Investigate Streamable HTTP transport for ncp-mcp-server

[madeinplutofabio]

Summary

ncp-mcp-server v0 ships stdio transport only. Sufficient for local MCP-compatible hosts. Streamable HTTP (the transport that replaced legacy HTTP+SSE in the current MCP spec) matters for server or web deployments where the adapter runs as a remote service the host connects to.

Acceptance criteria (investigation only, no implementation)

• Confirm the current MCP Streamable HTTP requirements against the latest spec.
• Evaluate rmcp support for Streamable HTTP (which features, what is stable).
• Propose a CLI shape, for example --transport stdio|http (default stdio for backwards compat).
• Define security defaults: bind address (loopback by default? configurable?), auth assumptions, CORS posture.
• Decide whether --transport http should require an explicit --bind-addr or default to 127.0.0.1:<port>.
• No implementation required in this issue unless the design is accepted and lands as a follow-up PR.

Why this is research, not implementation

docs/MCP_ADAPTER.md §1 deferred Streamable HTTP to a future release pending the MCP spec settling and adopter demand surfacing. This issue surfaces the demand-gathering investigation. It does NOT commit to implementation.

Where to read

• docs/MCP_ADAPTER.md §1 (Scope) and §4 (current transport posture)
• rmcp crate documentation for transport options
• MCP spec: Streamable HTTP transport section