Fixes#25: on Windows the stdin 'end' event never fires for hook
subprocesses, hanging every hook for its full timeout. readStdin now
parses incrementally and resolves as soon as the payload is complete
JSON, with a 3s fallback timer — the same pattern the statusline
renderer already used. Also drops dead formatRelativeTime code.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>