Allow to connect to ChatGPT custom MCP connectors over SSE

[delebedev]

Allow this MCP server to connect to ChatGPT’s Custom MCP Connectors over SSE.

• Added SSE/streamable transport selection controlled by MCP_TRANSPORT, including lazy client reuse so repeated SSE calls stay stable.
• Documented how to run the server for ChatGPT, including env vars and tunneling via ngrok.

Test with ChatGPT

Sanity check with Claude after changes

[Copilot]

Pull Request Overview

This PR enables the MCP server to connect with ChatGPT's custom MCP connectors over SSE transport, in addition to the existing stdio transport for Claude Desktop. The implementation handles httpx client lifecycle issues that arise when connections are severed between tool invocations.

Key changes:

• Added lazy initialization and automatic recreation of the httpx AsyncClient to handle client closures
• Implemented transport selection via MCP_TRANSPORT environment variable (stdio, sse, streamable-http)
• Added ChatGPT-specific usage documentation with SSE setup instructions

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/intervals_mcp_server/server.py	Implements lazy httpx client initialization with closure detection, adds transport selection logic, and refactors request handling to support retry on client closure
tests/test_make_intervals_request.py	Updates MockAsyncClient to track closure state for testing the new client lifecycle management
README.md	Adds ChatGPT usage section with SSE transport configuration instructions

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[Copilot]

After recreating httpx_client, the new instance should be assigned back to the global variable before calling _send_request. The current code creates a new client but _send_request still receives the locally scoped httpx_client rather than ensuring the global reference is updated. Consider using client = await _get_httpx_client() instead to maintain consistency with the retry pattern.

Suggested change

	response = await _send_request(httpx_client)
	client = await _get_httpx_client()
	response = await _send_request(client)