Build 6 — Extensible Plugin Architecture (Capstone)

# Build 6: Extensible Plugin Architecture (Capstone Project) ## Scenario You are the lead software architect building an extensible core engine. Third-party developers need to write custom plugins that transform, validate, and export data without modifying your core repository. ## Requirements 1. **Interface Contracts:** Define plugin interfaces using `typing.Protocol` with runtime checkability (`@runtime_checkable`). 2. **Dynamic Discovery:** Discover and load external plugins dynamically at runtime using `importlib.metadata` entry-points and dynamic directory scanning. 3. **Hook Execution & Lifecycle:** Implement hook execution with priority weighting and fault isolation (a crashing plugin must not take down the host application). 4. **Reference Implementation:** Implement two contrasting plugins: - `JsonTransformPlugin`: Normalizes and sanitizes payloads. - `WebhookExportPlugin`: Sends processed events to an HTTP webhook with retries. 5. **Architectural Memo:** Include a 1-page `ARCHITECTURE.md` explaining your design decisions and lifecycle contracts. ## Starter Code Layout ``` build-6-plugin-capstone/ ├── ARCHITECTURE.md ├── pyproject.toml ├── src/ │ ├── plugin_engine/ │ │ ├── __init__.py │ │ ├── manager.py # Plugin registry & dynamic loader │ │ ├── protocols.py # typing.Protocol interfaces │ │ └── hooks.py # Hook dispatch & error isolation │ └── plugins/ │ ├── json_transform.py │ └── webhook_export.py └── tests/ └── test_plugin_engine.py ``` ## Verification Command ```bash pytest tests/test_plugin_engine.py -v --cov=plugin_engine ``` ## 100-Point Evaluation Rubric - **Protocol & Interface Design (30 pts):** Idiomatic Python Protocol specifications; strict typing. - **Dynamic Loading & Discovery (30 pts):** Clean entry-point and directory scanning via `importlib`. - **Fault Tolerance & Isolation (20 pts):** Plugin exceptions isolated with clear logging; host remains stable. - **Documentation & Reference Plugins (20 pts):** High quality `ARCHITECTURE.md` and complete reference plugins. ## Grading rubric Your submission passes when **all four** hold: 1. **Works:** Two working plugins discovered via entry-points; a crashing plugin is isolated; host never requires edits for a new plugin. 2. **Tested:** a pytest suite covers the happy path plus one failure mode, and all tests pass. 3. **Readable:** a README explains setup, the two most important commands, and one design decision you made. 4. **Production habits:** structured logging on failures and no hardcoded secrets/paths (env or config file). ## Submission contract Submit a public repo URL containing source, tests, README, and `requirements.txt` (or `pyproject.toml`). A reviewer runs your tests and two commands from your README; if either fails on a clean machine, the submission is returned with notes.