copies: document how 'copies' dict instances are reused
We avoid copying these instances as much as we can, so it's not
obvious what's safe to do with them. This patch tries to explain what
is safe and what is not.
Differential Revision: https://phab.mercurial-scm.org/D6578
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}