fix(parser): Gonti-class look-and-exile-face-down exiles the dug card, not the source (#1146)

[matthewevans]

Closes #1146.

Problem

Gonti, Lord of Luxury's ETB — "look at the top four cards of an opponent's library, exile one of them face down, then you may … play that card" — incorrectly exiled Gonti himself instead of the chosen card.

Root cause: the parser lowered "exile one of them face down" as a Dig { keep_count: 0 } peek + a sibling ChangeZone { target: ParentTarget → Exile }. At runtime the keep_count:0 peek short-circuits (dig.rs:96) without ever surfacing a DigChoice, so no card is selected; the sibling ChangeZone{ParentTarget} then resolves with an empty object-target set and falls back to source_id (targeting.rs:509) — exiling Gonti.

Fix

Fuse the clause into the Hideaway model: Dig { keep_count: Some(1), destination: Exile } + a HideawayConceal { ParentTarget } face-down step (mirrors database/hideaway.rs). The dug card is now player-selected and routed to exile by the Dig itself; the trailing "you may play that card" permission binds to it via the existing tracked-set publish.

Gated on an eof-anchored "exile one of them face down" recognizer so genuine pure-peek (Delver) and "exile target X card" siblings are untouched. Class fix (~17 cards: Thief of Sanity, Siphon Insight, …).

Test

gonti_lord_of_luxury_exiles_dug_card.rs drives the real cast pipeline:

• Discriminators: a DigChoice now surfaces (pre-fix it didn't); Gonti stays on the battlefield; the chosen library card is the exiled, face-down object.
• Regression guard: Delver-class pure-peek still lowers to keep_count:0 / no DigChoice.

Tilt test-engine green: gonti_exiles_the_dug_card_not_himself ... PASS, full suite 12772 passed.

CR

• CR 701.20e: looking is private. CR 406.3 / 708.2: face-down exile. CR 702.75a: Hideaway structural analog. CR 608.2c: continuation ordering.

Known follow-up (out of scope)

"an opponent's library" currently lowers to Controller (Gonti digs its own controller's library) — a separate parser gap, not this bug. Flagged for follow-up.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request implements support for the "exile one of them face down" continuation clause following a private Dig effect to resolve issue #1146, and adds regression tests for both Gonti's ETB behavior and the Station threshold teardown mechanic (issue #1134). The review feedback correctly identifies a compilation error in the 'append_conceal_sub_ability' helper due to a type mismatch when traversing the sub-ability chain, which must be resolved by calling '.as_mut()' on the boxed sub-ability.

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[gemini-code-assist]

The loop assignment will fail to compile because cursor is of type &mut AbilityDefinition, but .expect(...) returns &mut Box<AbilityDefinition>. To fix this type mismatch, you need to call .as_mut() on the boxed sub-ability to obtain a mutable reference to the inner AbilityDefinition, matching the pattern used elsewhere in this file.

Suggested change

	while cursor.sub_ability.is_some() {
	cursor = cursor
	.sub_ability
	.as_mut()
	.expect("sub_ability checked above");
	}
	while cursor.sub_ability.is_some() {
	cursor = cursor
	.sub_ability
	.as_mut()
	.expect("sub_ability checked above")
	.as_mut();
	}