fix(engine): Bring to Light free-cast is resolution-only, not a lingering permission (#2880)

[matthewevans]

Summary

Closes #2880.

Bring to Light's "You may cast that card without paying its mana cost" granted an indefinite ExileWithAltCost permission, so the free cast could be taken at any later priority for the rest of the game. Per CR 608.2g the cast happens during the spell's resolution; the permission must not linger.

This is a class fix for the resolution-only free-cast family (~28 Cast-mode cards), root-caused in two layers:

• Parser (oracle_effect/mod.rs, Branch-1 ParentTarget anaphor arm only): emit CastFromZoneDriver::DuringResolution for a bare free cast (mode == Cast && without_paying && alt_ability_cost.is_none() && duration.is_none() && constraint.is_none()), else LingeringPermission.
• Engine (cast_from_zone.rs): generalized the self_free_cast guard (renamed driver_free_cast) by dropping the Suspend-specific target == source clause, so a tutored card (target ≠ source, in the controller's own exile) routes through cast_single_target_during_resolution like Suspend/Memory Plunder.

Deliberately excluded (stay on the lingering-permission path)

• Play-mode hideaway/wish lands (Mosswort Bridge, Windbrisk Heights, Shelldock Isle, Djinn of Wishes…) — mode == Play; land play is a special action (CR 305.1), not a during-resolution cast.
• Alternative-cost recasts (The Infamous Cruelclaw's discard) — alt_ability_cost.
• Durational recasts — explicit duration.
• Constrained free-casts with a not-cast fallback (Beseech the Mirror: "cast the exiled card … if that spell's mana value is 4 or less … put it into your hand if it wasn't cast this way") — constraint; the constraint is evaluated when the permission is exercised and the fallback depends on the standing permission.
• Cascade/Etali/Jeleva from among them / ExiledBySource arms — untouched.
• the copy (Isochron Scepter, Elite Arcanist) — folds to CastCopyOfCard before reaching the resolver; driver irrelevant.

Tests

New bring_to_light_free_cast_2880.rs drives the real parser+resolver pipeline: accept → tutored card reaches the stack and leaves no standing permission; decline → stays in exile with no lingering permission. Both fail on revert.

Verification

Local Tilt clippy + test-engine green (including the Beseech constraint-path regression guard beseech_bargained_accept_grants_cast_without_hand_fallback). Independent /review-impl: APPROVED.

CR: 608.2g, 608.2c, 118.9/118.9b, 305.1, 701.23 (all grep-verified).

[gemini-code-assist]

Code Review

This pull request resolves issue #2880 by refactoring the DuringResolution cast-from-zone mechanism to support tutor-and-cast effects like Bring to Light, where the target card is not the source of the ability. The Suspend-specific target == source check has been removed, and a new integration test has been added to ensure no lingering casting permissions remain after resolution. The review feedback recommends adding defensive validation to return an error if a DuringResolution driver is specified but its structural invariants are not met, preventing a silent fallback to indefinite lingering permissions.

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[gemini-code-assist]

[MEDIUM] Prevent Silent Fallback to Indefinite Lingering Permissions

If a future card or effect uses the DuringResolution driver but fails any of the invariants (e.g., having multiple targets or an alternative cost), driver_free_cast will evaluate to false.

Currently, this causes the execution to silently fall through to grant_lingering_permissions. Because DuringResolution effects do not have a duration, this fall-through will stamp an indefinite ExileWithAltCost permission, allowing the player to cast the card at any later point in the game. This is a severe violation of CR 608.2g.

To enforce defensive programming and strict fidelity to the MTG Comprehensive Rules, we should explicitly return an error if the DuringResolution driver is specified but its structural invariants are not met.

Suggested change

	let driver_free_cast = driver.is_during_resolution()
	&& without_paying
	&& alt_ability_cost.is_none()
	&& target_ids.len() == 1
	&& target_ids[0] == ability.source_id;
	&& target_ids.len() == 1;
	let driver_free_cast = driver.is_during_resolution()
	&& without_paying
	&& alt_ability_cost.is_none()
	&& target_ids.len() == 1;
	if driver.is_during_resolution() && !driver_free_cast {
	return Err(EffectError::InvalidParam(
	"DuringResolution driver requires exactly one target and no alternative cost".to_string(),
	));
	}

References

1. Strict fidelity to the MTG Comprehensive Rules (CR) — every game rule, validation, and computed value matches the CR exactly. Ensure that invalid inputs or states are safely handled in all cases. ^(link)