App MCP endpoint

Every tenant host is an MCP server (streamable HTTP, single JSON-RPC responses): initialize, ping, tools/list, tools/call. Tools are the live release's routed functions that export a static tool declaration; a call is a POST to the tool's route. Ungated tools need no token; a gated call without a valid Authorization: Bearer access token answers 401 with WWW-Authenticate: Bearer resource_metadata=…, scope="tools". Cookies never authenticate; a cross-origin request is refused. A body of only notifications is accepted with 202 and no body.