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12-task TDD plan in two increments: - Increment 1 (Tasks 1-5): announce-all-to-both + capture tally. - Increment 2 (Tasks 6-11): client-local phantom opponent-piece layer. Each task has exact files, complete code, and verification commands. Server/shared tasks are TDD'd with vitest; client tasks use svelte-check plus manual verification (no client test harness, by design). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>