feat(coprocessor): add cargo-llvm-cov code coverage to Rust CI workflows

.github/workflows/coprocessor-cargo-tests.yml

@@ -53,7 +53,13 @@ jobs:
     - name: Setup Rust
       uses: dtolnay/rust-toolchain@a54c7afa936fefeb4456b2dd8068152669aa8203
       with:
-        toolchain: stable
+        toolchain: "1.91.1"
+        components: llvm-tools-preview
+
+    - name: Install cargo-llvm-cov
+      uses: taiki-e/install-action@a37010ded18ff788be4440302bd6830b1ae50d8b # v2.68.25
+      with:
+        tool: cargo-llvm-cov
 
     - name: Install cargo dependencies
       run: |
@@ -71,8 +77,8 @@ jobs:
           ~/.cargo/registry
           ~/.cargo/git
           target
-        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-        restore-keys: ${{ runner.os }}-cargo-
+        key: ${{ runner.os }}-cargo-coverage-${{ hashFiles('**/Cargo.lock') }}
+        restore-keys: ${{ runner.os }}-cargo-coverage-
 
     - name: Login to GitHub Container Registry
       uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
@@ -101,7 +107,26 @@ jobs:
       run: |
         docker run --rm -d -p 4566:4566 --name localstack localstack/localstack:latest
 
-    - name: Run tests
+    - name: Run tests with coverage
+      run: |
+        DATABASE_URL=postgresql://postgres:postgres@localhost:5432/coprocessor \
+        TEST_GLOBAL_LOCALSTACK=1 \
+        cargo llvm-cov --workspace --profile coverage -- --test-threads=1
+      working-directory: coprocessor/fhevm-engine
+
+    - name: Coverage summary
+      if: always()
       run: |
-        DATABASE_URL=postgresql://postgres:postgres@localhost:5432/coprocessor TEST_GLOBAL_LOCALSTACK=1 cargo test --release -- --test-threads=1
+        REPORT=$(DATABASE_URL=postgresql://postgres:postgres@localhost:5432/coprocessor \
+          cargo llvm-cov report --workspace --profile coverage 2>/dev/null) || true
+        {
+          echo '## Coverage: coprocessor/fhevm-engine'
+          if [ -n "$REPORT" ]; then
+            echo '```'
+            echo "$REPORT"
+            echo '```'
+          else
+            echo '*No coverage data available (tests may have failed before producing profiling data).*'
+          fi
+        } >> "$GITHUB_STEP_SUMMARY"
       working-directory: coprocessor/fhevm-engine

coprocessor/fhevm-engine/Cargo.toml

@@ -111,3 +111,10 @@ inherits = "release"
 opt-level = 1
 lto = false
 codegen-units = 16
+
+[profile.coverage]
+inherits = "release"
+opt-level = 1
+lto = false
+debug = 1
+codegen-units = 16

coprocessor/fhevm-engine/rust-toolchain.toml

@@ -1,2 +1,3 @@
 [toolchain]
 channel = "1.91.1"
+components = ["llvm-tools-preview"]