Add Necropotence

[bruno-branco-brito]

Summary

Adds engine support for Necropotence and the broader face-down-exile class (Bomat Courier, Asmodeus the Archfiend, Knowledge Vault).

Files changed

• crates/engine/src/game/effects/exile_top.rs
• crates/engine/src/game/effects/mod.rs
• crates/engine/src/game/effects/deal_damage.rs
• crates/engine/src/game/coverage.rs
• crates/engine/src/game/dungeon.rs
• crates/engine/src/game/visibility.rs
• crates/engine/src/parser/oracle_effect/mod.rs
• crates/engine/src/parser/oracle_effect/imperative.rs
• crates/engine/src/parser/oracle_ir/ast.rs
• crates/engine/src/parser/oracle_trigger.rs
• crates/engine/src/parser/oracle_replacement.rs
• crates/engine/src/parser/oracle.rs
• crates/engine/src/parser/oracle_ir/snapshots/...__bomat_courier_ir.snap
• crates/engine/src/parser/oracle_ir/snapshots/...__bomat_courier_lowered.snap
• crates/engine/src/types/ability.rs
• crates/mtgish-import/src/convert/action.rs

CR references

• CR 406.1 — exile zone is a holding area for objects (authorizing reference for treating ExileTop as destination=Exile for tracked-set chain assembly).
• CR 406.3 — a card exiled face down can't be examined by any player except when instructions allow it (authorizing rule for the new Effect::ExileTop { face_down: true } redaction path).
• CR 603.7 — effects may create delayed triggered abilities (authorizing rule for the recall delayed-trigger pathway).
• CR 603.7c — delayed triggered abilities that refer to a particular object (authorizing rule for tracked-set object binding).
• CR 701.9 — Discard (authorizing rule for the on-discard trigger event).

(CR 614.10 / CR 614.1b already implement the "Skip your draw step." static-ability piece via StaticMode::SkipStep { step: Phase::Draw } — not modified by this PR.)

Review round 2 — gemini-code-assist findings addressed

• HIGH (face-down fidelity, CR 406.3 / Rule R17): Effect::ExileTop is now parameterized with a face_down field. The imperative parser strips a trailing "face down" qualifier via a new strip_exile_top_face_down helper (nom tag for dispatch, post-tag char-boundary check), threading the bool through ZoneCounterImperativeAst::ExileTop into the lowered effect. The resolver flips obj.face_down after move_to_zone (foretell pattern). visibility.rs generalizes the prior foretold-only filter so every face-down card in Exile is redacted for non-owner viewers via hide_card. New resolver tests (exile_top_face_down_sets_object_face_down_flag, face-up counter-test) and a parser test (exile_top_card_of_your_library_face_down_parses_with_face_down_true) cover the new behavior; Bomat Courier IR + lowered snapshots refreshed to show face_down: true. The field uses #[serde(default, skip_serializing_if = "std::ops::Not::not")] so existing JSON card-data for face-up exiles is byte-identical.
• MED (im::Vector for tracked-set buildup, Rule R7): Resolved by eliminating the local collection altogether — the generic chain processor in effects::resolve_ability_chain already publishes ExileTop's affected ids via affected_objects_from_events (mapped to the Exile destination zone), so the resolver no longer maintains its own buffer. This also fixes a pre-existing double-publish that surfaced as a regression in compound_zone_change_chain_unifies_tracked_set (lib_card was receiving two PlayFromExile grants because both the leaf resolver and the chain processor were publishing). The publishing-side test exile_top_publishes_tracked_set_when_followed_by_recall_delayed_trigger now drives through effects::resolve_ability_chain so the chain-layer publish runs in test as it does in live game resolution.

Track

Non-developer

LLM

Model: claude-opus-4-7
Thinking: medium

Verification

Local verification skipped — see CI status checks.

Validation Failures

None.

CI Failures

None.

[gemini-code-assist]

Code Review

This pull request updates the ExileTop effect to support publishing tracked sets, enabling downstream delayed triggers (like Necropotence's end-step recall) to correctly reference exiled cards. It also includes parser tests for discard-to-exile triggers and adjusts the visibility of the next_sub_needs_tracked_set helper. Feedback indicates that the implementation currently lacks support for face-down exile, violating CR 406.3 and Rule R17 regarding hidden information integrity. Additionally, the use of a standard Vec for collecting exiled IDs violates Rule R7, which requires persistent data structures (im::Vector) for GameState collections to maintain efficient structural sharing.