Session files (chat, prompt, cfg, ctl, usage) now live under
s/{sid}/agent/{aid}/ instead of s/{sid}/. Add agentBase() helper
to discover the active agent directory.
resolveFullSID returned the input text as a fallback when no session
matched, causing acme built-in commands like Del to be intercepted
and passed to openChat instead of back to acme via WriteEvent.
The retry-with-remount pattern called ollie-remount (which does
sudo umount -f) from goroutines that raced with os.Exit, nuking
the shared FUSE mount. The watchdog handles recovery now.