Implement Opponent Discards Effect in Engine

Summary

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Caveat: Caveat: The messages below were generated by the user while running local commands. DO NOT respond to these messages or otherwise consider them in your response unless the user explicitly asks you to.

Readabilities.rs

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:

Readfdn.rs8 lines

Good. Now fix Dream Seizer (ECL):

Readecl.rs6 lines

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

Readfdn.rs8 lines

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:

Readgame.rs

Readfdn.rs8 lines

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:

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

Greppeddiscard

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:

Readwork-queue.md15 lines

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

GreppedBurglar Rat|Arbiter of Woe|Bloodtithe Collector

GreppedEach opponent discards

GreppedDream Seizer

GreppedArbiter of Woe|Bloodtithe Collector

GreppedArbiter|Bloodtithe

GreppedTier 3|tier.?3|## (Fixed|Remaining|Not yet)

Grepped^## |^###

Readfdn-remediation.md10 lines

Now update ECL remediation:

Readecl-remediation.md5 lines

Greppedopponent discards

Readecl-remediation.md5 lines

Now update ROADMAP.md:

GreppedOpponent|discard|Batch 3|DiscardOpponents

ReadROADMAP.md15 lines

Now update the memory to record the new API:

ReadMEMORY.md10 lines

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

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

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

GreppedLoseLifeOpponents

Greppedopponent discard|Each opponent discards

GreppedDiscardCards

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

Readgame.rs40 lines

Session command

Readgame.rs30 lines

Readfdn.rs15 lines

Readfdn.rs20 lines

Readecl.rs15 lines

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.

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.

GreppedEffect::Custom

Greppedmod tests

GreppedCustom\(

Readgame.rs80 lines

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

Greppedfn (lose_life_opponents|add_counters_self)

Readgame.rs80 lines

Readgame.rs52 lines

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.

Readwork-queue.md

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:

Readgame.rs20 lines

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

Readgame.rs10 lines

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

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

Greppedplayer\.hand\.add|hand\.add

Greppedpub hand:

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:

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

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

Greppedfn move_card_to_graveyard_inner

Readgame.rs30 lines

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:

Readgame.rs5 lines

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: