Implement Opponent Discards Effect in Engine

Summary

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Session command

Read docs/work-queue.md and do the next unchecked batch. For each batch:

Read the engine files (mtg-engine/src/abilities.rs, mtg-engine/src/game.rs) to understand current Effect/StaticEffect variants
If the batch has a NOTE about uncertainty, investigate first and update the queue with findings before committing the fix
If engine work is needed: add the variant, constructor, and match arm, and look for the Java implementation to see the bigger picture
Add a test for any new engine effect (follow the pattern in game.rs mod tests)
Fix all cards listed in the batch (grep to find exact lines, fix across all 4 set files)
cargo check -p mtg-cards && cargo test --lib
Update docs: mark cards in docs/{fdn,tla,tdm,ecl}-remediation.md, update ROADMAP.md
Check off the batch in docs/work-queue.md with today's date
If you discover new cards that fit the current or a future batch while working, add them to the queue

If a batch turns out to be wrong or more complex than described, update the queue with what you learned and move on to the next one.

I'll start by reading the work queue to find the next unchecked batch.

Next batch is Batch 3: OpponentDiscards. Let me read the engine files and find the affected cards.

Let me read the relevant parts of game.rs and find the cards.

1013-                    // SelectedTargets for proper player targeting)
1014-                    if let Some(player) = self.state.players.get_mut(&controller) {
1015-                        player.life -= *amount as i32;
1016-                    }
1017-                }
1018:                Effect::LoseLifeOpponents { amount } => {
1019-                    let opponents: Vec<PlayerId> = self.state.turn_order.iter()
1020-                        .filter(|&&id| id != controller)
1021-                        .copied()
1022-                        .collect();
1023-                    for opp in opponents {

mtg-rl/mtg-cards/src/sets/fdn.rs:616:                "When Burglar Rat enters, each opponent discards a card.",
mtg-rl/mtg-cards/src/sets/fdn.rs:617:                vec![Effect::Custom("Each opponent discards a card.".into())],
mtg-rl/mtg-cards/src/sets/fdn.rs:5338:                "When this creature enters, each opponent discards a card and loses 2 life. You draw a card and gain 2 life.",
mtg-rl/mtg-cards/src/sets/fdn.rs:5340:                vec![Effect::Custom("When this creature enters, each opponent discards a card and loses 2 life. You draw a card and gain 2 life.".into())],
mtg-rl/mtg-cards/src/sets/fdn.rs:5518:                "When this creature enters, if an opponent lost life this turn, each opponent discards a card.",
mtg-rl/mtg-cards/src/sets/fdn.rs:5520:                vec![Effect::Custom("When this creature enters, if an opponent lost life this turn, each opponent discards a card.".into())],
mtg-rl/mtg-cards/src/sets/ecl.rs:595:                "When Dream Seizer enters, put a -1/-1 counter on it. When you do, each opponent discards a card.",
mtg-rl/mtg-cards/src/sets/ecl.rs:596:                vec![Effect::Custom("Put a -1/-1 counter on Dream Seizer. Each opponent discards a card.".into())],
mtg-rl/mtg-cards/src/sets/ecl.rs:2031:    // Sorcery for {1}{B}. Choose one: opponent discards nonland permanent card; or target creature gets -2/-2 until EOT.

1094-                Effect::AddMana { mana } => {
1095-                    if let Some(player) = self.state.players.get_mut(&controller) {
1096-                        player.mana_pool.add(*mana, None, false);
1097-                    }
1098-                }
1099:                Effect::DiscardCards { count } => {
1100-                    / Controller discards (simplified: discard from the back of hand)
1101-                    let hand: Vec<ObjectId> = self.state.players.get(&controller)
1102-                        .map(|p| p.hand.iter().copied().collect())
1103-                        .unwrap_or_default();
1104-                    let view = crate::decision::GameView::placeholder();

Let me read the DiscardCards implementation and the cards in more detail.

Now I have a clear picture. I need to:

Add Effect::DiscardOpponents { count: u32 } variant to the Effect enum in abilities.rs
Add a constructor Effect::discard_opponents(count)
Add the match arm in game.rs execute_effects
Add a test in game.rs
Fix the cards:
- FDN: Burglar Rat (line 617) - simple swap
- FDN: Arbiter of Woe (line 5340) - compound: opponent discards + loses 2 life + you draw + gain 2 life
- FDN: Bloodtithe Collector (line 5520) - conditional, may be harder (keep as Custom with note)
- ECL: Dream Seizer (line 596) - compound: self -1/-1 counter + opponent discards

Now I need to look at how the execute_effects match is structured to find where to add the new arm, and then check the test patterns in game.rs.

Now let me find the end of the execute_effects match and the test section in game.rs.

429-                    perm.granted_keywords = crate::constants::KeywordAbilities::empty();
430-                    perm.removed_keywords = crate::constants::KeywordAbilities::empty();
431-                    // Remove "can't block" sentinel counters
432:                    perm.counters.remove_all(&crate::counters::CounterType::Custom("cant_block".into()));
433-                }
434-                // Empty mana pools
435-                for player in self.state.players.values_mut() {
--
1240-                    for &target_id in targets {
1241-                        if let Some(perm) = self.state.battlefield.get_mut(target_id) {
1242-                            // Use a sentinel counter to indicate can't block
1243:                            perm.add_counters(crate::counters::CounterType::Custom("cant_block".into()), 1);
1244-                        }
1245-                    }
1246-                }

Good. Now I have all the context I need. Let me implement the batch:

Add Effect::DiscardOpponents { count } variant + constructor + match arm in game.rs
Add a test
Fix the cards

Let me start with the engine changes.

Now add the constructor in the Effect impl block:

Now add the match arm in game.rs. Let me add it right after the existing DiscardCards handler:

Now add a test. Let me append it before the closing } of the tests module:

Now let me verify the engine compiles and the test passes:

>cd /mnt/dest-btrfs/home/jc/src/mage/mtg-rl && cargo test --lib -p mtg-engine -- discard_opponents_effect 2>&1

Exit code 101
   Compiling mtg-engine v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-engine)
error[E0609]: no field `cards` on type `state::GameState`
    --> mtg-engine/src/game.rs:2379:20
     |
2379 |         game.state.cards.insert(c1_id, card1);
     |                    ^^^^^ unknown field
     |
     = note: available fields are: `players`, `turn_order`, `battlefield`, `stack`, `exile` ... and 17 others

error[E0609]: no field `cards` on type `state::GameState`
    --> mtg-engine/src/game.rs:2380:20
     |
2380 |         game.state.cards.insert(c2_id, card2);
     |                    ^^^^^ unknown field
     |
     = note: available fields are: `players`, `turn_order`, `battlefield`, `stack`, `exile` ... and 17 others

error[E0609]: no field `cards` on type `state::GameState`
    --> mtg-engine/src/game.rs:2381:20
     |
2381 |         game.state.cards.insert(c3_id, card3);
     |                    ^^^^^ unknown field
     |
     = note: available fields are: `players`, `turn_order`, `battlefield`, `stack`, `exile` ... and 17 others

For more information about this error, try `rustc --explain E0609`.
error: could not compile `mtg-engine` (lib test) due to 3 previous errors

Need to check how cards are added to a player's hand in the existing tests. Let me look at how hand works:

668-            if !player.mana_pool.try_pay(&mana_cost) {
669-                // Can't pay — put card back in hand
670:                player.hand.add(card_id);
671-                return;
672-            }
--
995-                            let owner = perm.owner();
996-                            if let Some(player) = self.state.players.get_mut(&owner) {
997:                                player.hand.add(target_id);
998-                            }
999-                            self.state.set_zone(target_id, crate::constants::Zone::Hand, Some(owner));
--
1195-                            if let Some(player) = self.state.players.get_mut(&owner_id) {
1196-                                if player.graveyard.remove(target_id) {
1197:                                    player.hand.add(target_id);
1198-                                    self.state.set_zone(target_id, crate::constants::Zone::Hand, Some(owner_id));
1199-                                }
--
1343-                            if let Some(player) = self.state.players.get_mut(&controller) {
1344-                                player.library.remove(card_id);
1345:                                player.hand.add(card_id);
1346-                                self.state.set_zone(card_id, crate::constants::Zone::Hand, Some(controller));
1347-                            }
--
1448-            // Add to hand and update zone
1449-            if let Some(player) = self.state.players.get_mut(&player_id) {
1450:                player.hand.add(card_id);
1451-            }
1452-            self.state.set_zone(card_id, crate::constants::Zone::Hand, Some(player_id));
--
2381-        game.state.cards.insert(c3_id, card3);
2382-        if let Some(player) = game.state.players.get_mut(&p2) {
2383:            player.hand.add(c1_id);
2384:            player.hand.add(c2_id);
2385:            player.hand.add(c3_id);
2386-        }
2387-

The hand just needs add — I don't need to insert into a cards map. The move_card_to_graveyard_inner only needs the card to exist in the hand (via hand.remove). Let me simplify the test:

>cd /mnt/dest-btrfs/home/jc/src/mage/mtg-rl && cargo test --lib -p mtg-engine -- discard_opponents_effect 2>&1

Exit code 101
   Compiling mtg-engine v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-engine)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 5.18s
     Running unittests src/lib.rs (target/debug/deps/mtg_engine-fa37b04e04026fe5)

running 1 test
test game::tests::discard_opponents_effect ... FAILED

failures:

---- game::tests::discard_opponents_effect stdout ----

thread 'game::tests::discard_opponents_effect' panicked at mtg-engine/src/game.rs:2392:9:
assertion `left == right` failed
  left: 3
 right: 2
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    game::tests::discard_opponents_effect

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 159 filtered out; finished in 0.00s

error: test failed, to rerun pass `-p mtg-engine --lib`

The discard isn't working. Let me check move_card_to_graveyard_inner:

OK so move_card_to_graveyard_inner doesn't do hand.remove. Looking back at the DiscardCards handler, it does player.hand.remove(card_id) separately, then calls move_card_to_graveyard_inner. The issue is that in my DiscardOpponents handler, choose_discard returns an empty vec because AlwaysPassPlayer::choose_discard returns vec![]. Let me check:

Yes, AlwaysPassPlayer::choose_discard returns vec![], and so the decision maker returns empty — no cards get discarded. The fallback hand.iter().rev().take(...) only fires when self.decision_makers.get_mut(&opp) returns None, but it won't because we registered decision makers for both players.

I need to adjust the test to not register a decision maker for p2, or use a different approach. Let me look at how the existing DiscardCards test works... actually there's no separate DiscardCards test in game.rs. Let me fix the test by directly testing without decision makers (the fallback path), or better, let me check the hand count after the fact properly. The issue is the decision maker returns empty vec.

Let me fix the test to verify the fallback path by creating the game differently, or I can just directly verify the mechanism works by checking that the effect processes without a decision maker:

>cd /mnt/dest-btrfs/home/jc/src/mage/mtg-rl && cargo test --lib -p mtg-engine -- discard_opponents_effect 2>&1

   Compiling mtg-engine v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-engine)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 2.75s
     Running unittests src/lib.rs (target/debug/deps/mtg_engine-fa37b04e04026fe5)

running 1 test
test game::tests::discard_opponents_effect ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 159 filtered out; finished in 0.00s

Engine work done. Now let me fix the cards. Let me handle each one:

Burglar Rat (FDN line 617) — simple swap to Effect::discard_opponents(1)

Dream Seizer (ECL line 596) — compound: add_counters("-1/-1", 1) + discard_opponents(1) (self-counter uses Batch 2 source fallback)

Arbiter of Woe (FDN line 5340) — compound: discard_opponents(1) + lose_life_opponents(2) + draw_cards(1) + gain_life(2)

Bloodtithe Collector (FDN line 5520) — conditional ("if an opponent lost life this turn"), keep as Custom with note, or implement partially

Let me fix the straightforward ones first:

Good. Now fix Dream Seizer (ECL):

Good. Now fix Arbiter of Woe (FDN line 5340):

Now for Bloodtithe Collector — it's conditional ("if an opponent lost life this turn"). We don't have conditional effect support, so I'll partially fix it by using the typed effect but note it's still conditional:

This one has a conditional — "if an opponent lost life this turn". The condition check isn't implemented, but I can still replace the Custom effect with the typed effect. The trigger will fire unconditionally (which is a simplification, but better than being a no-op Custom):

Now let me verify compilation and run all tests:

>cargo test --lib 2>&1

   Compiling mtg-engine v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-engine)
   Compiling mtg-cards v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-cards)
   Compiling mtg-ai v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-ai)
warning: fields `action` and `depth` are never read
  --> mtg-ai/src/minimax_player.rs:62:5
   |
60 | struct SearchNode {
   |        ---------- fields in this struct
61 |     /// The action that led to this node (None for root).
62 |     action: Option<PlayerAction>,
   |     ^^^^^^
...
70 |     depth: u32,
   |     ^^^^^
   |
   = note: `SearchNode` has derived impls for the traits `Debug` and `Clone`, but these are intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default

warning: associated functions `new_root` and `new_child` are never used
  --> mtg-ai/src/minimax_player.rs:74:8
   |
73 | impl SearchNode {
   | --------------- associated functions in this implementation
74 |     fn new_root(is_maximizing: bool) -> Self {
   |        ^^^^^^^^
...
84 |     fn new_child(action: PlayerAction, depth: u32, is_maximizing: bool) -> Self {
   |        ^^^^^^^^^

warning: `mtg-ai` (lib) generated 2 warnings
   Compiling mtg-tests v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-tests)
   Compiling mtg-python v0.1.0 (/mnt/dest-btrfs/home/jc/src/mage/mtg-rl/mtg-python)
warning: `mtg-ai` (lib test) generated 1 warning (1 duplicate)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 9.46s
     Running unittests src/lib.rs (target/debug/deps/mtg_ai-a3cefc6981511e97)

running 52 tests
test action_space::tests::action_mask_with_castable_spell ... ok
test action_space::tests::phase1_activate_ability_roundtrip ... ok
test action_space::tests::action_mask_pass_only ... ok
test action_space::tests::phase1_all_indices_are_unique ... ok
test action_space::tests::phase1_cast_spell_roundtrip ... ok
test action_space::tests::phase1_out_of_range_returns_none ... ok
test action_space::tests::phase1_pass_roundtrip ... ok
test action_space::tests::phase1_play_land_roundtrip ... ok
test action_space::tests::phase2_roundtrip ... ok
test action_space::tests::reward_intermediate_negative_when_losing_advantage ... ok
test action_space::tests::reward_intermediate_positive_when_gaining_advantage ... ok
test action_space::tests::reward_loss_is_negative ... ok
test action_space::tests::reward_win_is_positive ... ok
test evaluator::tests::creature_permanent_scores_positively ... ok
test evaluator::tests::equal_board_state_scores_zero ... ok
test evaluator::tests::flying_creature_scores_higher ... ok
test evaluator::tests::keyword_scores_are_reasonable ... ok
test evaluator::tests::life_score_above_20 ... ok
test evaluator::tests::life_score_lookup_table ... ok
test evaluator::tests::loss_state_gives_min_score ... ok
test evaluator::tests::more_life_is_better ... ok
test evaluator::tests::win_state_gives_max_score ... ok
test gym::tests::env_action_mask_has_correct_size ... ok
test gym::tests::env_space_sizes ... ok
test gym::tests::env_reset_returns_correct_size_observation ... ok
test gym::tests::env_step_returns_valid_result ... ok
test heuristic_player::tests::heuristic_attacks_with_all ... ok
test gym::tests::env_truncates_at_max_turns ... ok
test heuristic_player::tests::heuristic_choose_use_says_yes_except_ai_dont_use ... ok
test heuristic_player::tests::heuristic_damage_assignment_correct_total ... ok
test heuristic_player::tests::heuristic_mulligan_keeps_small_hands ... ok
test heuristic_player::tests::heuristic_mulligan_mulligans_7_card_hand ... ok
test heuristic_player::tests::heuristic_passes_when_only_option ... ok
test heuristic_player::tests::heuristic_pile_prefers_larger_for_good ... ok
test heuristic_player::tests::heuristic_prefers_land_over_pass ... ok
test heuristic_player::tests::heuristic_prefers_land_over_spell ... ok
test heuristic_player::tests::heuristic_prefers_spell_over_pass ... ok
test minimax_player::tests::minimax_ab_alpha_beta_pruning ... ok
test minimax_player::tests::minimax_free_spell_preferred_over_regular ... ok
test minimax_player::tests::minimax_passes_when_only_option ... ok
test minimax_player::tests::minimax_prefers_land_over_spell ... ok
test minimax_player::tests::minimax_prefers_spell_over_pass ... ok
test minimax_player::tests::minimax_search_stats_tracked ... ok
test observation::tests::life_normalized_correctly ... ok
test observation::tests::observation_has_correct_size ... ok
test observation::tests::observation_size_constant_matches ... ok
test observation::tests::permanents_are_padded ... ok
test observation::tests::phase_one_hot_encoding ... ok
test random_player::tests::random_player_chooses_from_legal_actions ... ok
test random_player::tests::random_player_choose_use_returns_bool ... ok
test random_player::tests::random_player_passes_when_only_option ... ok
test random_player::tests::random_player_damage_assignment_sums_correctly ... ok

test result: ok. 52 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

     Running unittests src/lib.rs (target/debug/deps/mtg_cards-c237fd9c64d2d797)

running 18 tests
test keywords::behold::tests::behold_elf_cost ... ok
test keywords::behold::tests::behold_goblin_cost ... ok
test keywords::behold::tests::behold_rules_text_format ... ok
test keywords::blight::tests::blight_1_cost ... ok
test keywords::blight::tests::blight_2_cost ... ok
test keywords::blight::tests::blight_rules_text_plural ... ok
test keywords::blight::tests::blight_rules_text_singular ... ok
test keywords::mobilize::tests::mobilize_1_creates_triggered_ability ... ok
test keywords::mobilize::tests::mobilize_2_creates_two_tokens ... ok
test keywords::mobilize::tests::mobilize_3 ... ok
test registry::tests::ecl_specific_cards ... ok
test registry::tests::fdn_tier2_cards ... ok
test registry::tests::ecl_tier2_spells ... ok
test registry::tests::fdn_tier3_cards ... ok
test registry::tests::registry_card_counts ... ok
test registry::tests::registry_create_and_lookup ... ok
test registry::tests::registry_set_query ... ok
test registry::tests::tdm_tier2_spells ... ok

test result: ok. 18 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

     Running unittests src/lib.rs (target/debug/deps/mtg_engine-10c8e693567e8570)

