Build stdio MCP Server Exposing fetch Stripe invoice for VS Code with MCP extension

You are a senior agent engineer building a production-grade Model Context Protocol (MCP) server.

**Goal:** Expose "fetch Stripe invoice" as a callable MCP tool that is reachable from VS Code with MCP extension over the stdio transport. Runtime: TypeScript + Node 20. Auth: mTLS. Schema validator: Zod.

## Deliverables

1. **Project scaffold** — complete file tree with:
   - `package.json` / `pyproject.toml` with pinned deps (`@modelcontextprotocol/sdk` or `mcp` Python SDK)
   - `src/server.ts` or `src/server.py` entrypoint
   - `src/tools/fetch Stripe invoice.ts` tool implementation
   - `src/auth.ts` auth middleware
   - `tests/` folder with unit + integration tests
   - `Dockerfile` and `README.md`

2. **Tool schema** — write the exact Zod schema for:
   - Inputs (with descriptions, examples, enum constraints where relevant)
   - Outputs (typed, not free-form strings)
   - Derive the JSON Schema the MCP SDK will advertise to clients

3. **Transport setup for stdio**
   - If stdio: how to wire stdin/stdout, flush buffers, handle SIGTERM
   - If SSE: `/sse` endpoint, `POST /message` for client→server, session ID correlation
   - If HTTP streaming / Streamable HTTP: single endpoint, `Mcp-Session-Id` header, resumability
   - If WebSocket: frame handling, ping/pong, reconnection

4. **Authentication (mTLS)** — justify this choice for this tool and implement:
   - Where credentials live (env var, OAuth token store, keychain)
   - Refresh / rotation strategy
   - Failure mode when auth expires mid-session
   - Redaction in logs

5. **Error handling** — handle each of:
   - Invalid input (return `isError: true` with actionable message, never throw)
   - Upstream service failure (retry with backoff; surface which downstream failed)
   - Timeout (set a hard deadline, cancel in-flight work)
   - Permission denied (never leak why in prod; log full reason server-side)
   - Rate limiting (respect Retry-After, queue vs. reject)

6. **Example client flow**
   - How VS Code with MCP extension discovers this tool via `tools/list`
   - A sample `tools/call` request + response JSON
   - What the user types in VS Code with MCP extension to trigger it
   - How the tool result is rendered back to the model

7. **Host-specific install instructions for VS Code with MCP extension**
   - Exact config file path (e.g. `~/Library/Application Support/Claude/claude_desktop_config.json` for Claude Desktop, `~/.cursor/mcp.json` for Cursor, `.mcp.json` at repo root for Claude Code)
   - The JSON block to paste in, with all required env vars
   - How to verify the server connected (log lines to look for, UI indicator)
   - Common gotchas specific to VS Code with MCP extension

8. **Test harness**
   - Unit tests for the tool handler in isolation (mock the upstream)
   - Integration test that spawns the server and drives it via the MCP SDK client
   - Manual smoke test checklist for VS Code with MCP extension

9. **Observability**
   - Structured logging (request ID, tool name, duration, outcome)
   - Metrics counter (calls, errors, p95 latency)
   - How to tail logs when running under VS Code with MCP extension

10. **Production hardening**
    - Resource limits (max concurrent calls, max payload size)
    - Graceful shutdown
    - Secret rotation without restart
    - Security review checklist (injection, SSRF, path traversal for file tools)

Write real, copy-pasteable code for the server entrypoint, the tool schema, and the auth middleware. No pseudocode. Treat this as a PR-ready implementation.