W18: context cleanup + CLI fixes + loader audit + CI matrix (W18.1-W18.4)

- W18.1 (王测+林深): Remove g_max_tokens dead API, UTF-8 bounds protection, deduplicate token counting, 0xC0/0xC1 handling, add 13 test blocks (36 checks)
- W18.2 (赵码+朱晴): Fix /context no-session error message, /status 3-state connection display
- W18.3 (曹武+徐磊): plugin_loader security audit — 9 dimensions, rating C, 1 HIGH + 2 MEDIUM findings
- W18.4 (马奔+胡桐): CI dual-platform matrix (Ubuntu clang-18 + Windows clang-cl), ccache, build timing baseline

Build 0 error, ctest 5/5 pass, metadata check clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -6,6 +6,11 @@ on:
   pull_request:
     branches: [master]
 
+env:
+  CMAKE_BUILD_PARALLEL_LEVEL: 0
+  CCACHE_DIR: ${{ github.workspace }}/.ccache
+  CCACHE_MAXSIZE: 256M
+
 jobs:
   # ── 动态矩阵 ──────────────────────────────────────────────
   # PR 仅跑 Ubuntu 节省 minutes；push master 跑全矩阵 Ubuntu + Windows
@@ -36,11 +41,48 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
+      # ── 1. 源码检出 ──────────────────────────────────────
       - name: Checkout
         uses: actions/checkout@v4
         with:
           fetch-depth: 1
 
+      # ── 2. 平台编译工具链 ─────────────────────────────────
+      # Ubuntu: clang-18 + Ninja + ccache
+      - name: Install toolchain (Ubuntu)
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y -qq clang-18 ninja-build ccache
+          echo "CC=clang-18" >> $GITHUB_ENV
+          echo "CXX=clang++-18" >> $GITHUB_ENV
+
+      # Windows: LLVM (clang-cl) + Ninja + ccache
+      - name: Install toolchain (Windows)
+        if: runner.os == 'Windows'
+        shell: bash
+        run: |
+          choco install -y llvm ninja ccache --no-progress 2>/dev/null || true
+          # Add clang-cl to PATH (both possible locations)
+          if [ -d "/c/Program Files/LLVM/bin" ]; then
+            echo "/c/Program Files/LLVM/bin" >> $GITHUB_PATH
+          elif [ -d "/c/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Tools/Llvm/x64/bin" ]; then
+            echo "/c/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Tools/Llvm/x64/bin" >> $GITHUB_PATH
+          fi
+          echo "CC=clang-cl" >> $GITHUB_ENV
+          echo "CXX=clang-cl" >> $GITHUB_ENV
+
+      # ── 3. ccache 缓存恢复 ────────────────────────────────
+      - name: Cache ccache
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.CCACHE_DIR }}
+          key: ${{ runner.os }}-ccache-${{ matrix.build_type }}-${{ github.run_id }}
+          restore-keys: |
+            ${{ runner.os }}-ccache-${{ matrix.build_type }}-
+            ${{ runner.os }}-ccache-
+
+      # ── 4. Python + Conan ─────────────────────────────────
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
@@ -49,6 +91,7 @@ jobs:
       - name: Install Conan
         run: pip install conan
 
+      # ── 5. Conan 依赖缓存 ─────────────────────────────────
       - name: Cache Conan
         uses: actions/cache@v4
         with:
@@ -60,16 +103,57 @@ jobs:
             ${{ runner.os }}-conan-${{ matrix.build_type }}-
             ${{ runner.os }}-conan-
 
+      # ── 6. Conan 依赖安装 ─────────────────────────────────
       - name: Install Conan dependencies
+        shell: bash
         run: |
           conan profile detect --force
           conan install deps --build=missing -s build_type=${{ matrix.build_type }}
 
+      # ── 7. CMake 配置 ─────────────────────────────────────
       - name: Configure CMake
-        run: cmake --preset conan-release
+        shell: bash
+        run: |
+          cmake --preset ci-release \
+            -DCMAKE_C_COMPILER_LAUNCHER=ccache \
+            -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
 
+      # ── 8. 构建（含计时） ─────────────────────────────────
       - name: Build
-        run: cmake --build --preset conan-release --config ${{ matrix.build_type }}
+        id: build
+        shell: bash
+        run: |
+          echo "::group::Build (${{ matrix.os }})"
+          START_NS=$(date +%s%N 2>/dev/null || echo 0)
+          START_S=$(date +%s)
+          cmake --build --preset ci-release --config ${{ matrix.build_type }}
+          END_S=$(date +%s)
+          END_NS=$(date +%s%N 2>/dev/null || echo 0)
+          DURATION=$((END_S - START_S))
+          echo "::endgroup::"
+          echo "duration=${DURATION}" >> $GITHUB_OUTPUT
+          echo "Build wall time: ${DURATION}s"
 
+      # ── 9. ccache 统计 ────────────────────────────────────
+      - name: ccache stats
+        if: always()
+        shell: bash
+        run: |
+          ccache -s || echo "ccache stats unavailable"
+          ccache -z || true
+
+      # ── 10. 测试 ──────────────────────────────────────────
       - name: Test
-        run: ctest --preset conan-release -C ${{ matrix.build_type }} --output-on-failure
+        shell: bash
+        run: ctest --preset ci-release -C ${{ matrix.build_type }} --output-on-failure
+
+      # ── 11. 构建时间摘要 ──────────────────────────────────
+      - name: Build time summary
+        if: always()
+        shell: bash
+        run: |
+          DURATION="${{ steps.build.outputs.duration }}"
+          echo "| Platform | Compiler | Build Time |" >> $GITHUB_STEP_SUMMARY
+          echo "|----------|----------|-----------|" >> $GITHUB_STEP_SUMMARY
+          echo "| ${{ matrix.os }} | ${{ (runner.os == 'Linux' && 'clang-18') || 'clang-cl' }} | ${DURATION}s |" >> $GITHUB_STEP_SUMMARY
+          echo "CI build: ${{ matrix.os }} / ${{ (runner.os == 'Linux' && 'clang-18') || 'clang-cl' }} wall time ${DURATION}s"