W22: coverage metric + network tests + Tool stream feedback + stdin pipe + session path + dependency check (W22.1-W22.6)

- W22.1: gcovr 覆盖率度量 + CI coverage job（40% 阈值 warning）
- W22.2: network_plugin 单元测试（parse_headers_json/extract_host_port/SSE/异常保护）
- W22.3: Tool Calling 流式反馈（chat_stream + "[工具调用]/[工具结果]" 状态行）
- W22.4: --prompt stdin pipe（--prompt - 从 stdin 读取）
- W22.5: session 路径健壮化（static 缓存 + mkdir + fallback）
- W22.6: 插件依赖拓扑静态校验（validate_dependencies 循环/缺失检测）

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

.github/workflows/ci.yml

@@ -224,3 +224,107 @@ jobs:
       - name: Test (Sanitizer)
         shell: bash
         run: ctest --preset ci-sanitize --output-on-failure
+
+  # ── Coverage (PR + push master, Linux clang-18, gcovr) ──
+  coverage:
+    name: Coverage (gcovr) / ubuntu-24.04
+    runs-on: ubuntu-24.04
+
+    steps:
+      # ── 1. 源码检出 ──────────────────────────────────────
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+
+      # ── 2. 工具链 (clang-18) ─────────────────────────────
+      - name: Install toolchain (Ubuntu)
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y -qq clang-18 ninja-build
+          echo "CC=clang-18" >> $GITHUB_ENV
+          echo "CXX=clang++-18" >> $GITHUB_ENV
+
+      # ── 3. Python + Conan ─────────────────────────────────
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install Conan + gcovr
+        run: pip install conan gcovr
+
+      # ── 4. Conan 依赖缓存 ─────────────────────────────────
+      - name: Cache Conan
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.conan2
+            ~/.conan2/p
+          key: ${{ runner.os }}-conan-Release-${{ hashFiles('deps/conanfile.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-conan-Release-
+            ${{ runner.os }}-conan-
+
+      # ── 5. Conan 依赖安装 ─────────────────────────────────
+      - name: Install Conan dependencies
+        shell: bash
+        run: |
+          conan profile detect --force
+          conan install deps --build=missing -s build_type=Release
+
+      # ── 6. CMake 配置 ─────────────────────────────────────
+      - name: Configure CMake (Coverage)
+        shell: bash
+        run: cmake --preset ci-coverage
+
+      # ── 7. 构建 ───────────────────────────────────────────
+      - name: Build (Coverage)
+        shell: bash
+        run: cmake --build --preset ci-coverage
+
+      # ── 8. 测试 ──────────────────────────────────────────
+      - name: Test (Coverage)
+        shell: bash
+        run: ctest --preset ci-coverage --output-on-failure
+
+      # ── 9. 覆盖率报告 ────────────────────────────────────
+      - name: Coverage report
+        id: coverage
+        shell: bash
+        run: |
+          gcovr -r . --object-directory=build/ci-coverage \
+            --gcov-executable "llvm-cov-18 gcov" \
+            --print-summary > coverage_summary.txt 2>&1 || true
+          cat coverage_summary.txt
+          # Extract line coverage percentage
+          LINE_COV=$(grep -oP 'lines:\s*\K[\d.]+' coverage_summary.txt || echo "0")
+          echo "line_rate=${LINE_COV}" >> $GITHUB_OUTPUT
+          # Also generate HTML report
+          mkdir -p build/ci-coverage/coverage
+          gcovr -r . --object-directory=build/ci-coverage \
+            --gcov-executable "llvm-cov-18 gcov" \
+            --html --html-details \
+            -o build/ci-coverage/coverage/index.html || true
+          echo "HTML report: build/ci-coverage/coverage/index.html"
+
+      # ── 10. 覆盖率摘要 + 阈值门禁 ─────────────────────────
+      - name: Coverage summary
+        if: always()
+        shell: bash
+        run: |
+          LINE_COV="${{ steps.coverage.outputs.line_rate }}"
+          THRESHOLD=40
+          echo "## Coverage Report" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "| Metric | Value | Threshold | Status |" >> $GITHUB_STEP_SUMMARY
+          echo "|--------|-------|-----------|--------|" >> $GITHUB_STEP_SUMMARY
+          if [ -z "$LINE_COV" ] || [ "$LINE_COV" = "0" ]; then
+            echo "| Line Coverage | N/A | ${THRESHOLD}% | :grey_question: (no data) |" >> $GITHUB_STEP_SUMMARY
+          elif awk "BEGIN {exit !($LINE_COV < $THRESHOLD)}"; then
+            echo "| Line Coverage | ${LINE_COV}% | ${THRESHOLD}% | :warning: BELOW THRESHOLD |" >> $GITHUB_STEP_SUMMARY
+            echo "::warning title=Coverage below threshold::Line coverage ${LINE_COV}% is below ${THRESHOLD}% threshold"
+          else
+            echo "| Line Coverage | ${LINE_COV}% | ${THRESHOLD}% | :white_check_mark: OK |" >> $GITHUB_STEP_SUMMARY
+            echo "Line coverage ${LINE_COV}% >= ${THRESHOLD}% threshold - OK"
+          fi