Use when adding or modifying frontend UI components — interactive overlays for WaitingFor states, game board elements, card choice modals, animation effects, or any React component that interfaces with the engine via GameAction dispatch.
Use to run a continuous review sweep over open contributor PRs in phase.rs. The skill is a thin orchestration layer over scripts/pr_review.py: discover candidates, detect stale reviews/follow-ups, dispatch review-impl for PRs that need judgment, and delegate authorized merge handling to pr-contribution-handler.
Use when adding or modifying replacement effects — ETB-tapped, shock lands, damage prevention, "as enters" choices, or any event-modifying ability. Covers ReplacementDefinition wiring, the pipeline flow, post-replacement effects, and interactive pre-zone-change choices.
Use when adding a new effect, mechanic, or parser capability to the engine. Covers the full lifecycle from types → parser → resolver → targeting → frontend → AI → tests.
Use when adding or modifying keyword abilities — evergreen keywords (flying, trample), parameterized keywords (ward {2}, kicker {R}), protection variants, or any keyword that needs runtime behavior wired into combat, targeting, damage, or triggers.
Use when adding or modifying static abilities, continuous effects, or layer system modifications — type-changing effects, power/toughness modification, keyword granting, color changes, CDAs, or any "as long as" / "enchanted creature" / "creatures you control" ability.
Use when adding or modifying triggered abilities — ETB, dies, attacks, damage dealt, spell cast, phase-based, or any "When/Whenever/At the beginning of" ability. Covers TriggerDefinition, TriggerMode, the matcher registry, APNAP ordering, targeting, intervening-if, constraints, and parser wiring.
Canonical recipe for writing engine cast-pipeline tests. Use GameScenario + GameRunner::cast(...).resolve() and assert via CastOutcome deltas. Covers the six test-harness foot-guns (hand-written TargetRef vectors, incomplete modal target submission, wrong-point hand baseline, inline-keyword cards, AST-internal flag assertions, vacuous negative assertions) and the right-way fix for each. Use whenever writing or porting a runtime test that casts a spell and checks its effect.