docs: add v0.2.1 changelog entry with complete release notes

- Add comprehensive changelog entry for v0.2.1 patch release
- Include fixes for CI workflows, merge conflicts, and performance benchmarks
- Document performance optimizations and caching improvements
- List version updates and GitHub Actions improvements
- Add commit summary for complete traceability

Author: d-oit

CHANGELOG.md

@@ -5,6 +5,31 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.1] - 2025-10-24
+
+### Fixed
+- Fixed YAML syntax error in enhanced-ci workflow preflight job
+- Resolved merge conflicts in Cargo files during release process
+- Fixed Criterion.rs benchmark sample size assertion failures in performance tests
+
+### Performance
+- Optimized Enhanced CI workflow with improved caching (84% complexity reduction)
+- Enabled sccache with RUSTC_WRAPPER for faster compilation
+- Consolidated 15+ duplicate cache configurations into 4 optimized strategies
+- Added hierarchical cache restore keys for better hit rates
+
+### Changed
+- Updated all crate versions from 0.2.0 to 0.2.1
+- Updated to latest GitHub Actions (actions/cache@v4, checkout@v4)
+- Improved benchmark configurations with proper sample sizes and measurement times
+
+### Commits
+- chore: bump version to 0.2.1
+- fix: correct indentation in changelog-sync workflow Python script
+- fix: resolve merge conflicts in Cargo files and fix changelog-sync workflow  
+- perf: optimize enhanced-ci workflow with improved caching and reduced duplication
+- fix: resolve Criterion.rs benchmark sample size assertion failures
+
 ## [0.1.10] - 2025-10-23
 
 ### 🚀 Features

crates/core/benches/performance_comparison.rs

@@ -59,6 +59,8 @@ fn bench_small_codebase(c: &mut Criterion) {
     let _detectors = DetectorProfile::Comprehensive.get_detectors();
 
     let mut group = c.benchmark_group("small_codebase");
+    group.sample_size(20); // Good sample size for fast tests
+    group.measurement_time(std::time::Duration::from_secs(5)); // Quick measurement for small tests
 
     // Standard scanner
     group.bench_with_input(
@@ -111,7 +113,8 @@ fn bench_medium_codebase(c: &mut Criterion) {
     let _detectors = DetectorProfile::Comprehensive.get_detectors();
 
     let mut group = c.benchmark_group("medium_codebase");
-    group.sample_size(10); // Fewer samples for larger tests
+    group.sample_size(15); // Adequate samples for statistical analysis
+    group.measurement_time(std::time::Duration::from_secs(8)); // Reasonable measurement time
 
     // Standard scanner
     group.bench_with_input(
@@ -163,7 +166,8 @@ fn bench_large_codebase(c: &mut Criterion) {
     let _detectors = DetectorProfile::Comprehensive.get_detectors();
 
     let mut group = c.benchmark_group("large_codebase");
-    group.sample_size(5); // Even fewer samples for largest tests
+    group.sample_size(10); // Minimum required samples for statistical analysis
+    group.measurement_time(std::time::Duration::from_secs(15)); // Longer measurement time for stability
 
     // Skip standard scanner for large tests (too slow)
 
@@ -204,6 +208,8 @@ fn bench_cache_performance(c: &mut Criterion) {
     let _detectors = DetectorProfile::Comprehensive.get_detectors();
 
     let mut group = c.benchmark_group("cache_performance");
+    group.sample_size(15); // Good sample size for cache performance testing
+    group.measurement_time(std::time::Duration::from_secs(6)); // Reasonable time for cache tests
 
     // Optimized scanner with cache
     group.bench_with_input(
@@ -248,6 +254,8 @@ fn bench_pattern_detection_methods(c: &mut Criterion) {
         + &"regular code line\n".repeat(2000);
 
     let mut group = c.benchmark_group("pattern_detection_methods");
+    group.sample_size(25); // Higher sample size for micro-benchmarks
+    group.measurement_time(std::time::Duration::from_secs(4)); // Fast measurement for pattern detection
 
     // Pure regex approach
     group.bench_function("regex_only", |b| {