ensure_import synced the extra into a new generation and then always
raised "restart Hermes to activate", so choosing a provider whose SDK is an
opt-in extra (anthropic, bedrock, ...) failed the first message in every
fresh install or worktree even though the install had succeeded.
adopt_selected() already knows when swapping a live process onto a new
generation is safe (it was on the generation selected before the sync, and
nothing it imported changed version). Call it after the sync; raise only
when adoption was refused, naming restart_needed()'s reason.
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