The staleness check's bespoke mtime memo keyed only on the user
config.yaml, but load_config() merges the managed-scope config
(HERMES_MANAGED_DIR/config.yaml, /etc/hermes) whose leaf keys win. A
managed honcho.timeout with no user config.yaml made the memo cache
'no timeout' while _build resolved the managed value — the same
perpetual-rebuild mismatch this PR fixes for honcho.json. A managed
timeout edit was likewise invisible while the user file's mtime stayed
put.
load_config_readonly() is already cached on both files' signatures plus
the env-ref snapshot, so use it instead of duplicating that
invalidation logic; the defensive deepcopy the old memo existed to
avoid is skipped by the readonly variant. Drive the rebuild test
through a real config.yaml and add a HERMES_MANAGED_DIR regression
test covering stable reuse and managed-timeout edits.