fix(engine): keep prepared-copy spells stack-resident through targeting

[nishu-builder]

Summary

Keeps a prepared-copy spell alive while its cast is paused for targeting. CastPreparedCopy created the copy object in Exile with is_token = true and then paused for target selection; a state-based-action pass during the pause removed the token (outside battlefield/stack), and completing ChooseTarget emitted SpellCast against a destroyed object — leaving a stack entry referencing an absent object. Found by an external deterministic-replay harness (11 distinct seeds; repro: a prepared back-face Regrowth copy targeting a graveyard card), with both actions drawn from the engine's own exact legal-action set. The fix aligns the prepared-copy path with ordinary announcement: the copy is stack-resident (same-id StackEntryKind::Spell) from cast start, so CR 704.5d/e token cleanup correctly ignores it, and it ceases to exist through the normal post-resolution route. The residency check requires the same-id entry to be StackEntryKind::Spell specifically — same-id non-spell projections (virtual activated-ability overlays) neither shield an off-battlefield token from SBAs nor bypass the movement guards, with a hostile fixture proving both.

Files changed

• crates/engine/src/game/sba.rs
• crates/engine/src/game/zone_pipeline.rs
• crates/engine/src/game/zones.rs
• crates/engine/tests/integration/issue_1312_prepared_spell_cast_triggers.rs

CR references

• CR 109.1
• CR 601.2a
• CR 602.2a
• CR 603.3
• CR 704.5d
• CR 704.5e

Implementation method (required)

Method: /engine-implementer

Track

Developer

LLM

Model: gpt-5.6-sol
Thinking: high
Tier: Frontier

Verification

• Required checks ran clean, or the exact CI-owned alternative is stated below.

• Gate A output below is for the current committed head.

• Final review-impl below is clean for the current committed head.

• Both anchors cite existing analogous code at the same seam.

• tilt get uiresource clippy — Tilt unavailable in this worktree; used the documented direct fallback.

• cargo fmt --all / cargo fmt --all -- --check — passed.

• git diff --check — passed.

• cargo clippy -p phase-engine --all-targets -- -D warnings — passed on head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b.

• cargo test -p phase-engine — passed on head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b (full suites, 0 failed).

• Plan verification matrix — passed individually: SBA-pass survival regression (production CastPreparedCopy → explicit sba::check_state_based_actions pass mid-targeting → ChooseTarget completes → stack object exists → normal resolution), countered-copy sibling (copy ceases correctly), hostile same-id non-spell fixture (virtual ActivatedAbility overlay does not shield SBA removal nor pass movement guards), raw-movement and zone-pipeline hostile fixtures, three direct-to-stack sibling tests.

• Revert probe — with the raw-zone-only residency check restored, the survival regression fails; with the fix, passes.

• ./scripts/gen-card-data.sh — passed on head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b.

• cargo coverage — passed on head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b: timeless legal 15124/16180 fully supported (93.5%); vintage legal 29841/32268 fully supported (92.5%).

• cargo semantic-audit — passed on head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b: 32732 cards audited, 297 existing findings.

Gate A

Gate A PASS head=f569c3753289f763d95fc7ea5644bdf8ff7b6a5b base=6d7821dced9623609edea342b47dd9c704ff0b36

Anchored on

• crates/engine/src/game/casting.rs:12086 — announce_spell_on_stack binds the spell object's exact id to StackEntryKind::Spell at announcement; the prepared-copy path now establishes the same residency at the same point in its cast.
• crates/engine/src/game/effects/cast_from_zone.rs:933 — cast_single_target_during_resolution's direct-to-stack copy casting is the analogous copy-cast seam whose object lifetime the fix mirrors.

Final review-impl

Final review-impl PASS head=f569c3753289f763d95fc7ea5644bdf8ff7b6a5b

Claimed parse impact

None.

Validation Failures

Contributor-environment note per the engine-implementer skill: pipeline steps ran as isolated fresh contexts (Codex CLI sessions) with artifact-only handoffs rather than spawned Claude subagents. Plan review: 3 rounds to clean (1 → 1 → 0; round one tightened the residency contract to StackEntryKind::Spell against same-id virtual ability overlays, round two corrected the rules rationale to CR 109.1/602.2a/603.3 after an invalid CR 111.1b citation was caught). Implementation review: 1 round, clean.

