {
+    if [[ "${1:-auto}" == "--corex" ]] || [[ -d "$COREX_CLANG" && "${1:-auto}" != "--nvcc" ]]; then
+        # BI-V100 corex SDK — use clang/16 as CUDA compiler
+        COMPILER="corex"
+        echo "[EX] Using corex clang/16 toolchain at ${COREX_ROOT}"
+    elif command -v nvcc &>/dev/null; then
+        COMPILER="nvcc"
+        echo "[EX] Using nvcc toolchain"
+    else
+        echo "[EX] ERROR: No CUDA compiler found"
+        exit 1
+    fi
+}
+
+# ============================================================================
+# Compile a single factor .cu → .so
+# ============================================================================
+
+compile_factor() {
+    local factor_id=$1
+    local cu_file=$2
+    local so_name="ex_factor_${factor_id}.so"
+    local so_path="${BUILD_DIR}/${so_name}"
+
+    echo "[EX] Compiling factor ${factor_id}: $(basename ${cu_file}) → ${so_name}"
+
+    if [[ "$COMPILER" == "corex" ]]; then
+        # CoreX/Iluvatar: clang-based CUDA compilation
+        # SM70 = BI-V100 architecture
+        "${COREX_ROOT}/bin/clang++" \
+            -x cuda \
+            --cuda-gpu-arch=sm_70 \
+            -std=c++17 \
+            -O2 \
+            -shared -fPIC \
+            -I"${INCLUDE_DIR}" \
+            -I"${COREX_ROOT}/include" \
+            -L"${COREX_ROOT}/lib64" \
+            -lcudart \
+            -o "${so_path}" \
+            "${cu_file}"
+    else
+        # Standard nvcc
+        nvcc \
+            -arch=sm_70 \
+            -std=c++17 \
+            -O2 \
+            --compiler-options '-fPIC' \
+            -shared \
+            -I"${INCLUDE_DIR}" \
+            -o "${so_path}" \
+            "${cu_file}"
+    fi
+
+    if [[ -f "${so_path}" ]]; then
+        local size=$(stat -c%s "${so_path}" 2>/dev/null || stat -f%z "${so_path}" 2>/dev/null)
+        echo "[EX] ✓ ${so_name} (${size} bytes)"
+    else
+        echo "[EX] ✗ FAILED: ${so_name}"
+        return 1
+    fi
+}
+
+# ============================================================================
+# Compile the registry shared library
+# ============================================================================
+
+compile_registry() {
+    local so_path="${BUILD_DIR}/libex_registry.so"
+    echo "[EX] Compiling registry → libex_registry.so"
+
+    gcc -O2 -shared -fPIC \
+        -I"${INCLUDE_DIR}" \
+        -o "${so_path}" \
+        "${CSRC_DIR}/ex_registry.c" \
+        -ldl
+
+    if [[ -f "${so_path}" ]]; then
+        echo "[EX] ✓ libex_registry.so"
+    else
+        echo "[EX] ✗ FAILED: libex_registry.so"
+        return 1
+    fi
+}
+
+# ============================================================================
+# Main
+# ============================================================================
+
+detect_toolchain "${1:-auto}"
+
+echo ""
+echo "========================================"
+echo "  EX Engine Build"
+echo "  Toolchain: ${COMPILER}"
+echo "  Output: ${BUILD_DIR}/"
+echo "========================================"
+echo ""
+
+# Build registry first
+compile_registry
+
+# Factor mapping (must match ex_engine.h factor IDs)
+FACTORS=(
+    "0:factor_moe_topk_softmax.cu"
+    "2:factor_moe_fused_gemm.cu"
+    "5:factor_gdn_chunk_fwd.cu"
+)
+
+TOTAL=0
+SUCCESS=0
+for entry in "${FACTORS[@]}"; do
+    fid="${entry%%:*}"
+    cu_file="${CSRC_DIR}/${entry##*:}"
+    TOTAL=$((TOTAL + 1))
+    if [[ -f "$cu_file" ]]; then
+        if compile_factor "$fid" "$cu_file"; then
+            SUCCESS=$((SUCCESS + 1))
+        fi
+    else
+        echo "[EX] SKIP factor ${fid}: ${cu_file} not found"
+    fi
+done
+
+echo ""
+echo "========================================"
+echo "  Build complete: ${SUCCESS}/${TOTAL} factors"
+echo "  Output: ${BUILD_DIR}/"
+echo "========================================"
+ls -la "${BUILD_DIR}/"