Add .github/copilot-instructions.md for AI-assisted development

.github/copilot-instructions.md

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+# Copilot Instructions for sonic-mgmt-framework
+
+## Project Overview
+
+sonic-mgmt-framework provides the SONiC management framework, including the REST server, CLI infrastructure, and OpenAPI/YANG code generation tooling. It serves as the northbound management interface for SONiC switches, offering REST APIs and a KLISH-based CLI that translates user requests into Redis DB operations via the translib layer from `sonic-mgmt-common`. This is the user-facing management layer of the SONiC management stack.
+
+## Architecture
+
+```
+sonic-mgmt-framework/
+├── rest/                         # REST server (Go)
+│   ├── main/                     # REST server entry point
+│   │   └── main.go              # Server main()
+│   ├── server/                   # HTTP server implementation
+│   └── Makefile
+├── CLI/                          # KLISH-based CLI framework
+│   ├── clitree/                  # CLI command tree definitions (XML)
+│   ├── actioner/                 # CLI action handlers (Python scripts)
+│   ├── renderer/                 # CLI output rendering templates (J2)
+│   ├── clicfg/                   # CLI configuration files
+│   ├── klish/                    # KLISH shell framework
+│   └── Makefile
+├── models/                       # API model definitions
+│   ├── openapi/                  # OpenAPI (Swagger) specifications
+│   ├── .gitkeep
+│   ├── Makefile
+│   ├── codegen.config            # Code generation configuration
+│   ├── openapi_codegen.mk       # OpenAPI code generation rules
+│   └── yang_to_openapi.mk       # YANG-to-OpenAPI conversion rules
+├── tools/                        # Code generation and development tools
+│   ├── codegen/                  # API server code generator
+│   ├── pyang/                    # pyang YANG processing plugins
+│   ├── swagger_codegen/          # Swagger code generation
+│   ├── restconf_doc_tools/       # RESTCONF documentation generators
+│   ├── openapi_tests/            # OpenAPI validation tests
+│   ├── ui_gen/                   # UI generation tools
+│   └── test/                     # Test utilities
+├── debian/                       # Debian packaging
+├── Makefile                      # Top-level build orchestration
+└── .github/                      # CI workflows
+```
+
+### Key Concepts
+- **REST server**: Go-based HTTP server that exposes RESTCONF/OpenAPI endpoints and delegates to translib for DB operations
+- **KLISH CLI**: XML-defined command tree with Python actioners that call REST APIs or directly interact with SONiC
+- **OpenAPI code generation**: YANG models are converted to OpenAPI specs, which then generate Go server stubs
+- **Actioner pattern**: CLI commands trigger Python scripts in `CLI/actioner/` that format requests and call REST endpoints
+- **Renderer pattern**: CLI output is formatted using Jinja2 templates in `CLI/renderer/`
+
+## Language & Style
+
+- **Primary languages**: Go (REST server), Python (CLI actioners, tools), XML (CLI tree definitions)
+- **Secondary**: Jinja2 (renderers), YANG (models), Shell scripts
+- **Go conventions**:
+  - Standard `gofmt` formatting
+  - Types/Functions: `PascalCase` for exported, `camelCase` for unexported
+  - File names: `snake_case.go`
+- **Python conventions**:
+  - PEP 8 compliant
+  - 4 spaces indentation
+  - CLI actioner scripts are standalone executables
+- **XML CLI definitions**: Follow KLISH XML schema for command tree structure
+- **Jinja2 templates**: Use `.j2` extension; follow existing template patterns in `CLI/renderer/`
+
+## Build Instructions
+
+```bash
+# Full build requires sonic-buildimage environment
+# For standalone development:
+
+# Build REST server
+cd rest
+make
+
+# Build CLI
+cd CLI
+make
+
+# Build models / code generation
+cd models
+make
+
+# Build Debian package (in sonic-buildimage context)
+BLDENV=stretch make target/debs/stretch/sonic-mgmt-framework_1.0-01_amd64.deb
+
+# Build Docker container
+BLDENV=stretch make target/docker-sonic-mgmt-framework.gz
+
+# Incremental rebuild
+BLDENV=stretch make target/debs/stretch/sonic-mgmt-framework_1.0-01_amd64.deb-clean
+BLDENV=stretch make target/debs/stretch/sonic-mgmt-framework_1.0-01_amd64.deb
+```
+
+## Testing
+
+```bash
+# REST server tests
+cd rest
+go test -v ./...
+
+# OpenAPI validation tests
+cd tools/openapi_tests
+# Run validation against generated specs
+
+# CLI testing is typically done in integration environments
+# Manual testing: Load CLI tree in KLISH and verify commands
+
+# Tool tests
+cd tools/test
+# Run tool-specific tests
+```
+
+## PR Guidelines
+
+- **Signed-off-by**: REQUIRED on all commits (`git commit -s`)
+- **CLA**: Sign the Linux Foundation EasyCLA
+- **Single commit per PR**: Squash commits before merge
+- **CLI changes**: Include XML tree definitions, actioner scripts, and renderer templates together
+- **REST API changes**: Update OpenAPI specs and verify generated code
+- **YANG model changes**: Coordinate with `sonic-mgmt-common` for model updates
+- **Reference**: Link SONiC management framework design documents in PR
+
+## Dependencies
+
+- **sonic-mgmt-common**: Provides translib, CVL, and YANG models (core dependency)
+- **sonic-swss-common**: Redis DB access (via translib)
+- **KLISH**: CLI shell framework (embedded in `CLI/klish/`)
+- **pyang**: YANG model processing
+- **swagger-codegen**: OpenAPI code generation
+- **Go standard library**: HTTP server, JSON, etc.
+- **Jinja2**: Python template engine for CLI rendering
+- **sonic-buildimage**: Full build environment
+
+## Gotchas
+
+- **Build environment**: Full builds require the `sonic-buildimage` Docker environment; standalone builds only work for individual components
+- **Code generation**: Much of the REST server code is auto-generated from OpenAPI specs — don't manually edit generated files
+- **YANG ↔ OpenAPI sync**: Changes to YANG models in `sonic-mgmt-common` must be reflected in OpenAPI specs here
+- **CLI tree ordering**: KLISH XML tree files have include dependencies; incorrect ordering causes CLI load failures
+- **Actioner path**: CLI actioners must be executable and have correct shebang lines
+- **Renderer templates**: Jinja2 templates must handle both empty results and error cases
+- **Python path**: CLI actioners may need `PYTHONPATH` set to find SONiC Python libraries
+- **REST authentication**: The REST server supports certificate-based auth; test with proper certs
+- **Incremental builds**: Use `-clean` make targets before rebuilding specific components
+- **Model interdependencies**: OpenAPI specs may import types from other specs; verify cross-references