`hermes update` runs in the pre-pull interpreter. The auto-restart phase
imports freshly-pulled gateway source, which resolves sibling imports
against the OLD sys.modules cache — so any update where an already-cached
module gained a new export ImportErrored the whole phase and left the
gateway serving pre-update code (2026-08-20 field failure: new gateway.py
needs cli_output.line_input, cached cli_output predates it).
Class fix replacing the per-symptom _UPDATE_RUNTIME_RELOAD_MODULES
approach: _purge_stale_hermes_modules() evicts every cached module under
the Hermes package prefixes (hermes_cli/gateway/tools/tui_gateway/agent)
right before the restart phase, so later lazy imports rebuild a
self-consistent module graph from the updated checkout. The updater's own
executing modules are exempt (purging them buys nothing; reload-in-place
is the unsafe op, and we never reload). Root-segment check spares
prefix-lookalike packages. Best-effort, never raises.
5 new tests incl. an end-to-end repro of the field failure shape
(stale module missing symbol -> ImportError -> purge -> import resolves).
Teknium