Summary

Implements the suggestion in #3238: re-export the HTTP-client helpers from a public module so that customizing the streamable-HTTP client (headers/auth/timeout) no longer requires importing the private mcp.shared._httpx_utils.

Since 2.0 removed the headers/timeout/auth kwargs from streamable_http_client, the only supported way to build a conforming httpx2.AsyncClient is create_mcp_http_client — but it, the McpHttpClientFactory protocol, and the default-timeout constants were only reachable via the private module.

Changes

• src/mcp/client/streamable_http.py — re-export create_mcp_http_client, McpHttpClientFactory, MCP_DEFAULT_TIMEOUT, and MCP_DEFAULT_SSE_READ_TIMEOUT from the same module that already exposes streamable_http_client, and add a module-level __all__ declaring the public surface. The redundant-alias / __all__ forms keep this a pure re-export (no behavior change) and satisfy ruff's F401.
• tests/shared/test_httpx_utils.py — new test_public_reexport_from_streamable_http asserting the public names resolve to the same objects as the private ones.
• docs/migration.md — point the "build the http_client" guidance at the public import path, with an example.

Notes

• This is intentionally additive: nothing is removed or renamed, the private module still works, and existing imports are unaffected. No external code uses import * from this module (tests import names explicitly), so adding __all__ does not change any current consumer.
• I scoped the re-export to mcp.client.streamable_http (rather than a broader mcp.shared) because that's where streamable_http_client lives and where McpHttpClientFactory was importable from in 1.x — happy to also/instead export from elsewhere if you'd prefer a different home.

Fixes #3238

Testing

• tests/shared/test_httpx_utils.py — 3 passed (2 pre-existing + 1 new).
• ruff check and ruff format --check clean on the changed files.