New Getting Started and better TODO/placeholder/Coming Soon sections

Author: rusackas

docs/developer_portal/advanced/extension-host.md

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+---
+title: Extension Architecture
+sidebar_position: 1
+---
+
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+KIND, either express or implied.  See the License for the
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+
+# Superset Extension Architecture
+
+Apache Superset's extension architecture enables developers to enhance and customize the platform without modifying the core codebase. Inspired by the successful VS Code Extensions model, this architecture provides well-defined, versioned APIs and clear contribution points that allow the community to build upon and extend Superset's functionality.
+
+## Core Concepts
+
+### Extensions vs Plugins
+
+We use the term "extensions" rather than "plugins" to better convey the idea of enhancing and expanding Superset's core capabilities in a modular and integrated way. Extensions can add new features, modify existing behavior, and integrate deeply with the host application through well-defined APIs.
+
+### Lean Core Philosophy
+
+Superset's core remains minimal, with many features delegated to extensions. Built-in features are implemented using the same APIs available to external extension authors, ensuring consistency and validating the extension architecture through real-world usage.
+
+## Architecture Overview
+
+The extension architecture consists of several key components:
+
+### Core Packages
+
+#### @apache-superset/core (Frontend)
+Provides essential building blocks for extensions:
+- Shared UI components
+- Utility functions
+- Type definitions
+- Frontend APIs for interacting with the host
+
+#### apache-superset-core (Backend)
+Exposes backend functionality:
+- Database access APIs
+- Security models
+- REST API extensions
+- SQLAlchemy models and utilities
+
+### Extension CLI
+
+The `apache-superset-extensions-cli` package provides commands for:
+- Scaffolding new extension projects
+- Building and bundling extensions
+- Development workflows with hot-reload
+- Packaging extensions for distribution
+
+### Host Application
+
+Superset acts as the host, providing:
+- Extension registration and management
+- Dynamic loading of extension assets
+- API implementation for extensions
+- Lifecycle management (activation/deactivation)
+
+## Extension Points
+
+Extensions can contribute to various parts of Superset:
+
+### SQL Lab Extensions
+- Custom panels (left, right, bottom)
+- Editor enhancements
+- Query processors
+- Autocomplete providers
+- Execution plan visualizers
+
+### Dashboard Extensions (Future)
+- Custom widget types
+- Filter components
+- Interaction handlers
+
+### Chart Extensions (Future)
+- New visualization types
+- Data transformers
+- Export formats
+
+## Technical Foundation
+
+### Module Federation
+
+Frontend extensions leverage Webpack Module Federation for dynamic loading:
+- Extensions are built independently
+- Dependencies are shared with the host
+- No rebuild of Superset required
+- Runtime loading of extension assets
+
+### API Versioning
+
+All public APIs follow semantic versioning:
+- Breaking changes require major version bumps
+- Extensions declare compatibility requirements
+- Backward compatibility maintained within major versions
+
+### Security Model
+
+- Extensions disabled by default (require `ENABLE_EXTENSIONS` flag)
+- Built-in extensions follow same security standards as core
+- External extensions run in same context as host (sandboxing planned)
+- Administrators responsible for vetting third-party extensions
+
+## Development Workflow
+
+1. **Initialize**: Use CLI to scaffold new extension
+2. **Develop**: Work with hot-reload in development mode
+3. **Build**: Bundle frontend and backend assets
+4. **Package**: Create `.supx` distribution file
+5. **Deploy**: Upload through API or management UI
+
+## Example: Dataset References Extension
+
+A practical example demonstrating the architecture:
+
+```typescript
+// Frontend activation
+export function activate(context) {
+  // Register a new SQL Lab panel
+  const panel = core.registerView('dataset_references.main',
+    <DatasetReferencesPanel />
+  );
+
+  // Listen to query changes
+  const listener = sqlLab.onDidQueryRun(editor => {
+    // Analyze query and update panel
+  });
+
+  // Cleanup on deactivation
+  context.subscriptions.push(panel, listener);
+}
+```
+
+```python
+# Backend API extension
+from superset_core.api import rest_api
+from .api import DatasetReferencesAPI
+
+# Register custom REST endpoints
+rest_api.add_extension_api(DatasetReferencesAPI)
+```
+
+## Best Practices
+
+### Extension Design
+- Keep extensions focused on specific functionality
+- Use versioned APIs for stability
+- Handle cleanup properly on deactivation
+- Follow Superset's coding standards
+
+### Performance
+- Lazy load assets when possible
+- Minimize bundle sizes
+- Share dependencies with host
+- Cache expensive operations
+
+### Compatibility
+- Declare API version requirements
+- Test across Superset versions
+- Provide migration guides for breaking changes
+- Document compatibility clearly
+
+## Future Roadmap
+
+Planned enhancements include:
+- JavaScript sandboxing for untrusted extensions
+- Extension marketplace and registry
+- Inter-extension communication
+- Advanced theming capabilities
+- Backend hot-reload without restart
+
+## Getting Started
+
+Ready to build your first extension? Check out:
+- [Extension Development Guide](/developer_portal/get-started/your-first-extension)
+- [API Reference](/developer_portal/api/frontend)
+- [CLI Documentation](/developer_portal/cli/overview)
+- [Example Extensions](/developer_portal/examples)