DOC: Add llms.txt and copilot-instructions.md for LLM guidance

.github/copilot-instructions.md

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+# Copilot Instructions for mssql-python
+
+## Repository Overview
+
+**mssql-python** is a Python driver for Microsoft SQL Server and Azure SQL databases that leverages Direct Database Connectivity (DDBC). It's built using **pybind11** and **CMake** to create native extensions, providing DB API 2.0 compliant database access with enhanced Pythonic features.
+
+- **Size**: Medium-scale project (~750KB total)
+- **Languages**: Python (main), C++ (native bindings), CMake (build system)
+- **Target Platforms**: Windows (x64, ARM64), macOS (Universal2), Linux (x86_64, ARM64)
+- **Python Versions**: 3.10+
+- **Key Dependencies**: pybind11, azure-identity, Microsoft ODBC Driver 18
+
+## Usage Examples (For Suggesting to Users)
+
+### Basic Connection and Query
+```python
+import mssql_python
+
+conn = mssql_python.connect(
+    "SERVER=localhost;DATABASE=mydb;Trusted_Connection=yes;Encrypt=yes;TrustServerCertificate=yes"
+)
+cursor = conn.cursor()
+cursor.execute("SELECT * FROM users WHERE id = ?", (user_id,))
+rows = cursor.fetchall()
+cursor.close()
+conn.close()
+```
+
+### Context Manager (Recommended)
+```python
+with mssql_python.connect(connection_string) as conn:
+    with conn.cursor() as cursor:
+        cursor.execute("SELECT @@VERSION")
+        print(cursor.fetchone()[0])
+```
+
+### Azure SQL with Entra ID
+```python
+conn = mssql_python.connect(
+    "SERVER=myserver.database.windows.net;DATABASE=mydb;"
+    "Authentication=ActiveDirectoryInteractive;Encrypt=yes"
+)
+```
+
+### Parameterized Queries
+```python
+# Positional parameters
+cursor.execute("SELECT * FROM users WHERE email = ?", (email,))
+
+# Named parameters (pyformat)
+cursor.execute("SELECT * FROM users WHERE email = %(email)s", {"email": email})
+```
+
+### Insert with Commit
+```python
+cursor.execute("INSERT INTO users (name, email) VALUES (?, ?)", ("John", "john@example.com"))
+conn.commit()
+```
+
+### Batch Insert
+```python
+cursor.executemany("INSERT INTO users (name, email) VALUES (?, ?)", [
+    ("Alice", "alice@example.com"),
+    ("Bob", "bob@example.com"),
+])
+conn.commit()
+```
+
+### Transaction Handling
+```python
+try:
+    cursor.execute("UPDATE accounts SET balance = balance - 100 WHERE id = ?", (from_id,))
+    cursor.execute("UPDATE accounts SET balance = balance + 100 WHERE id = ?", (to_id,))
+    conn.commit()
+except Exception:
+    conn.rollback()
+    raise
+```
+
+## Build System and Validation
+
+### Prerequisites
+**Always install these before building:**
+```bash
+# All platforms
+pip install -r requirements.txt
+
+# Windows: Requires Visual Studio Build Tools with "Desktop development with C++" workload
+# macOS: brew install cmake && brew install msodbcsql18
+# Linux: Install cmake, python3-dev, and ODBC driver per distribution
+```
+
+### Building the Project
+
+**CRITICAL**: The project requires building native extensions before testing. Extensions are platform-specific (`.pyd` on Windows, `.so` on macOS/Linux).
+
+#### Windows Build:
+```bash
+cd mssql_python/pybind
+build.bat [x64|x86|arm64]  # Defaults to x64 if not specified
+```
+
+#### macOS Build:
+```bash
+cd mssql_python/pybind
+./build.sh  # Creates universal2 binary (ARM64 + x86_64)
+```
+
+#### Linux Build:
+```bash
+cd mssql_python/pybind
+./build.sh  # Detects architecture automatically
+```
+
+**Build Output**: Creates `ddbc_bindings.cp{python_version}-{architecture}.{so|pyd}` in the `mssql_python/` directory.
+
+### Testing
+
+**IMPORTANT**: Tests require a SQL Server connection via `DB_CONNECTION_STRING` environment variable.
+
+```bash
+# Run all tests with coverage
+python -m pytest -v --cov=. --cov-report=xml --capture=tee-sys --cache-clear
+
+# Run specific test files
+python -m pytest tests/test_000_dependencies.py -v  # Dependency checks
+python -m pytest tests/test_001_globals.py -v      # Basic functionality
+```
+
+**Test Dependencies**: Tests require building the native extension first. The dependency test (`test_000_dependencies.py`) validates that all platform-specific libraries exist.
