feat: Introduce Hashline encoding/validation, implement core REPL and chat session logic, and establish initial project structure with a license and editor configuration.

IMPROVEME.md

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+# Improvements for AnchorCli
+
+This document contains criticisms and suggestions for improving the AnchorCli project.
+
+## Architecture
+
+1. **Program.cs is too large (433 lines)** - Split into smaller classes: ChatSession, ReplLoop, ResponseStreamer
+2. **No dependency injection** - Use Microsoft.Extensions.DependencyInjection for testability
+3. **Static tool classes with global Log delegates** - Convert to instance classes with injected ILogger
+
+## Testing
+
+4. **No unit tests** - Add xUnit project, test HashlineEncoder/Validator, tools, and ContextCompactor
+5. **No integration tests** - Use Spectre.Console.Testing for TUI workflows
+6. **No CI/CD** - Add GitHub Actions for test runs on push/PR
+
+## Documentation
+
+7. **Missing XML docs** - Add summary docs to public APIs
+8. **Incomplete README** - Add contributing, development, troubleshooting sections
+9. **No CHANGELOG.md** - Track releases and changes
+
+## Security & Safety
+
+10. **Command execution unsandboxed** - Add allowlist/denylist, time limits, output size limits
+11. **No mutation rate limiting** - Track edits per turn, add configurable limits
+12. **API key in plain text** - Use OS keychain or env var, set restrictive file permissions
+
+## Performance
+
+13. **No file read caching** - Cache file content per-turn with invalidation on write
+14. **Regex not static** - Make compiled regexes static readonly
+
+## User Experience
+
+15. **No undo** - Store edit history, add /undo command
+16. **No session persistence** - Add /save and /load commands
+17. **Limited error recovery** - Better error messages, /debug mode
+
+## Developer Experience
+
+18. **No .editorconfig** - Add code style enforcement
+19. **No solution file** - Create AnchorCli.sln
+20. **Hardcoded model list** - Fetch from OpenRouter API dynamically
+21. **No version info** - Add <Version> to .csproj, display in /help
+
+## Code Quality
+
+22. **Inconsistent error handling** - Standardize on error strings, avoid empty catch blocks
+23. **Magic numbers** - Extract to named constants (150_000, 300, KeepRecentTurns=2)
+24. **Commented-out debug code** - Remove or use #if DEBUG
+25. **Weak hash algorithm** - Adler-8 XOR only has 256 values; consider 4-char hex
+
+## Build & Dependencies
+
+26. **No LICENSE file** - Add MIT LICENSE file
+
+## Priority
+
+### High
+- [ ] Add unit tests
+- [ ] Implement undo functionality
+- [ ] Add mutation rate limiting
+- [x] Refactor Program.cs
+- [x] Add LICENSE file
+
+### Medium
+- [ ] Session persistence
+- [ ] XML documentation
+- [ ] Error handling consistency
+- [x] .editorconfig
+- [ ] Dynamic model list
+
+### Low
+- [ ] CHANGELOG.md
+- [ ] CI/CD pipeline
+- [ ] Stronger hash algorithm
+- [ ] Code coverage reporting
+
+## Quick Wins (<1 hour each)
+
+- [x] Add <Version> to .csproj
+- [x] Create LICENSE file
+- [x] Add .editorconfig
+- [x] Remove commented code
+- [x] Extract magic numbers to constants
+- [x] Add XML docs to Hashline classes
+- [x] Make regexes static readonly
+
+*Prioritize based on goals: safety, testability, or user experience.*