Server→client stream channel (streamable HTTP — the ONLY transport).

⚠️ Do NOT turn the bare GET into an error. Measured findings from the 2026-07-10 migration — 勿凭直觉推翻:

Captured from real mcp-remote: probe GET accept: application/json, text/event-stream server→client GET MCP-Protocol-Version: 2025-06-18, accept: text/event-stream legacy SSE GET accept: text/event-stream (no version header)

A streamable-HTTP client GETs this URL twice (probe, then the optional server→client stream) and one of those GETs is header-identical to a legacy client's: accept: text/event-stream, no version header. Headers CANNOT decide who is asking. And answering ANY error is worse: mcp-remote's shouldFallbackOnError matches "404"/"405" in the error string and permanently abandons streamable HTTP. So EVERY bare GET receives a valid but EMPTY stream (keepalives + a tools/list_changed nudge; no registry entry, no fd tracked).

Only the explicit ?transport=sse opt-in — the sole path that ever received the legacy endpoint handshake — is retired: 410 Gone since 2026-07-28.