Add Codex instructions

AGENT.md

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+# Instructions for OpenAI Codex
+
+This file provides guidelines for OpenAI Codex to ensure code quality and consistency within this project.
+
+## General Instructions
+
+1. **Follow Existing Code Style**: Adhere to the style already present in the repository.
+2. **Use TypeScript**: All new code must be written in TypeScript.
+3. **Meaningful Names**: Use descriptive names for variables and functions.
+4. **Comments**: Comment complex logic to explain its purpose.
+
+## Testing
+
+1. **Testing Framework**: Use Mocha and Chai for tests.
+2. **Run Tests**: Compile the project then run `npm test` to execute all tests.
+3. **Test Files**: Maintain and extend existing test files when adding new functionality.
+
+## Commands
+
+1. **Build**: `npm run build`
+2. **Run All Tests**: `npm test`
+3. **Watch Tests**: `npm run test_watch`
+4. **Coverage**: `npm run cover`
+5. **Lint**: `npx tslint -c tslint.json -p tsconfig.json`
+
+## Pull Request Guidelines
+
+1. **Description**: Provide a clear description of the changes.
+2. **Related Issues**: Reference any related issues.
+3. **Tests**: Ensure all tests pass before submission.
+4. **Single Concern**: Keep pull requests focused on a single concern.
+
+## Important
+
+After making any changes, Codex MUST run `npm run build` and `npm test` to confirm that the build and tests pass.