running 160 tests
test abilities::tests::activated_ability ... ok
test abilities::tests::ability_store ... ok
test abilities::tests::active_zones ... ok
test abilities::tests::attacks_triggered ... ok
test abilities::tests::combat_damage_triggered ... ok
test abilities::tests::compose_realistic_card_lightning_bolt ... ok
test abilities::tests::compose_realistic_card_llanowar_elves ... ok
test abilities::tests::compose_realistic_card_mulldrifter ... ok
test abilities::tests::compose_realistic_lord ... ok
test abilities::tests::cost_builders ... ok
test abilities::tests::dies_triggered ... ok
test abilities::tests::effect_builders ... ok
test abilities::tests::end_step_triggered ... ok
test abilities::tests::etb_triggered ... ok
test abilities::tests::mana_ability ... ok
test abilities::tests::optional_trigger ... ok
test abilities::tests::spell_ability ... ok
test abilities::tests::static_ability_boost ... ok
test abilities::tests::static_effect_builders ... ok
test abilities::tests::triggered_ability ... ok
test abilities::tests::upkeep_triggered ... ok
test card::tests::create_basic_creature ... ok
test card::tests::create_basic_land ... ok
test combat::tests::blocked_damage ... ok
test combat::tests::blocker_damage_timing ... ok
test combat::tests::blocking ... ok
test combat::tests::combat_clear ... ok
test combat::tests::combat_state_basics ... ok
test combat::tests::deathtouch_minimizes_damage ... ok
test combat::tests::double_strike_both_steps ... ok
test combat::tests::first_strike_timing ... ok
test combat::tests::flying_blocks ... ok
test combat::tests::menace_requires_two_blockers ... ok
test combat::tests::trample_overflow ... ok
test combat::tests::unblocked_damage ... ok
test counters::tests::add_and_remove_counters ... ok
test counters::tests::counter_type_from_name ... ok
test counters::tests::pt_modification ... ok
test effects::tests::boost_effect ... ok
test effects::tests::keyword_grant_effect ... ok
test effects::tests::continuous_effects_manager ... ok
test effects::tests::remove_from_source ... ok
test effects::tests::replacement_effects ... ok
test effects::tests::timestamp_ordering ... ok
test events::tests::applied_effects_tracking ... ok
test events::tests::combat_events ... ok
test events::tests::damage_player_convenience ... ok
test events::tests::event_builder ... ok
test events::tests::event_log ... ok
test events::tests::prevention ... ok
test events::tests::spell_cast_event ... ok
test filters::tests::filter_card_data ... ok
test events::tests::zone_change_event ... ok
test filters::tests::filter_color ... ok
test filters::tests::filter_controller ... ok
test filters::tests::filter_creature ... ok
test filters::tests::filter_keyword ... ok
test filters::tests::filter_mana_value ... ok
test filters::tests::filter_nonland_permanent ... ok
test filters::tests::filter_not_combinator ... ok
test filters::tests::filter_or_combinator ... ok
test filters::tests::filter_power_comparison ... ok
test filters::tests::filter_tapped_untapped ... ok
test game::tests::activated_ability_goes_on_stack ... ok
test game::tests::add_counters_self_when_no_targets ... ok
test game::tests::bounce_effect ... ok
test game::tests::counter_annihilation_applied ... ok
test game::tests::discard_opponents_effect ... ok
test game::tests::draw_cards_from_empty_library_causes_loss ... ok
test game::tests::exile_effect ... ok
test game::tests::draw_cards_effect ... ok
test game::tests::fizzle_when_target_removed ... ok
test game::tests::gain_life_effect ... ok
test game::tests::game_creation ... ok
test game::tests::lose_life_opponents_effect ... ok
test game::tests::legal_actions_include_pass ... ok
test game::tests::legend_rule_applied ... ok
test game::tests::mana_ability_and_spell_cast ... ok
test mana::tests::can_pay_generic ... ok
test mana::tests::can_pay_colored ... ok
test game::tests::pay_costs_tap_and_sacrifice ... ok
test mana::tests::cost_colors ... ok
test mana::tests::mana_display ... ok
test game::tests::spell_effects_execute_on_resolve ... ok
test mana::tests::parse_simple_cost ... ok
test mana_pool::tests::add_and_spend_colored ... ok
test mana_pool::tests::any_mana_pays_colored ... ok
test mana::tests::mana_arithmetic ... ok
test mana_pool::tests::clear_empties_pool ... ok
test mana_pool::tests::color_array ... ok
test mana::tests::cannot_pay_insufficient ... ok
test mana_pool::tests::spend_generic_prefers_colorless ... ok
test permanent::tests::creature_basics ... ok
test permanent::tests::damage_and_lethal ... ok
test mana_pool::tests::try_pay_atomic ... ok
test permanent::tests::haste_ignores_summoning_sickness ... ok
test permanent::tests::tap_untap ... ok
test permanent::tests::counters_modify_pt ... ok
test player::tests::discard_check ... ok
test permanent::tests::keyword_grants ... ok
test player::tests::find_card_in_zones ... ok
test permanent::tests::defender_cannot_attack ... ok
test player::tests::game_over_states ... ok
test player::tests::land_plays ... ok
test player::tests::life_changes ... ok
test player::tests::poison_counters ... ok
test player::tests::starting_values ... ok
test state::tests::can_cast_sorcery ... ok
test state::tests::initial_state ... ok
test state::tests::next_player_wraps ... ok
test state::tests::sba_counter_annihilation ... ok
test state::tests::sba_indestructible_survives_damage ... ok
test state::tests::sba_legend_rule ... ok
test state::tests::sba_legend_rule_different_controllers ... ok
test state::tests::sba_lethal_damage ... ok
test state::tests::sba_life_loss ... ok
test state::tests::sba_no_counter_annihilation_when_only_one_type ... ok
test state::tests::sba_planeswalker_zero_loyalty ... ok
test state::tests::sba_poison ... ok
test state::tests::should_end_one_player_left ... ok
test state::tests::sba_zero_toughness ... ok
test state::tests::zone_tracking ... ok
test targets::tests::divided_amounts ... ok
test targets::tests::empty_targets ... ok
test targets::tests::mark_illegal ... ok
test targets::tests::mark_player_illegal ... ok
test targets::tests::selected_targets_objects ... ok
test targets::tests::selected_targets_players ... ok
test targets::tests::target_definition_basics ... ok
test targets::tests::target_definition_up_to ... ok
test turn::tests::end_turn_skips_to_cleanup ... ok
test turn::tests::extra_turns ... ok
test turn::tests::extra_turns_lifo ... ok
test turn::tests::first_strike_step ... ok
test turn::tests::priority_rules ... ok
test turn::tests::priority_tracking ... ok
test turn::tests::step_to_phase_mapping ... ok
test turn::tests::turn_rotation ... ok
test turn::tests::turn_step_sequence ... ok
test watchers::tests::custom_watcher_card_scope ... ok
test watchers::tests::custom_watcher_game_scope ... ok
test watchers::tests::custom_watcher_player_scope ... ok
test watchers::tests::custom_watcher_reset ... ok
test watchers::tests::reset_clears_stats ... ok
test watchers::tests::track_attackers ... ok
test watchers::tests::track_cards_drawn ... ok
test watchers::tests::track_creatures_died ... ok
test watchers::tests::track_enters_battlefield ... ok
test watchers::tests::track_life_gained ... ok
test watchers::tests::track_spells_cast ... ok
test zones::tests::battlefield_add_remove ... ok
test zones::tests::battlefield_controlled_by ... ok
test zones::tests::exile_zones ... ok
test zones::tests::hand_add_remove ... ok
test zones::tests::graveyard_ordering ... ok
test zones::tests::library_draw ... ok
test zones::tests::library_peek ... ok
test zones::tests::library_put_on_top_and_bottom ... ok
test zones::tests::stack_lifo ... ok
test game::tests::game_runs_to_completion ... ok

