Initial project structure for MCP interceptors (#3)

Establishes a multi-language monorepo structure for MCP interceptors
with Python and TypeScript SDKs alongside the existing Go
implementation. Implements an efficient CI/CD system that only tests
what changes.


#### 🏗️ SDK Scaffolding
- **Python SDK** (`python/sdk/`): Modern Python package using
`pyproject.toml`, aligned with official MCP Python SDK patterns
- **TypeScript SDK** (`typescript/sdk/`): ESM-based package structure,
compatible with official MCP TypeScript SDK
- **Monorepo structure**: Consistent `{language}/sdk/` pattern across
all implementations
  
 #### 🚀 CI/CD Pipeline
- **Path-based workflow triggering**: Only runs CI for languages that
actually changed
    - Change Python → only Python CI runs
    - Change multiple languages → only those CIs run
- **Status check workflow**: Single required check that dynamically
validates based on changes
- **Comment triggers**: Maintainers can run all checks with `/test all`
PR comment

README.md

@@ -0,0 +1,75 @@
+# MCP Interceptors
+
+Multi-language implementations of the Model Context Protocol (MCP) interceptor framework.
+
+For the full specification and design details, see: [SEP-1763: Interceptor Framework for Model Context Protocol](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1763)
+
+## Implementations
+
+| Language | Directory | Package | Status |
+|----------|-----------|---------|--------|
+| Go | `go/sdk/` | `github.com/modelcontextprotocol/ext-interceptors/go/sdk` | Planned |
+| Python | `python/sdk/` | `mcp-ext-interceptors` | Planned |
+| TypeScript | `typescript/sdk/` | `@ext-modelcontextprotocol/interceptors` | Planned |
+
+
+## CI/CD
+
+This monorepo uses **path-based CI workflows** to efficiently test only what changes:
+
+### How It Works
+
+1. **Language-specific workflows** (`python.yml`, `go.yml`, `typescript.yml`)
+   - Only trigger when their language directory or workflow file changes
+   - Run all tests, linting, and checks for that language
+
+2. **Status check workflow** (`status-check.yml`)
+   - Runs on every PR to verify required checks passed
+   - Determines what needs to pass based on which files changed
+   - This is the only required check in branch protection
+
+### Examples
+
+- Change `python/sdk/file.py` → Only Python CI runs → PR requires Python checks to pass
+- Change both Go and TypeScript files → Both CIs run → PR requires both to pass
+- Change only `README.md` → No language CIs run → PR can merge immediately
+
+### Forcing All Checks
+
+To run all language checks regardless of changed files:
+- **In a PR**: Comment `/test all` (only works for repo owners/members/collaborators)
+- **Manually**: Use GitHub Actions UI or CLI to trigger individual workflows
+
+### Adding New Required Checks
+
+1. **Add your check** to the appropriate language workflow (e.g., `python.yml`):
+   ```yaml
+   python-security-scan:
+     name: "Security Scan"
+     runs-on: ubuntu-latest
+     steps:
+       - name: Run security checks
+         run: # your commands here
+   ```
+
+2. **Update the status check** in `.github/workflows/status-check.yml`:
+   ```javascript
+   const requiredChecks = {
+     python: [
+       'Python CI / Linting',
+       'Python CI / Unit Tests (3.10)',
+       // ... existing checks ...
+       'Python CI / Security Scan'  // ← Add your new check
+     ],
+   ```
+
+3. **Submit PR** - Your new check is now required for all relevant changes!
+
+## License
+
+Apache License 2.0 - See LICENSE file for details
+
+## Resources
+
+- [Interceptor Framework Specification (SEP-1763)](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1763) - Full specification and design details
+- [Model Context Protocol](https://modelcontextprotocol.io/specification)