Set up GitHub Copilot instructions for repository

.github/copilot-instructions.md

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+# GitHub Copilot Instructions for Mina Rust Repository
+
+## Project Overview
+
+Mina is a Rust implementation of the Mina Protocol, a lightweight blockchain
+using zero-knowledge proofs. It follows a Redux-style state machine architecture
+for predictable, debuggable behavior.
+
+## Architecture
+
+### State Machine Pattern
+
+The codebase follows Redux principles:
+
+- **State** - Centralized, immutable data structure
+- **Actions** - Events that trigger state changes
+- **Enabling Conditions** - Guards that prevent invalid state transitions
+- **Reducers** - Functions that update state and dispatch new actions
+- **Effects** - Thin wrappers for service calls
+- **Services** - Separate threads handling I/O and heavy computation
+
+### Key Components
+
+- **node/** - Main node logic (block production, transaction pool, consensus)
+- **p2p/** - Networking layer (libp2p and WebRTC transports)
+- **snark/** - Proof verification orchestration
+- **ledger/** - Ledger implementation and transaction logic
+- **core/** - Shared types and utilities
+
+## Code Patterns
+
+### File Organization
+
+- `*_state.rs` - State definitions
+- `*_actions.rs` - Action types
+- `*_reducer.rs` - State transitions
+- `*_effects.rs` - Service interactions
+- `*_service.rs` - Service interfaces
+
+### Defensive Programming
+
+- Use `bug_condition!` macro for theoretically unreachable code paths
+- Always add enabling condition checks before state transitions
+- Extract complex logic from reducers into state methods
+
+## Development Workflow
+
+### Before Making Changes
+
+1. Understand the Redux-style architecture
+2. Identify the correct component and layer for your changes
+3. Check existing patterns in similar files
+4. Run tests to understand current behavior
+
+### Code Changes
+
+1. Make minimal, surgical modifications
+2. Follow existing patterns and conventions
+3. Update documentation if directly related to changes
+4. Preserve working functionality
+
+### Formatting and Quality
+
+**MANDATORY before any commit:**
+
+```bash
+# Format Rust and TOML files
+make format
+
+# Format markdown and MDX files
+make format-md
+
+# Fix trailing whitespaces (CRITICAL)
+make fix-trailing-whitespace
+
+# Verify formatting
+make check-format
+make check-md
+make check-trailing-whitespace
+```
+
+### Testing
+
+```bash
+# Run all tests
+make test
+
+# Run specific test suites
+make test-p2p
+make test-ledger
+make nextest  # Faster test execution
+
+# Build project
+make build
+make build-release
+```
+
+### Documentation
+
+- Update `CHANGELOG.md` for significant user-facing changes
+- Use format: `- **Category**: Description ([#PR](github-link))`
+- Component docs are in individual `summary.md` files
+- Website docs are in `website/docs/`
+
+## Commit Guidelines
+
+**CRITICAL RULES:**
+
+- **NEVER** add any AI assistant as co-author in commit messages
+- **NEVER** use emojis in commit messages
+- **ALWAYS** wrap commit titles at 80 characters
+- **ALWAYS** run `make fix-trailing-whitespace` before committing
+
+### Commit Message Format
+
+```
+Brief description of change (80 chars max)
+
+Longer description if needed, wrapped at 80 characters.
+Reference issues/PRs when relevant.
+```
+
+## Code Style
+
+### Rust Code
+
+- Follow existing `rustfmt` configuration
+- Use `clippy` suggestions: `make lint`
+- Prefer explicit error handling over panics
+- Use descriptive variable names
+- Add comments only when they add value beyond the code
+
+### Documentation Style
+
+- Use lowercase for section headings ("test design", "resource management")
+- Use lowercase for bullet point labels
+- Wrap Docusaurus admonitions with prettier-ignore comments:
+
+  ```mdx
+  <!-- prettier-ignore-start -->
+
+  :::note Content here :::
+
+  <!-- prettier-ignore-stop -->
+  ```
+
+## Common Tasks
+
+### Adding New Features
+
+1. Define actions in appropriate `*_actions.rs`
+2. Add state transitions in `*_reducer.rs`
+3. Implement effects in `*_effects.rs` if needed
+4. Add service methods in `*_service.rs` if needed
+5. Update tests and documentation
+
+### Debugging
+
+- Use existing test scenarios in `node/testing/`
+- Check component `summary.md` files for known issues
+- Follow the Redux flow: Action → Reducer → Effect → Service
+
+### Dependencies
+
+- Update `Cargo.toml` files carefully
+- Run `make check` after dependency changes
+- Consider impact on WebAssembly build (`make build-wasm`)
+
+## Important Files
+
+- `node/src/state.rs` - Global state structure
+- `node/src/action.rs` - Top-level action enum
+- `node/src/reducer.rs` - Main reducer dispatch
+- `Makefile` - Build and development commands
+- `CLAUDE.md` - Comprehensive codebase navigation guide
+- `ARCHITECTURE.md` - Migration guide for old vs new style
+
+## Resources
+
+- Architecture docs: `docs/handover/`
+- Component docs: Find `summary.md` in component directories
+- Website: `make docs-serve` (http://localhost:3000)
+- Build commands: `make help`
+
+Remember: This is a complex blockchain implementation. Take time to understand
+the Redux architecture and existing patterns before making changes.