profile_env_for_background_worker mirrored the profile home into process-global
os.environ["HERMES_HOME"] and yielded the worker body OUTSIDE the setup lock, so a
concurrent cross-profile worker (e.g. background title generation on another
profile) could clobber os.environ mid-body — the agent config reader then resolved
the WRONG profile's config (intermittent turn-init failures citing an unused
provider; b3nw's v0.51.849 repro). Now installs hermes-agent v0.18.0's
context-local home override (set_hermes_home_override, a ContextVar that
get_hermes_home() consults before os.environ) for the resolved non-default profile
home — set before yield, reset in finally — so a config read in the worker body
resolves THIS profile's home from task-local state, immune to a concurrent
os.environ clobber. No worker serialization, no os.environ mutation, no detection
heuristic (both earlier WebUI-only mitigations were rejected as regression-unsafe).
Graceful degradation: the override module is resolved lazily+optionally
(_resolve_hermes_home_override, mirroring _resolve_secret_scope_module). On agents
< v0.18.0 the symbol is absent -> returns None -> pre-existing os.environ-mirror
behavior unchanged (no regression, no new failure mode).
Self-built (nesquena-hermes); nesquena independent review APPROVED.