test result: ok. 160 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.04s

     Running unittests src/lib.rs (target/debug/deps/mtg_python-d2f2ac684d6d76ac)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running unittests src/lib.rs (target/debug/deps/mtg_tests-fac26c7f0fd5aee5)

running 17 tests
test concurrency::tests::game_state_clone_is_independent ... ok
test framework::tests::framework_bolt_kills_bear ... ok
test framework::tests::framework_draw_cards_effect ... ok
test framework::tests::framework_custom_starting_life ... ok
test framework::tests::framework_direct_effect_execution ... ok
test concurrency::tests::gymnasium_env_runs_end_to_end ... ok
test framework::tests::framework_gain_life_effect ... ok
test framework::tests::framework_exile_and_assert ... ok
test framework::tests::framework_life_totals ... ok
test framework::tests::framework_multiple_permanents ... ok
test framework::tests::framework_setup_graveyard ... ok
test framework::tests::framework_setup_battlefield ... ok
test framework::tests::framework_setup_hand ... ok
test concurrency::tests::throughput_baseline ... ok
test concurrency::tests::parallel_games_complete_without_panic ... ok
test concurrency::tests::parallel_games_produce_varied_results ... ok
test concurrency::tests::parallel_gymnasium_envs ... ok

test result: ok. 17 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.64s

All 247 tests pass. Now let me also scan for any other cards across all sets that might use "opponent discards" patterns I missed:

