Sessions that never ran a terminal command (MCP-only, cron, gateway)
have no active sandbox environment, so maybe_persist_tool_result()
got env=None and fell through to the inline-truncate fallback --
a 467K MCP result was cut to a ~1.3K preview with no file written
('Full output could not be saved to sandbox').
Now the host-side cases (env=None or the local backend) write the
spill file directly to $HERMES_HOME/cache/spillover/<id>.txt,
alongside the other Hermes-owned caches instead of littering /tmp.
Remote backends (docker/ssh/modal/daytona) keep the in-sandbox
env.execute() write since read_file resolves in-sandbox there.
Cleanup: the gateway housekeeping loop prunes spillover hourly with
the other media caches, and a once-per-process best-effort prune on
first spill covers CLI-only installs.
c91681c69a