piper_handler: close stdin/stdout pipes on Start() failure and on
WriteString error instead of leaking fds. Propagate WriteString error.
worker/client: log SetDeadline errors instead of discarding them.
voice/session: pushAudio marshals params inline and returns the marshal
error instead of swallowing it via mustParams (removed).
tool/matcher: log ListTools errors instead of silently returning an
empty allowlist that refuses every act.
config: applyDefaults now sets RouterThreshold and ToolTimeout defaults
so consumers self-contained defaults are belt-and-suspenders.
kami