+
+### Linting and Code Quality
+
+```bash
+# Python formatting
+pip install black
+black --check --line-length=100 mssql_python/ tests/
+
+# C++ formatting
+clang-format -style=file -i mssql_python/pybind/*.cpp mssql_python/pybind/*.h
+
+# Coverage reporting (configured in .coveragerc)
+python -m pytest --cov=. --cov-report=html
+```
+
+## Project Architecture
+
+### Core Components
+
+```
+mssql_python/
+├── __init__.py                    # Package initialization, connection registry, cleanup
+├── connection.py                  # DB API 2.0 connection object
+├── cursor.py                      # DB API 2.0 cursor object
+├── db_connection.py               # connect() function implementation
+├── auth.py                        # Microsoft Entra ID authentication
+├── pooling.py                     # Connection pooling implementation
+├── logging.py                     # Logging configuration
+├── exceptions.py                  # Exception hierarchy
+├── connection_string_builder.py   # Connection string construction
+├── connection_string_parser.py    # Connection string parsing
+├── parameter_helper.py            # Query parameter handling
+├── row.py                         # Row object implementation
+├── type.py                        # DB API 2.0 type objects
+├── constants.py                   # ODBC constants
+├── helpers.py                     # Utility functions and settings
+└── pybind/                        # Native extension source
+    ├── ddbc_bindings.cpp          # Main C++ binding code
+    ├── CMakeLists.txt             # Cross-platform build configuration
+    ├── build.sh/.bat              # Platform-specific build scripts
+    └── configure_dylibs.sh        # macOS dylib configuration
+```
+
+### Platform-Specific Libraries
+
+```
+mssql_python/libs/
+├── windows/{x64,x86,arm64}/          # Windows ODBC drivers and dependencies
+├── macos/{arm64,x86_64}/lib/         # macOS dylibs
+└── linux/{debian_ubuntu,rhel,suse,alpine}/{x86_64,arm64}/lib/  # Linux distributions
+```
+
+### Configuration Files
+
+- **`.clang-format`**: C++ formatting (Google style, 100 column limit)
+- **`.coveragerc`**: Coverage exclusions (main.py, setup.py, tests/)
+- **`requirements.txt`**: Development dependencies (pytest, pybind11, coverage)
+- **`setup.py`**: Package configuration with platform detection
+- **`pyproject.toml`**: Modern Python packaging configuration
+- **`.gitignore`**: Excludes build artifacts (*.so, *.pyd, build/, __pycache__)
+
+## CI/CD Pipeline Details
+
+### GitHub Workflows
+- **`devskim.yml`**: Security scanning (runs on PRs and main)
+- **`pr-format-check.yml`**: PR validation (title format, GitHub issue/ADO work item links)
+
+### Azure DevOps Pipelines (`eng/pipelines/`)
+- **`pr-validation-pipeline.yml`**: Comprehensive testing across all platforms
+- **`build-whl-pipeline.yml`**: Wheel building for distribution
+- **Platform Coverage**: Windows (LocalDB), macOS (Docker SQL Server), Linux (Ubuntu, Debian, RHEL, Alpine) with both x86_64 and ARM64
+
+### Build Matrix
+The CI system tests:
+- **Python versions**: 3.10, 3.11, 3.12, 3.13
+- **Windows**: x64, ARM64 architectures
+- **macOS**: Universal2 (ARM64 + x86_64)
+- **Linux**: Multiple distributions (Debian, Ubuntu, RHEL, Alpine) on x86_64 and ARM64
+
+## Common Build Issues and Workarounds
+
+### macOS-Specific Issues
+- **dylib path configuration**: Run `configure_dylibs.sh` after building to fix library paths
+- **codesigning**: Script automatically codesigns libraries for compatibility
+
+### Linux Distribution Differences
+- **Debian/Ubuntu**: Use `apt-get install python3-dev cmake pybind11-dev`
+- **RHEL**: Requires enabling CodeReady Builder repository for development tools
+- **Alpine**: Uses musl libc, requires special handling in build scripts
+
+### Windows Build Dependencies
+- **Visual Studio Build Tools**: Must include "Desktop development with C++" workload
+- **Architecture Detection**: Build scripts auto-detect target architecture from environment
+
+### Known Limitations (from TODOs)
+- Linux RPATH configuration pending for driver .so files
+- Some Unicode support gaps in executemany operations
+- Platform-specific test dependencies in exception handling
+
+## Architecture Detection and Loading
+
+The `ddbc_bindings.py` module implements sophisticated architecture detection:
+- **Windows**: Normalizes `win64/amd64/x64` → `x64`, `win32/x86` → `x86`, `arm64` → `arm64`
+- **macOS**: Runtime architecture detection, always loads from universal2 binary
+- **Linux**: Maps `x64/amd64` → `x86_64`, `arm64/aarch64` → `arm64`
+
+## Contributing Guidelines
+
+### PR Requirements
+- **Title Format**: Must start with `FEAT:`, `CHORE:`, `FIX:`, `DOC:`, `STYLE:`, `REFACTOR:`, or `RELEASE:`
+- **Issue Linking**: Must link to either GitHub issue or ADO work item
+- **Summary**: Minimum 10 characters of meaningful content under "### Summary"
+
+### Development Workflow
+1. **Always build native extensions first** before running tests
+2. **Use virtual environments** for dependency isolation
+3. **Test on target platform** before submitting PRs
+4. **Check CI pipeline results** for cross-platform compatibility
+
+## Trust These Instructions
+
+These instructions are comprehensive and tested. Only search for additional information if:
+- Build commands fail with unexpected errors
+- New platform support is being added
+- Dependencies or requirements have changed
+
+For any ambiguity, refer to the platform-specific README in `mssql_python/pybind/README.md` or the comprehensive CI pipeline configurations in `eng/pipelines/`.