fix(engine): parse and resolve Nether Spirit's dropped self-reanimation intervening-if

[rykerwilliams]

Summary

Nether Spirit ({1}{B}{B}, Tempest): "At the beginning of your upkeep, if this card is the only creature card in your graveyard, you may return this card to the battlefield."

The intervening-if was dropped entirely by the parser (condition: null in card-data.json). split_trigger splits Oracle text at the first unrecognized comma; since "At the beginning of your upkeep" has no comma, the whole "if this card is the only creature card in your graveyard, you may return this card to the battlefield" fell through to the effect side untouched — there was no combinator in parse_remaining_state_presence_conditions recognizing "~ is the only <type> [card] in <zone>". That also left trigger_zones stuck at the structural default ["Battlefield"] (making the trigger undetectable while the card sits in the graveyard) and ChangeZone.origin null.

• Adds parse_source_is_only_type_in_zone (oracle_nom/condition.rs), composed entirely from existing building blocks (parse_source_self_token, parse_type_phrase, an ObjectCount == 1 QuantityComparison). When the type-phrase filter carries a non-battlefield zone, wraps the condition in StaticCondition::And{[SourceInZone{zone}, quantity]} so the existing, unmodified trigger_condition_source_zones walker auto-derives trigger_zones/ChangeZone.origin — zero runtime code changed. Precedent: Jocasta, Automaton Avenger already drives the identical And{SourceInZone, ...} derivation end-to-end.
• Removes a stale game/coverage.rs exclusion that was silencing the semantic auditor for this exact bug (confirmed via card-data.json scan: the excluded substring matches exactly this one card).

CR 603.4 (intervening-if, checked at trigger time and re-checked at resolution), CR 113.6 / CR 113.6b (ability functions off-battlefield only from the zone it states).

Test plan

• 3 new parser unit tests (condition.rs): graveyard form → And[SourceInZone(Graveyard), ObjectCount==1]; battlefield form → bare QuantityComparison (no spurious SourceInZone); rejection guard (no "only" → parse error)
• Parser-shape test (oracle_trigger_tests.rs): asserts condition.is_some(), trigger_zones == [Graveyard], ChangeZone.origin == Some(Graveyard) for Nether Spirit's verbatim Oracle text
• 6 integration tests (nether_spirit_only_creature_card_intervening_if.rs) driving the real process_triggers/stack::resolve_top pipeline: does-not-fire with 2 creature cards, positive reach-guard, fires-and-returns when sole, decline leaves it in graveyard, CR 603.4 resolution-time recheck fizzles when a 2nd creature card enters in response, two-copies-neither-fires
• Live-revert-and-rerun proof: disabling the new combinator's registration reproduces failure in the parser-shape test and 4/6 integration tests (2 negative-guard tests pass vacuously as expected, guarded by the positive reach-guard test)
• cargo fmt --all, parser combinator gate, CR-annotation gate all pass
• cargo clippy -p engine --lib --tests -- -D warnings clean
• Full cargo test -p engine --lib (16687+ tests) and --test integration green after rebase onto current main

[gemini-code-assist]

Code Review

This pull request implements parsing and runtime support for Nether Spirit's intervening-if condition ("~ is the only [card] in "). It introduces the parse_source_is_only_type_in_zone parser, which correctly hoists off-battlefield zones into a SourceInZone conjunct to allow proper trigger detection and zone origin derivation. Comprehensive unit and integration tests are added to verify the behavior. The reviewer suggests simplifying the parser's return statement by returning the parsed remainder subslice directly instead of calculating a consumed offset via pointer arithmetic.

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[gemini-code-assist]

Calculating the consumed offset via pointer arithmetic is unnecessary here because remainder is already a valid subslice of input with the correct lifetime. Returning remainder directly is safer, cleaner, and more idiomatic.

    Ok((remainder, condition))

[github-actions]

Parse changes introduced by this PR · 1 card(s), 3 signature(s) (baseline: main 674af5650599)

1 card(s) · ability/ChangeZone · field from: ∅ → graveyard

Examples: Nether Spirit

1 card(s) · trigger/Phase · field active in: battlefield → graveyard

Examples: Nether Spirit

1 card(s) · trigger/Phase · field condition: ∅ → source is in graveyard and # of in graveyard you control creature = 1

Examples: Nether Spirit

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

[matthewevans]

Verdict: Approved

🔴 Blocker

None.

🟡 Non-blocking

None.

✅ Clean

• The condition is parsed at the existing state-condition authority and uses the established ObjectCount == 1 plus SourceInZone representation, allowing existing trigger-zone and return-origin derivation to do the runtime work.
• The current parse diff is exactly one card, Nether Spirit: condition, active trigger zone, and ChangeZone origin all move from absent/default state to the intended graveyard semantics.
• The registered integration suite reaches trigger collection, the intervening-if fire-time and resolution-time checks, the optional choice, and the graveyard-to-battlefield move. The reviewer-requested direct remainder return is included in the current head.

Recommendation: approved and queued for merge.