The HTTP entry point: routes paths to YmerNode.Mcp, and answers 404 to everything else.

It exists because the two halves it joins each decline the job. Bandit serves one plug and does no path matching, and YmerNode.Mcp — a Wymcp.Router mount — reads no path at all: it is built to be forwarded to, so a mount wired straight into Bandit would answer MCP on every path, / included. Neither is wrong; they just leave the /mcp in this node's documented address unowned. This module owns it, and is the whole of what a Phoenix app would get from its endpoint and router.

The catch-all 404 is deliberate rather than incidental: the node serves exactly one path, so anything else is a client misconfiguration, and saying so plainly beats handing an MCP session to a caller who asked for something else.