Fix Trade Caravan

[keloide]

Summary

Trade Caravan's activated ability Remove two currency counters from ~: Untap target basic land. Activate only during an opponent's upkeep. dropped its timing restriction to Effect::Unimplemented, leaving the ability activatable at any time. parse_activation_during_role_gate handled during an opponent's turn and during your upkeep but had no arm for during an opponent's upkeep. This adds that arm by composing existing building blocks rather than proliferating a new DuringOpponents* restriction sibling.

Implementation method (required)

Method: /engine-implementer (gates applied inline: add-engine-variant existence/parameterization/boundary gate + mandatory final review-impl)

CR references

• CR 503.1 — the upkeep step (new ParsedCondition::IsDuringUpkeep predicate + its evaluator arm).
• CR 102.1 — the active player is the player whose turn it is (opponent scope via Not(IsYourTurn)).
• CR 602.5b — an activated ability's use restriction persists across control changes.

All three grep-verified against docs/MagicCompRules.txt.

Design

Rather than add a DuringOpponentsUpkeep sibling to ActivationRestriction (which already expresses opponent-turn scope via RequiresCondition { Not(IsYourTurn) }, not a dedicated DuringOpponentsTurn variant), the fix composes:

• ParsedCondition::IsDuringUpkeep — a scope-free upkeep-step predicate, orthogonal to every existing ParsedCondition variant (there was no prior phase predicate).
• during an opponent's upkeep → RequiresCondition { And([Not(IsYourTurn), IsDuringUpkeep]) }, reusing the same opponent-turn composition idiom as the existing bare opponent-turn gate.

add-engine-variant gate result for ParsedCondition::IsDuringUpkeep: Stage 1 DOES_NOT_EXIST (no phase predicate in ParsedCondition), Stage 2 EXTEND_OK (orthogonal — not a sibling cluster), Stage 3 WITHIN_SECTION (CR 503, upkeep step).

Verification

• Required checks ran clean, or the exact CI-owned alternative is stated below.

• Gate A output below is for the current committed head.

• Final review-impl below is clean for the current committed head.

• Both anchors cite existing analogous code at the same seam.

• cargo fmt --all — clean.

• cargo clippy -p engine --all-targets -- -D warnings — clean, 0 warnings (full compile; confirms every exhaustive ParsedCondition match is satisfied).

• cargo test -p engine --lib — ok. 17440 passed; 0 failed; 6 ignored.

• cargo test -p engine --test integration — ok. 3676 passed; 0 failed; 2 ignored.

• New tests: activated_ability_opponents_upkeep_restriction_composes_scope_and_step (parser building block, drives production parse(), asserts composed restriction + zero Effect::Unimplemented) and opponents_upkeep_activation_condition_gates_on_step_and_scope (runtime, drives real evaluate_condition across the full turn-scope × step matrix) — both pass.

• cargo coverage / cargo semantic-audit — deferred to CI: both require a full MTGJSON card-data.json export (156 MB+ multi-request per-set fetch) that isn't feasible in this environment (only a test fixture is present locally). Direct evidence instead: the parsed AST for Trade Caravan now contains zero Effect::Unimplemented and the correct RequiresCondition { And([Not(IsYourTurn), IsDuringUpkeep]) } restriction. Since card_face_has_unimplemented_parts (game/coverage.rs) derives supported precisely from the absence of Unimplemented parts, Trade Caravan is now supported: true, gap_count: 0.

Gate A

Gate A PASS head=c5024c97678be3ffdcbac252e235cd8ed145fdab base=ee061e5c7485619644dc6089976b94a1d29a0202

Anchored on

• crates/engine/src/parser/oracle.rs:6792 — value(opponents_turn_activation_restriction(), alt((tag("during an opponent's turn"), tag("during an opponents turn")))): the same value(computed_restriction, alt((tag, tag))) during-role arm the new opponent's-upkeep arm mirrors (combinator family, naming, placement).
• crates/engine/src/parser/oracle.rs:6803 — value(ActivationRestriction::DuringYourUpkeep, alt((tag("during your upkeep"), tag("during their upkeep")))): the sibling upkeep-step during-role arm, immediately adjacent, establishing the apostrophe/possessive variant pattern reused verbatim.
• (supporting) crates/engine/src/game/restrictions.rs:1520 ParsedCondition::IsYourTurn => state.active_player == player and restrictions.rs:1066 CastingRestriction::DuringOpponentsUpkeep => state.active_player != player && state.phase == Phase::Upkeep — the evaluator arms the new IsDuringUpkeep => state.phase == Phase::Upkeep arm mirrors.

Final review-impl

Final review-impl PASS head=c5024c97678be3ffdcbac252e235cd8ed145fdab

Claimed parse impact

• Trade Caravan (removed from docs/parser-misparse-backlog.md root cause 28)

🤖 Generated with Claude Code

---

Generated by Claude Code

[github-actions]

Parse changes introduced by this PR · 3 card(s), 4 signature(s) (baseline: main ee061e5c7485)

🟢 Added (1 signature)

• 1 card · ➕ ability/where_x_binding · added: where_x_binding
  • Affected (first 3): Kotis, the Fangkeeper

🔴 Removed (2 signatures)

• 1 card · ➖ ability/CastFromZone · removed: CastFromZone (free cast=yes, target=cards exiled by source)
  • Affected (first 3): Kotis, the Fangkeeper
• 1 card · ➖ ability/activate · removed: activate
  • Affected (first 3): Trade Caravan

🟡 Modified fields (1 signature)

• 1 card · 🔄 trigger/DamageDone · changed field valid target: ∅ → blocking creature
  • Affected (first 3): Kusari-Gama

8 card(s) had Oracle-text changes (errata/reprint) — excluded as non-parser.
New cards in head: 4.
Cards only in baseline: 2.