feat(parser): peel a leading supertype off "<Supertype> <Subtype>" subjects

[minion1227]

CR 205.4a + CR 205.3m

Bug

A subject phrase like "Legendary Humans you control" names the legendary supertype plus the Human subtype — but the shared subtype authority typed_filter_for_subtype treated the whole two-word string as one subtype and fabricated Subtype("Legendary Human"), a filter that matches no card in existence. The anthems therefore applied to nothing at runtime:

• General's Enforcer — Legendary Humans you control have indestructible.
• Kashi-Tribe Elite — Legendary Snakes you control have shroud.

Before: affected = [Creature, Subtype("Legendary Human")] (zero matches).
After: affected = [Creature, Subtype("Human")] + HasSupertype(Legendary).

Fix

At the single authority typed_filter_for_subtype (grammar.rs): peel a leading supertype word ("Legendary"/"Snow"/"Basic"/…) via a new split_leading_supertype helper, attach it as FilterProp::HasSupertype, and resolve the remainder as the real subtype (recursing so the core-type inference still runs on the true subtype).

Because every capitalized-subtype fallback in the subject parsers routes through this one function, all four call sites — parse_typed_you_control's creature-arm and combat-status-prefix arm, plus the parse_creature_subject_filter fallback — inherit the fix from one place.

Why it's the right seam / minimal blast radius

• One authority, not four sibling patches — the fix lands where the fabrication happens, so the whole <supertype> <subtype> subject class is covered in a single change.
• A bare supertype ("Legendary creatures") already routes through its own path (descriptor_is_supertype) and is untouched; a plain subtype ("Goblins") gains no supertype property (regression-tested).
• split_leading_supertype returns None for a bare supertype (no following subtype), so it never strips a legitimate lone supertype.

Tests

• legendary_subtype_subject_peels_supertype_and_keeps_subtype — end-to-end via parse_static_line: General's Enforcer → Subtype("Human") + HasSupertype(Legendary) + AddKeyword(Indestructible).
• typed_filter_for_subtype_peels_leading_supertype — building-block: "Legendary Human" → Human + HasSupertype(Legendary); "Goblin" → Goblin, no supertype (regression).
• Full parser::oracle_static::tests (1039 passed, 0 failed), including the existing bare-supertype "Legendary creatures" / Jodah tests.

CR verification

• CR 205.4a — the supertypes (basic, legendary, ongoing, snow, world) — verified in docs/MagicCompRules.txt.
• CR 205.3m — subtype recognition on the remainder.

AI-contributor notes

• Rules-correct: the anthem now targets legendary creatures of the named subtype per CR 205.4a; the enchanted/controlled set is real, not empty.
• Builds the class: the fix is at the shared subtype authority, so any <supertype> <subtype> subject (current or future) is covered.
• Verified: live-parsed General's Enforcer and Kashi-Tribe Elite before/after against Scryfall Oracle text; cargo fmt, CI-exact clippy -p engine --all-targets --features proptest -D warnings, and the full oracle_static test module are green.

🤖 Generated with Claude Code

[gemini-code-assist]

Warning

You have reached your daily quota limit. Please wait up to 24 hours and I will start processing your requests again!

[matthewevans]

✅ Architecturally clean, correct building-block fix — holding formal approval for CI.

✅ Clean

• Right seam. The supertype-peel lives in typed_filter_for_subtype (grammar.rs), the single subtype-filter authority, so every <supertype> <subtype> compound benefits — not just the two cards cited. Recursing into typed_filter_for_subtype(rest) composes cleanly rather than special-casing.
• Reuses the existing combinator. split_leading_supertype delegates to nom_target::parse_supertype_word instead of hand-rolling supertype matching; the original-case remainder uses the documented descriptor[len − rest_lower.len()..] offset idiom.
• CR + cards verified. CR 205.4a grep-confirmed verbatim ("supertypes are basic, legendary, ongoing, snow, and world"); CR 205.3m confirms Human/Snake are subtypes. General's Enforcer — "Legendary Humans you control have indestructible." — and Kashi-Tribe Elite — "Legendary Snakes you control have shroud." — both match Scryfall. This is the fabricated zero-match Subtype("Legendary Human") class fixed at the source.
• Discriminating tests at both levels: the building-block test asserts the peel plus a plain-Goblin negative (no fabricated supertype), and the integration test locks HasSupertype(Legendary) + Subtype(Human) + the anthem AddKeyword modification.

Recommendation: approve as bug once CI settles green on a rebased head (currently BEHIND, CI pending). No changes requested.

[github-actions]

Parse changes introduced by this PR · 2 card(s), 2 signature(s) (baseline: main 67607fd8e8b8)

1 card(s) · static/Continuous · field affects: you control creature Legendary Human → legendary you control creature Human

Examples: General's Enforcer

1 card(s) · static/Continuous · field affects: you control creature Legendary Snake → legendary you control creature Snake

Examples: Kashi-Tribe Elite

1 card(s) had Oracle-text changes (errata/reprint) — excluded as non-parser.

[matthewevans]

✅ Approving — CI resolved green, merge state CLEAN. Correctness verified in the prior review (CR 205.4a supertype handling at the single subtype/type authority, reuses parse_supertype_word, discriminating tests). The head that went green is the reviewed head; enqueuing as bug.