#4654 swamp extension update writes an upgraded extension's skills into a skill directory another extension owns

swamp extension update installs each upgrade with force, so the skill-directory conflict check that a direct pull runs is skipped. When the new version of an extension ships a skill whose name matches a skill directory another installed extension owns (for example both ship myskill), the update writes into that directory and records the file as the upgraded extension's. Running swamp extension rm on the upgraded extension afterwards deletes the whole skill directory, so the other extension loses its skill.

A direct swamp extension pull of the same version reports that the skill directory already exists and asks before writing (or needs --yes).

Expected: update does not write into a skill directory that another extension's lockfile entry claims; it reports the extension as not updated (or asks, in an interactive terminal), as pull does.

Found while reviewing dependency upgrades for swamp-club#4634, where pull's dependency upgrades now ask instead of forcing; update keeps its replace-in-place behaviour, so this case remains there.