An update disabled any plugin that failed a trial build or its
requires_hermes check. Both can be about us, not the plugin: an untagged
source checkout reads as an older release (#122054), so requires_hermes
misjudges a fine plugin, and a download failure says nothing about the
plugin's code. Those now sit the plugin out of the build: config stays
untouched and it rejoins once the cause clears.
Disabling still happens on evidence about the plugin: requires-python vs
the pinned interpreter, manifest_version, an invalid declaration, a uv
resolution conflict, or its own build backend failing (new BuildFailure,
keyed on uv's 'The build backend returned an error').
enabled_member_dirs now skips a requires_hermes misfit instead of
raising. Boot's currency check raised on it before any sync could run, so
the launch path never reached the update sync. The loader skips such a
plugin anyway; admission still refuses enabling one.
c500ee8771