An external verification run on Linux saw this test fail with a bare
`assert 'yes-deps-plugin' in []`: the install publishes into plugins/ and
a second PM admission transaction then enables it, and that admission
folds every exception into a refusal (exit 0, plugin installed but
disabled), so the assertion carried no clue about the environment-specific
cause. Verified locally that the mechanism reproduces the exact reported
shape: injecting a failure into the second sync_venv call (the enable
admission) yields the same bare failure while the first (publish) call
succeeds.
Carry the captured CLI output in the failure message so any machine that
reproduces this shows the `Enable ... refused: <cause>` line directly in
the pytest output.
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