feat(engine): model "As ~ is turned face up" as a TurnFaceUp replacement

[philluiz2323]

Problem

Cards whose turned-face-up triggered ability is templated with "As ~ is turned face up, [effect]" (rather than "When …") were unsupported — the clause fell through to an Unimplemented effect: Hooded Hydra (put five +1/+1 counters), Bubble Smuggler (put four +1/+1 counters), Gift of Doom (may attach it to a creature), Crowd-Control Warden.

The trigger classifier (has_trigger_prefix) only accepted when/whenever/at, so the "As"-led line routed to effect parsing. The engine already models TriggerMode::TurnFaceUp and fires it at runtime on GameEvent::TurnedFaceUp (trigger_matchers.rs), and the "When ~ is turned face up" form already parses — only the "As" templating (CR 711 megamorph/disguise + CR 603.3) was missing.

Fix

Recognize the "As" lead, scoped to the "is turned face up" phrase so "As ~ enters" replacements are untouched:

• has_trigger_prefix admits as … is turned face up, and
• the trigger core rewrites the lead to the canonical "When " before parsing.

No new variant or runtime change — it reuses the existing, runtime-tested TurnFaceUp trigger path.

Verification

• Test: the As-form parses to the same TurnFaceUp trigger + PutCounter effect as the When-form.
• Full engine lib suite green (12420 passed, 0 regressions); clippy -D warnings + parser gate clean.
• Local regen: 4 cards flip to supported, 0 regressions.

Closes #3691

[gemini-code-assist]

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[matthewevans]

VERDICT: request-changes

[HIGH] The PR routes “As … is turned face up” replacement text through triggered-ability parsing. Evidence: crates/engine/src/parser/oracle_trigger.rs rewrites the As lead to When, while the engine already has the correct replacement seam as ReplacementEvent::TurnFaceUp in crates/engine/src/types/replacements.rs; the replacement registry also notes that TurnFaceUp is currently a parser-emitted placeholder in crates/engine/src/game/replacement.rs. Why it matters: Hooded Hydra/Bubble Smuggler/Gift of Doom effects apply as the permanent is turned face up, not later as a stack trigger, so this gives players an illegal response window and models the class at the wrong seam. Suggested fix: parse this class in oracle_replacement.rs as ReplacementEvent::TurnFaceUp and wire the replacement handler/actions instead of classifying it as a trigger.

[matthewevans]

Formalizing my blocking review comment: “As this is turned face up” is being modeled as a trigger, but the rules-correct seam is the TurnFaceUp replacement path.

[philluiz2323]

Re-modeled as a replacement per your review — thanks, you're right that the stack-trigger seam gave an illegal response window.

95f51a245 (branch reset to main, trigger approach discarded):

• Parser (oracle_replacement.rs): parse_turned_face_up_replacement emits ReplacementDefinition(ReplacementEvent::TurnFaceUp){valid_card: SelfRef, execute} (modeled on the as-enters / untap-step replacements); is_replacement_pattern routes the As-led form (the When form stays a trigger).
• Runtime: added ProposedEvent::TurnFaceUp and wired a real applier (replacing the placeholder) — it runs the alternative effect chain bound to the permanent being turned up (source = that object, so the it/SelfRef anaphor binds) and returns the event unchanged (the turn-up still happens). morph::turn_face_up raises it via replace_event after restoring the real face, so the effect applies AS the permanent is turned up — no stack window.
• Tests: parser (As-form → TurnFaceUp replacement + PutCounter execute) and an end-to-end runtime test (a face-down megamorph turned face up gains five +1/+1 counters).

Local regen: 3 cards flip (Hooded Hydra, Bubble Smuggler, Gift of Doom), 0 regressions. Crowd-Control Warden is left for a follow-up — its compound "As ~ enters or is turned face up, put X …" (dual event + dynamic X) is a different pattern. Full engine lib suite green (12451 passed), clippy -D warnings + parser gate clean.

[matthewevans]

VERDICT: request-changes

[HIGH] The new TurnFaceUp applier binds the turned-up permanent as a normal target slot, so the Gift of Doom class still resolves against the wrong object. Evidence: crates/engine/src/game/replacement.rs:2664-2668 builds every replacement execute ability with source_id = object_id and then sets ability.targets = [Object(object_id)]; Effect::Attach resolves the host from ability.targets before falling back to filter resolution in crates/engine/src/game/effects/attach.rs:31-39 and :177-187; and this parser path explicitly includes Gift of Doom in crates/engine/src/parser/oracle_replacement.rs:5032-5055, while the runtime test only covers the Hooded-Hydra counter case in crates/engine/src/game/morph.rs:615-650. Why it matters: As Gift of Doom is turned face up, you may attach it to a creature needs the Aura itself as SelfRef/source, but it still needs a real creature host target or choice; pre-seeding the Aura into explicit target slots makes the host resolver consume the Aura itself instead. Suggested fix: bind only the anaphoric self reference/source to the turned-up permanent, do not stuff it into ordinary target slots, and add a runtime Gift-of-Doom-style test with another legal creature host.

[MED] The new CR annotations cite the wrong rules. Evidence: the new comments use CR 711 + CR 614.12 in crates/engine/src/game/replacement.rs, crates/engine/src/parser/oracle_replacement.rs, crates/engine/src/game/morph.rs, crates/engine/src/types/proposed_event.rs, and related wiring; but the local rules text has CR 614.1e for “As [this permanent] is turned face up ...” replacement effects and CR 708.11 for applying them while the permanent is being turned face up, while CR 614.12 is enters-the-battlefield replacement effects and CR 711 is Leveler Cards. Suggested fix: replace these citations with the verified turn-face-up replacement rules, adding morph/disguise-specific refs only where the code is specifically about those special actions.