Munin should be two separate packages, one for master and one for the node, so that BINHOSTs can dispatch separate packages for nodes and the master. Right now each node has to install complete munin master along with all the graphing dependencies (cairo!) which is not really the Gentoo way, and requires an overlay hack to separate.
Only install munin-node and its plugins. This excludes the
scripts to generate the web pages and the graphs.
And that's the problem. If you use minimal then your package is just munin-node. If you don't, then your package is both the master and the node.
I'm talking about separation in order to have TWO distinctive packages that can be dispatched to your servers via BINHOST.
Because building everything into single package so you can have the master package brings in cairo and a plethora of other deps you don't want on thin nodes.