ci(coverage): Add cargo-tarpaulin code coverage to CI workflow

Add automated code coverage generation and reporting to Codecov using
cargo-tarpaulin. This enhances CI/CD pipeline with continuous coverage
monitoring on every push and pull request.

**Changes:**

1. Added cargo-tarpaulin Installation Step
   - Linux/macOS only (Windows excluded due to limited test coverage)
   - Installs latest tarpaulin via 'cargo install'
   - Conditional execution: matrix.os != 'windows-latest'

2. Added Coverage Generation Step
   - Command: cargo tarpaulin --workspace --locked --lib --bins --tests
   - Excludes: prtip-network, prtip-scanner (consistent with test strategy)
   - Output: Cobertura XML format in ./coverage/ directory
   - Timeout: 300 seconds (5 minutes) to prevent CI hangs
   - Environment: PRTIP_DISABLE_HISTORY=1 (prevents test race conditions)

3. Updated Codecov Upload Action
   - Changed: codecov/test-results-action@v1 → codecov/codecov-action@v4
   - Reason: test-results-action expects JUnit XML (test results),
             codecov-action@v4 expects Cobertura XML (coverage data)
   - File path: ./coverage/cobertura.xml (explicit for reliability)
   - fail_ci_if_error: false (don't block CI on coverage upload failures)
   - verbose: true (detailed logging for troubleshooting)
   - Conditional: matrix.os != 'windows-latest' && !cancelled()

**Technical Details:**

- Tarpaulin generates Cobertura XML (coverage %), not JUnit XML (test results)
- Previous action (test-results-action) expected wrong format
- New action (codecov-action@v4) correctly handles coverage data
- Coverage scope matches existing test execution strategy
- Linux/macOS only (tarpaulin compatibility)

**Impact:**

- ✅ Automated coverage reporting on every CI run
- ✅ Codecov integration for coverage tracking and visualization
- ✅ Maintains all existing CI workflows (7/7 jobs)
- ✅ Zero impact on test execution (coverage runs after tests)
- ✅ No breaking changes to existing infrastructure

**Files Modified:**
- .github/workflows/ci.yml: +18 lines (3 new steps, 1 modified)
- CHANGELOG.md: +12 lines (Changed section entry)

**Verification:**
- Workflow syntax: Valid YAML
- Conditionals: Properly formatted for GitHub Actions
- File paths: Explicit and correct
- Codecov action: Latest v4 with correct parameters

**Strategic Value:**

Establishes continuous coverage monitoring infrastructure for ProRT-IP.
Enables data-driven decisions for test coverage improvements and ensures
code quality metrics are tracked across all development phases.

Supports Phase 6 goals: Comprehensive testing, quality metrics, professional
development practices. Aligns with existing coverage reporting from Sprint 5.6
(54.92% baseline, automated CI tracking).

Related: Sprint 5.6 Coverage Enhancement (commit ed9c991)
See: CHANGELOG.md for complete Sprint 6.3 progress

Author: doublegate

.github/workflows/ci.yml

@@ -170,11 +170,28 @@ jobs:
       # Release artifacts are built in the dedicated release.yml workflow.
       # CI purpose is testing (debug builds sufficient for test validation).
 
-      - name: Upload test results to Codecov
-        if: ${{ !cancelled() }}
-        uses: codecov/test-results-action@v1
+      - name: Install cargo-tarpaulin
+        if: matrix.os != 'windows-latest'
+        run: cargo install cargo-tarpaulin
+
+      - name: Generate test coverage with tarpaulin
+        if: matrix.os != 'windows-latest'
+        run: |
+          cargo tarpaulin --workspace --locked --lib --bins --tests \
+            --exclude prtip-network --exclude prtip-scanner \
+            --out Xml --output-dir ./coverage \
+            --timeout 300
+        env:
+          PRTIP_DISABLE_HISTORY: "1"
+
+      - name: Upload test coverage to Codecov
+        if: ${{ !cancelled() && matrix.os != 'windows-latest' }}
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
+          files: ./coverage/cobertura.xml
+          fail_ci_if_error: false
+          verbose: true
 
   # Job 4: Security audit
   security_audit:

CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- **CI/CD: Added Code Coverage with cargo-tarpaulin** (2025-11-15)
+  - Added cargo-tarpaulin installation step to CI workflow (Linux/macOS only)
+  - Added coverage generation step using `cargo tarpaulin --workspace --locked --lib --bins --tests`
+  - Generates Cobertura XML output in `./coverage/` directory
+  - Changed Codecov upload from `test-results-action@v1` to `codecov-action@v4` (correct action for coverage data)
+  - Excludes `prtip-network` and `prtip-scanner` crates (consistent with existing test strategy)
+  - Windows platform excluded (limited test coverage already, tarpaulin Linux/macOS only)
+  - Coverage timeout: 300 seconds (5 minutes) to prevent CI hangs
+  - **Impact:** Automated code coverage reporting to Codecov on every CI run
+
 ### Fixed
 
 - **Test Infrastructure: macOS batch_coordination.rs Test Failures** (2025-11-15)