mtg-cards/src/sets/fdn.rs:616:                "When Burglar Rat enters, each opponent discards a card.",
mtg-cards/src/sets/fdn.rs:617:                vec![Effect::discard_opponents(1)],
mtg-cards/src/sets/fdn.rs:1851:    // 5/5 Dragon Wizard for {5}{R}{R}. Flying. Combat damage: all discard + draw 7.
mtg-cards/src/sets/fdn.rs:1858:                "Whenever Dragon Mage deals combat damage to a player, each player discards their hand, then draws seven cards.",
mtg-cards/src/sets/fdn.rs:1860:                vec![Effect::Custom("Each player discards their hand, then draws seven cards.".into())],
mtg-cards/src/sets/fdn.rs:2363:    // Sorcery {B}. Target opponent reveals hand; you choose a noncreature, nonland card to discard.
mtg-cards/src/sets/fdn.rs:2368:                vec![Effect::discard_cards(1)],
mtg-cards/src/sets/fdn.rs:2436:    // Sorcery {1}{U}. Draw 2. Discard 1 unless you attacked this turn.
mtg-cards/src/sets/fdn.rs:2441:                vec![Effect::draw_cards(2), Effect::discard_cards(1)],
mtg-cards/src/sets/fdn.rs:2448:    // Sorcery {1}{B}. Return up to 2 creature cards from graveyard to hand, discard 1.
mtg-cards/src/sets/fdn.rs:2453:                vec![Effect::return_from_graveyard(), Effect::discard_cards(1)],
mtg-cards/src/sets/fdn.rs:5338:                "When this creature enters, each opponent discards a card and loses 2 life. You draw a card and gain 2 life.",
mtg-cards/src/sets/fdn.rs:5340:                vec![Effect::discard_opponents(1), Effect::lose_life_opponents(2), Effect::draw_cards(1), Effect::gain_life(2)],
mtg-cards/src/sets/fdn.rs:5518:                "When this creature enters, if an opponent lost life this turn, each opponent discards a card.",
mtg-cards/src/sets/fdn.rs:5520:                vec![Effect::discard_opponents(1)],
mtg-cards/src/sets/fdn.rs:6340:                "When this creature enters, draw a card, then discard a card.",
mtg-cards/src/sets/fdn.rs:6342:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/fdn.rs:6431:                "When Kiora enters, draw two cards, then discard two cards.",
mtg-cards/src/sets/fdn.rs:6433:                vec![Effect::Custom("When Kiora enters, draw two cards, then discard two cards.".into())],
mtg-cards/src/sets/fdn.rs:6740:                vec![Effect::Custom("Whenever an opponent casts a spell, that player loses 5 life unless they discard a card.".into())],
mtg-cards/src/sets/fdn.rs:6752:                vec![Effect::Custom("Target opponent reveals their hand. You choose a nonland card from it. That player discards that card.".into())],
mtg-cards/src/sets/fdn.rs:6896:                vec![Effect::counter_spell(), Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/fdn.rs:7084:                vec![Effect::Custom("As an additional cost to cast this spell, discard a card.".into())],
mtg-cards/src/sets/fdn.rs:7302:                vec![Effect::Custom("As an additional cost to cast this spell, discard a card.".into())],
mtg-cards/src/sets/tla.rs:580:                    vec![Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:588:    // 3/2 Faerie Rogue for {3}{B}. Flying. (ETB: blight 1 => opponents discard)
mtg-cards/src/sets/ecl.rs:595:                "When Dream Seizer enters, put a -1/-1 counter on it. When you do, each opponent discards a card.",
mtg-cards/src/sets/ecl.rs:596:                vec![Effect::add_counters("-1/-1", 1), Effect::discard_opponents(1)],
mtg-cards/src/sets/ecl.rs:806:                "When Flaring Cinder enters, you may draw a card, then discard a card.",
mtg-cards/src/sets/ecl.rs:807:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:810:                "Whenever you cast a spell with mana value 4 or greater, you may draw a card, then discard a card.",
mtg-cards/src/sets/ecl.rs:812:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:957:                "{T}, Blight 1: Draw a card, then discard a card.",
mtg-cards/src/sets/ecl.rs:959:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:999:    // 3/1 Elf Warrior for {1}{B}. (Discard: indestructible + tap)
mtg-cards/src/sets/ecl.rs:1005:                "Discard a card: Iron-Shield Elf gains indestructible until end of turn. Tap it.",
mtg-cards/src/sets/ecl.rs:1006:                vec![Cost::Discard(1)],
mtg-cards/src/sets/ecl.rs:1055:                vec![Cost::pay_mana("{2}"), Cost::Discard(1)],
mtg-cards/src/sets/ecl.rs:1400:    // 2/3 Merfolk Citizen for {2}{U}. (Becomes tapped: draw, discard)
mtg-cards/src/sets/ecl.rs:1407:                "Whenever Silvergill Peddler becomes tapped, draw a card, then discard a card.",
mtg-cards/src/sets/ecl.rs:1409:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:1785:    // Instant {3}{U}{U}. Convoke. Draw 3, discard 1.
mtg-cards/src/sets/ecl.rs:1789:        abilities: vec![Ability::spell(id, vec![Effect::draw_cards(3), Effect::discard_cards(1)], TargetSpec::None)],
mtg-cards/src/sets/ecl.rs:2031:    // Sorcery for {1}{B}. Choose one: opponent discards nonland permanent card; or target creature gets -2/-2 until EOT.
mtg-cards/src/sets/ecl.rs:2035:            vec![Effect::Custom("Choose one: target opponent reveals hand, discard a nonland permanent card; or target creature gets -2/-2 until end of turn.".into())],
mtg-cards/src/sets/ecl.rs:2412:    // ETB if {B}{B}: opponent reveals hand, discard nonland card.
mtg-cards/src/sets/ecl.rs:2424:                "When this creature enters, if {B}{B} was spent to cast it, target opponent reveals their hand. You choose a nonland card from it. That player discards that card.",
mtg-cards/src/sets/ecl.rs:2425:                vec![Effect::discard_cards(1)],
mtg-cards/src/sets/ecl.rs:3789:                "When this creature enters, you may discard a card. If you do, search your library for a creature card, reveal it, put it into your hand, then shuffle.",
mtg-cards/src/sets/ecl.rs:3791:                vec![Effect::Custom("When this creature enters, you may discard a card. If you do, search your library for a creature card, reveal it, put it into your hand, then shuffle.".into())],
mtg-cards/src/sets/ecl.rs:4168:                vec![Effect::Custom("Draw three cards. Then discard two cards unless you discard a creature card.".into())],
mtg-cards/src/sets/tdm.rs:908:                "Whenever this creature becomes tapped, you may discard a card. If you do, draw a card.",
mtg-cards/src/sets/tdm.rs:910:                vec![Effect::Custom("You may discard a card. If you do, draw a card.".into())],
mtg-cards/src/sets/tdm.rs:1066:                "When this creature enters, draw a card, then discard a card.",
mtg-cards/src/sets/tdm.rs:1067:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/tdm.rs:1897:    // Enchantment {1}{U}. ETB: draw 2, discard 1. Dragon ETB: return to hand.
mtg-cards/src/sets/tdm.rs:1902:                "When this enchantment enters, draw two cards, then discard a card.",
mtg-cards/src/sets/tdm.rs:1903:                vec![Effect::draw_cards(2), Effect::discard_cards(1)],
mtg-cards/src/sets/tdm.rs:2344:    // Jeskai: whenever you cast noncreature spell, draw a card then discard.
mtg-cards/src/sets/tdm.rs:2354:                "Jeskai — Whenever you cast a noncreature spell, draw a card, then discard a card.",
mtg-cards/src/sets/tdm.rs:2355:                vec![Effect::draw_cards(1), Effect::discard_cards(1)],
mtg-cards/src/sets/tdm.rs:2599:    // Instant {4}{U}. Costs {2} less if you cast another spell this turn. Draw 3, discard 1.
mtg-cards/src/sets/tdm.rs:2607:                vec![Effect::draw_cards(3), Effect::discard_cards(1)],
mtg-cards/src/sets/tdm.rs:3107:                "At the beginning of your end step, you may discard your hand. If you do, draw cards equal to the number of spells you've cast this turn.",
mtg-cards/src/sets/tdm.rs:3109:                vec![Effect::Custom("You may discard your hand. If you do, draw cards equal to the number of spells you've cast this turn.".into())],
mtg-cards/src/sets/tdm.rs:3328:                    "When this creature enters, it deals 2 damage to any target and you gain 2 life. If a player is dealt damage this way, they discard a card.",
mtg-cards/src/sets/tdm.rs:3330:                         Effect::Custom("If a player is dealt damage this way, they discard a card.".into())],
mtg-cards/src/sets/tdm.rs:3493:                    "Whenever this creature attacks, you may draw a card. If you do, discard a card.",
mtg-cards/src/sets/tdm.rs:3494:                    vec![Effect::DrawCards { count: 1 }, Effect::DiscardCards { count: 1 }],
mtg-cards/src/sets/tdm.rs:3511:                    "When Tersa Lightshatter enters, discard up to two cards, then draw that many cards.",
mtg-cards/src/sets/tdm.rs:3512:                    vec![Effect::Custom("Discard up to two cards, then draw that many cards.".into())],
mtg-cards/src/sets/tdm.rs:3818:                vec![Effect::DrawCards { count: 1 }, Effect::Custom("You may discard a card. When you discard a nonland card this way, Glacial Dragonhunt deals 3 damage to target creature.".into())],
mtg-cards/src/sets/tdm.rs:3981:                "{1}{R}, Discard your hand, Sacrifice this enchantment: Draw two cards.",
mtg-cards/src/sets/tdm.rs:3982:                vec![Cost::pay_mana("{1}{R}"), Cost::Custom("Discard your hand".into()), Cost::SacrificeSelf],
mtg-cards/src/sets/tdm.rs:4077:                "Ward -- Discard a card.",
mtg-cards/src/sets/tdm.rs:4078:                vec![StaticEffect::Custom("Ward -- Discard a card.".into())]),
mtg-cards/src/sets/tdm.rs:4267:                vec![Effect::DrawCards { count: 3 }, Effect::Custom("Discard two cards unless you discard a creature card.".into())],

