fix(multicall): resolve critical multicall parsing corruption issues

- Added comprehensive bounds checking to prevent buffer overruns in multicall parsing
- Implemented graduated validation system (Strict/Moderate/Permissive) to reduce false positives
- Added LRU caching system for address validation with 10-minute TTL
- Enhanced ABI decoder with missing Universal Router and Arbitrum-specific DEX signatures
- Fixed duplicate function declarations and import conflicts across multiple files
- Added error recovery mechanisms with multiple fallback strategies
- Updated tests to handle new validation behavior for suspicious addresses
- Fixed parser test expectations for improved validation system
- Applied gofmt formatting fixes to ensure code style compliance
- Fixed mutex copying issues in monitoring package by introducing MetricsSnapshot
- Resolved critical security vulnerabilities in heuristic address extraction
- Progress: Updated TODO audit from 10% to 35% complete

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/8_reports/enhancements/detection_engine_plan.md

@@ -0,0 +1,33 @@
+# Detection Engine Hardening Plan
+
+## Objectives
+Ensure the detection pipeline produces actionable opportunities with production-grade heuristics and hands them off to the execution stack automatically. Current implementation primarily logs opportunities and uses simplified scoring parameters.
+
+## Action Items
+
+1. **Opportunity Scoring & Filtering**
+   - [ ] Define canonical scoring function (profitability, confidence, liquidity, latency) aligned with business thresholds.
+   - [ ] Replace ad-hoc ROI/price-impact checks with configurable policies (pull from config/env).
+   - [ ] Add regression tests covering borderline cases (low confidence, high slippage, gas-constrained opportunities).
+
+2. **Execution Handoff**
+   - [x] Implement direct handoff to `ArbitrageExecutor` via callback (see `SetOpportunityHandler`).
+   - [ ] Ensure backpressure handling (bounded queue, metrics when saturated).
+   - [ ] Introduce retry/backoff for transient execution failures.
+
+3. **Concurrency & Worker Pools**
+   - [ ] Review `WorkerPool` sizing, ensure graceful shutdown and error propagation.
+   - [ ] Add instrumentation (metrics/logs) for scan time, queue depth, dropped opportunities.
+
+4. **Historical Validation**
+   - [ ] Replay recorded blocks/datasets to validate hit rate and false positives.
+   - [ ] Store misclassified opportunities for manual review.
+
+5. **Configuration & Docs**
+   - [ ] Centralise detection thresholds in config files (`config/*.yaml`) and document in `docs/5_development/CONFIGURATION.md`.
+   - [ ] Update runbooks to describe detection tuning knobs and alerting thresholds.
+
+## References
+- `pkg/arbitrage/detection_engine.go`
+- `pkg/arbitrage/service.go` (execution integration)
+- `pkg/metrics` for instrumentation