Phase 6 part 4b (partial):
- GameMode::Challenge variant in solitaire_core. undo() returns
RuleViolation when mode is Challenge so the player commits to each
decision.
- solitaire_data::challenge defines a stable CHALLENGE_SEEDS list with
challenge_seed_for(index) wrapping modulo length.
- PlayerProgress.challenge_index (serde-default for older saves) tracks
how far the player has progressed.
- ChallengePlugin advances the cursor on Challenge-mode wins, persists,
and emits ChallengeAdvancedEvent. Pressing X starts a Challenge-mode
game with the current seed; gated to level >= CHALLENGE_UNLOCK_LEVEL (5).
- InputPlugin's Z key (Zen mode) is now also gated to level >= 5.
Time Attack and unlock UI still deferred.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
funman300
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