Add cleanup strategy document - consensus-safe improvements only

CLEANUP_STRATEGY.md

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+# Triangles Cleanup Strategy - Safe Improvements
+
+**Branch:** `cleanup/safe-improvements`  
+**Goal:** Improve code quality without touching consensus-critical code
+
+## ✅ SAFE TO FIX
+
+### 1. Compiler Warnings (Non-Consensus)
+- **C++11 literal-suffix warnings** - Add spaces between literals and suffixes
+- **Unused variables/functions** - Remove dead code (verify not consensus-critical first)
+- **Deprecated-copy warnings** - Fix CScript assignment operator if safe
+
+### 2. Code Style Improvements
+- Remove `using namespace std` from headers (keep in .cpp files)
+- Standardize logging patterns
+- Improve code comments (remove unclear/misleading ones)
+- Add context to TODOs/FIXMEs
+
+### 3. Documentation
+- Add inline comments for thread safety concerns
+- Document collision vulnerabilities
+- Improve function/class documentation
+
+## ❌ DO NOT TOUCH
+
+### Consensus-Critical Code
+- **OpenSSL SHA256/RIPEMD160 usage** - Deprecated warnings OK, do not change
+- **BN_is_prime_ex** - Crypto library deprecation, leave as-is
+- **Hash algorithms** - Third-party libraries with warnings, consensus-critical
+- **Block validation logic** - Any code affecting block/transaction validation
+- **Merkle tree construction** - Core consensus
+- **Proof-of-Work/Proof-of-Stake** - Staking/mining algorithms
+
+### How to Identify Consensus Code
+- Files in `src/` related to: `main.cpp`, `main.h`, block validation, transaction validation
+- Anything in hash algorithm libraries
+- Cryptographic primitives
+- Network protocol message formats (version, serialization)
+
+## Incremental Testing Strategy
+
+1. **One warning category at a time**
+2. **Compile after each change**
+3. **Test basic functionality:**
+   - `trianglesd getinfo`
+   - `trianglesd getblockchaininfo`
+   - Verify block sync works
+4. **Commit incrementally** with clear messages
+
+## Warning Categories (From Build Output)
+
+```
+1. C++11 literal-suffix: ~20 instances (util.h, net.h, alert.cpp)
+2. OpenSSL deprecation: SHA256, RIPEMD160 (DO NOT FIX)
+3. BN_is_prime_ex: crypto library (DO NOT FIX)
+4. Deprecated-copy: CScript assignment (REVIEW CAREFULLY)
+5. Unused variables/functions: Various (SAFE IF NOT CONSENSUS)
+```
+
+## Branch History
+
+- Previous work: `cleanup/desloppify` (documentation improvements, merged to master)
+- This branch: Focus on safe compiler warnings and code quality
+
+## Verification Checklist
+
+Before pushing each commit:
+- [ ] Code compiles successfully
+- [ ] No new warnings introduced
+- [ ] trianglesd runs without errors
+- [ ] getinfo/getblockchaininfo work
+- [ ] No consensus-critical code touched
+
+---
+
+**Principle:** When in doubt, don't touch it. A clean codebase is worthless if the blockchain forks.