Every line still promising that `gateway.multiplex_profiles: false` keeps
per-profile gateways, or documenting the deleted `migrate --standalone`
rollback, now describes the shipped behaviour: one gateway per host serves
every profile; `false` no-ops with a warning; `hermes update` folds a fleet
unless a real boundary (different UNIX user, HERMES_HOME outside profiles/)
holds; a blocked fleet keeps `--force` per profile; re-running
`migrate --multiplex` converges a half-migrated host; a manifest on disk is the
resume record, never a rollback. Adds the new "No new per-profile gateways"
section with the exact refusal `hermes -p <name> gateway install` prints.
Files: website/docs/user-guide/multi-profile-gateways.md,
website/docs/reference/cli-commands.md (migrate row),
website/docs/developer-guide/multiplexing-gateway.md (eager activation no
longer honours `false`), hermes_cli/AGENTS.md (migrate + refusal seams).
Completes #118273 (docs item). Part of #109417
91d1339a8d