diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c88015776..93a2602a5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -50,13 +50,31 @@ jobs:
         with:
           python-version: '3.11'
           cache: 'pip'
+          cache-dependency-path: |
+            requirements.txt
+            requirements-ci.txt
       - name: 📦 Install dependencies
         run: |
-          pip install --upgrade pip
-          pip install -r requirements.txt
-          pip install flake8 pytest
-      - name: ✅ Run backend gate
-        run: ./scripts/ci_gate.sh
+          python -m pip install --upgrade pip
+          for attempt in 1 2 3; do
+            if python -m pip install -r requirements-ci.txt; then
+              break
+            fi
+            if [ "$attempt" -eq 3 ]; then
+              echo "Dependency install failed after ${attempt} attempts." >&2
+              exit 1
+            fi
+            echo "Dependency install attempt ${attempt} failed, retrying in 15s..." >&2
+            sleep 15
+          done
+      - name: ✅ Python syntax check
+        run: ./scripts/ci_gate.sh syntax
+      - name: ✅ Flake8 critical checks
+        run: ./scripts/ci_gate.sh flake8
+      - name: ✅ Local deterministic checks
+        run: ./scripts/ci_gate.sh deterministic
+      - name: ✅ Offline test suite
+        run: ./scripts/ci_gate.sh offline-tests
 
   docker-build:
     name: docker-build
diff --git a/requirements-ci.txt b/requirements-ci.txt
new file mode 100644
index 000000000..e145b8351
--- /dev/null
+++ b/requirements-ci.txt
@@ -0,0 +1,6 @@
+# Backend CI dependencies.
+-r requirements.txt
+
+# Test and lint tooling used by backend-gate.
+flake8
+pytest
diff --git a/requirements.txt b/requirements.txt
index f4c8716dc..7bc0acaac 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -29,7 +29,8 @@ numpy>=1.24.0               # 数值计算
 json-repair>=0.55.1         # JSON 修复
 
 # AI 分析
-litellm>=1.80.10            # Unified LLM client (Gemini/Anthropic/OpenAI/DeepSeek etc.)
+# PyPI project was quarantined on 2026-03-24; install from the upstream GitHub stable tag for now.
+litellm @ https://github.com/BerriAI/litellm/archive/refs/tags/v1.82.3-stable.patch.2.tar.gz  # Unified LLM client (Gemini/Anthropic/OpenAI/DeepSeek etc.)
 tiktoken>=0.8.0,<0.12.0    # BPE tokenizer for LLM token counting (pin <0.12 to avoid plugin registration issues, #537)
 openai>=1.0.0               # OpenAI SDK (transitive dependency of litellm, kept explicit)
 PyYAML>=6.0                 # YAML parser for LITELLM_CONFIG support
diff --git a/scripts/ci_gate.sh b/scripts/ci_gate.sh
index 687879339..bfd85ffef 100755
--- a/scripts/ci_gate.sh
+++ b/scripts/ci_gate.sh
@@ -2,20 +2,58 @@
 
 set -euo pipefail
 
-echo "==> backend-gate: Python syntax check"
-python -m py_compile main.py src/config.py src/auth.py src/analyzer.py src/notification.py
-python -m py_compile src/storage.py src/scheduler.py src/search_service.py
-python -m py_compile src/market_analyzer.py src/stock_analyzer.py
-python -m py_compile data_provider/*.py
+syntax_check() {
+  echo "==> backend-gate: Python syntax check"
+  python -m py_compile main.py src/config.py src/auth.py src/analyzer.py src/notification.py
+  python -m py_compile src/storage.py src/scheduler.py src/search_service.py
+  python -m py_compile src/market_analyzer.py src/stock_analyzer.py
+  python -m py_compile data_provider/*.py
+}
 
-echo "==> backend-gate: flake8 critical checks"
-flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+flake8_checks() {
+  echo "==> backend-gate: flake8 critical checks"
+  flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+}
 
-echo "==> backend-gate: local deterministic checks"
-./test.sh code
-./test.sh yfinance
+deterministic_checks() {
+  echo "==> backend-gate: local deterministic checks"
+  ./test.sh code
+  ./test.sh yfinance
+}
 
-echo "==> backend-gate: offline test suite"
-python -m pytest -m "not network"
+offline_test_suite() {
+  echo "==> backend-gate: offline test suite"
+  python -m pytest -m "not network"
+}
 
-echo "==> backend-gate: all checks passed"
+run_all() {
+  syntax_check
+  flake8_checks
+  deterministic_checks
+  offline_test_suite
+  echo "==> backend-gate: all checks passed"
+}
+
+phase="${1:-all}"
+
+case "$phase" in
+  all)
+    run_all
+    ;;
+  syntax)
+    syntax_check
+    ;;
+  flake8)
+    flake8_checks
+    ;;
+  deterministic)
+    deterministic_checks
+    ;;
+  offline-tests)
+    offline_test_suite
+    ;;
+  *)
+    echo "Usage: $0 [all|syntax|flake8|deterministic|offline-tests]" >&2
+    exit 2
+    ;;
+esac