CI Failures

None.

Related

Same contributor as #6997 (merged), #7007, #7008; independent concerns.

Summary by CodeRabbit

• Bug Fixes

  • Fixed token and card-copy cleanup when objects are associated with spell entries on the stack.
  • Ensured prepared spell copies remain available during target selection and resolve correctly.
  • Prevented tokens linked to activated abilities from being incorrectly treated as spells.
  • Corrected behavior when prepared copies are countered, including proper stack removal and cleanup.

• Tests

  • Added regression coverage for spell copies, activated abilities, targeting, resolution, and countering scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 76f014a8-d62a-4bc8-9f7b-98a5dd98a95f

📥 Commits

Reviewing files that changed from the base of the PR and between acfeaf0 and f569c37.

📒 Files selected for processing (4)

• crates/engine/src/game/sba.rs
• crates/engine/src/game/zone_pipeline.rs
• crates/engine/src/game/zones.rs
• crates/engine/tests/integration/issue_1312_prepared_spell_cast_triggers.rs

---

📝 Walkthrough

Walkthrough

The change makes token and card-copy stack residency state-aware. Matching spell entries preserve announced objects, while activated, triggered, keyword, and unmatched entries do not. Regression tests cover cleanup, movement, resolution, and countered prepared copies.

Changes

Token and copy residency

Layer / File(s)	Summary
State-aware stack residency crates/engine/src/game/zones.rs	object_has_stack_residency recognizes matching Spell entries and excludes ability entries. Token and card-copy predicates use this state-aware check.
Cleanup and zone movement integration crates/engine/src/game/sba.rs, crates/engine/src/game/zone_pipeline.rs, crates/engine/src/game/zones.rs	State-based actions and token movement pass GameState to residency checks. Tests cover matching spell entries, activated abilities, and unmatched objects.
Prepared spell lifecycle coverage crates/engine/tests/integration/issue_1312_prepared_spell_cast_triggers.rs	Prepared-copy tests cover stack persistence, target finalization, normal resolution, countering, and synthetic-copy removal.

Estimated code review effort: 4 (Complex) | ~45 minutes

Suggested labels: bug

Suggested reviewers: matthewevans, lgray

Sequence Diagram(s)

sequenceDiagram
  participant GameState
  participant StateBasedActions
  participant ZonePipeline
  participant Zones
  participant PreparedSpellTest
  GameState->>StateBasedActions: evaluate token and copy cleanup
  StateBasedActions->>Zones: inspect matching stack entry
  GameState->>ZonePipeline: process token zone change
  ZonePipeline->>Zones: validate state-aware residency
  PreparedSpellTest->>GameState: cast prepared copy
  GameState-->>PreparedSpellTest: retain or remove copy based on stack entry

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: keeping prepared-copy spells on the stack during targeting.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

Generated for head f569c3753289f763d95fc7ea5644bdf8ff7b6a5b.

Parse changes introduced by this PR

✓ No card-parse changes detected.

[matthewevans]

[MED] Scope prepared-copy stack residency to the production casting/SBA boundary rather than globally exempting same-ID placeholders. Evidence: crates/engine/src/game/zones.rs:25 now treats any matching StackItem::Spell as residency, while the new regression test manually calls check_state_based_actions during TargetSelection at crates/engine/tests/integration/issue_1312_prepared_spell_cast_triggers.rs:105; normal cast flow reaches state-based actions at the priority boundary (crates/engine/src/game/engine.rs:11051, crates/engine/src/game/engine_priority.rs:180). Why it matters: this global predicate lets an Exile token/copy survive whenever an unrelated same-ID spell placeholder exists, even outside the actual cast lifecycle; the test manufactures that condition before target finalization turns the object into Zone::Stack.

Please remove or rework the global exemption and add a production-path reproduction that advances through the real legal-action/cast flow to the normal SBA boundary. If debug/replay handling needs a special policy, keep it at that explicit API rather than changing the shared zone-residency rule. The revised test should demonstrate both that the prepared copy survives the real targeting path and that the synthetic non-stack case is still cleaned up.