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Validate(root): optional startup/test check for tree authoring faults — >1 slot child per node, empty word, duplicate sibling words, dead-end node — traversing circular slots without looping (#3). keypress subpackage: WaitForKey(ctx, cancel) cancels a context on any keystroke for watch-style streaming commands, with per-GOOS cbreak (linux TCGETS/TCSETS, BSD TIOCGETA/TIOCSETA) and a non-tty/unsupported fallback that just waits on ctx. Lifts the last OpenBSD-specific bit out of evpnc/maglevc's watch.go (#6). docs: replace PROPOSAL.md with an RFC-2119 design.md (FR/NFR for the library). Example now dogfoods Validate (a unit test) and keypress (a bounded `watch` command). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>