The comment-keeping summer.yaml edit refused a flow-style plugins list
(plugins: [{id: a, module: b}]) that plugin:add used to handle with a
full rewrite. The edit now replaces an inline list, over one or several
lines, with a block list of its items plus the new ones and keeps every
other line. A list it cannot edit in place (a tagged one, say) falls
back to the full SaveManifest rewrite with a note that the comments were
not kept. plugin:install gets the same behaviour.
e6b3aa2222