I see one more potential match: FDN line 6433 — Kiora, "draw two cards, then discard two cards" — that's already just controller loot, not opponent discard. The rest are either controller self-discard or complex conditional effects. No additional opponent discards patterns missed.

Now let me update the docs. First, the work queue:

Now update the per-set remediation docs. Let me read them to find the right sections:

451:*(Many more partial cards exist in the Tier 3 batch 2+ sections -- see Stub section for cards that degrade further)*
548:*(This section continues for approximately 230 more cards. The pattern is the same: cards from the Tier 3 batch 2 onward (line ~3170 in fdn.rs) through the "New Creatures", "New Instants and Sorceries", "New Lands", "New Artifacts", "New Enchantments", and "Other" sections all use generic placeholder `Effect::Custom("ETB effect.")`, `Effect::Custom("Spell effect.")`, `StaticEffect::Custom("Static effect.")` etc. These are all stubs.)*

3:## Overview
13:## How to Fix Cards
15:### Engine Context
85:### Adding a New Effect Type
100:## Complete Cards
216:## Partial Cards
455:## Stub Cards
459:### Cards with generic placeholder Custom effects (all non-functional)
550:### Notable high-value stubs that should be prioritized:
566:## Missing Cards
572:## Priority Remediation Roadmap
574:### Phase 1: Engine effects (unblocks many cards at once)
584:### Phase 2: Fix easy card-level issues
592:### Phase 3: Equipment system
596:### Phase 4: Modal spells and complex effects
602:### Phase 5: Complete remaining stubs

Now update ECL remediation:

Now update ROADMAP.md:

11:[Omitted long matching line]
118:   - ~~Pulse Tracker/Marauding Blight-Priest/Vampire Spawn/Vampire Neonate: `Custom("Each opponent loses N life")` -> `LoseLifeOpponents { amount: N }`~~ **DONE**
119:   - ~~Skirmish Rhino (TDM), Champion of the Weird (ECL), Boggart Mischief (ECL): opponent life loss Custom -> `LoseLifeOpponents`~~ **DONE**
159:16. **Learn** (TLA) -- May discard to draw keyword action.

Now update the memory to record the new API:

Let me do a final verification that everything compiles and all tests pass:

>cargo check -p mtg-cards && cargo test --lib 2>&1 | tail -20

test concurrency::tests::game_state_clone_is_independent ... ok
test framework::tests::framework_bolt_kills_bear ... ok
test framework::tests::framework_custom_starting_life ... ok
test framework::tests::framework_draw_cards_effect ... ok
test framework::tests::framework_direct_effect_execution ... ok
test framework::tests::framework_exile_and_assert ... ok
test framework::tests::framework_gain_life_effect ... ok
test concurrency::tests::gymnasium_env_runs_end_to_end ... ok
test framework::tests::framework_life_totals ... ok
test framework::tests::framework_multiple_permanents ... ok
test framework::tests::framework_setup_battlefield ... ok
test framework::tests::framework_setup_graveyard ... ok
test framework::tests::framework_setup_hand ... ok
test concurrency::tests::parallel_gymnasium_envs ... ok
test concurrency::tests::parallel_games_produce_varied_results ... ok
test concurrency::tests::parallel_games_complete_without_panic ... ok
test concurrency::tests::throughput_baseline ... ok

test result: ok. 17 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.61s
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s

All 247 tests pass (52 + 18 + 160 + 17). Batch 3 is complete.

Summary: Batch 3 — OpponentDiscards

Engine changes:

Added Effect::DiscardOpponents { count: u32 } variant to the Effect enum
Added Effect::discard_opponents(count) constructor
Added match arm in execute_effects — iterates opponents, each calls choose_discard on their decision maker, then moves discarded cards to graveyard
Added test discard_opponents_effect (with a DiscardingPlayer decision maker that actually selects cards to discard)

Cards fixed (4):

Card	Set	Change
Burglar Rat	FDN	`Custom("Each opponent discards...")` → `discard_opponents(1)`
Arbiter of Woe	FDN	Compound Custom → `discard_opponents(1), lose_life_opponents(2), draw_cards(1), gain_life(2)`
Bloodtithe Collector	FDN	Conditional Custom → `discard_opponents(1)` (condition not modeled)
Dream Seizer	ECL	Compound Custom → `add_counters("-1/-1", 1), discard_opponents(1)`

Docs updated: work-queue.md, fdn-remediation.md, ecl-remediation.md, ROADMAP.md, MEMORY.md