fix(engine): atomically install optional effect prompts

[matthewevans]

Closes #6867

Installs optional-effect direct-choice frames together with their matching prompt, validating the pair before either reaches live state. Adds a regression for atomic rejection of a second optional direct-choice owner.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of optional-effect choices during game resolution.
  • Invalid or conflicting choice transitions now fail safely without changing the active prompt or resolution state.
  • Preserved pending event information when resuming interrupted effect resolution.
• Tests
  • Added coverage for conflicting optional-choice owners and confirmed that game state remains unchanged when such conflicts occur.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 78d64a3c-00b6-433b-b1b6-0bc7c5c96d0f

📥 Commits

Reviewing files that changed from the base of the PR and between a17cec8 and 0e9d93a.

📒 Files selected for processing (1)

• crates/engine/src/game/engine.rs

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: 1bfe6715-3660-4acc-977b-32f3c493698d

📥 Commits

Reviewing files that changed from the base of the PR and between ad7ba57 and a17cec8.

📒 Files selected for processing (3)

• crates/engine/src/game/effects/mod.rs
• crates/engine/src/types/game_state.rs
• crates/engine/tests/integration/cr733_resolved_frame_transition.rs

---

📝 Walkthrough

Walkthrough

The engine adds atomic installation for direct-choice resolution frames. Optional effects use this method and convert installation failures to EffectError::InvalidParam. Integration tests verify that duplicate direct-choice owners preserve the existing stack and prompt.

Changes

Direct-choice installation

Layer / File(s)	Summary
Frame installation contract crates/engine/src/types/game_state.rs	GameState::install_direct_choice_frame validates direct-choice frames, updates WaitingFor, applies the transition, and restores the previous prompt on failure.
Optional-effect integration and regression coverage crates/engine/src/game/effects/mod.rs, crates/engine/tests/integration/cr733_resolved_frame_transition.rs	Optional effects use atomic frame installation and preserve continuation context. Tests verify rejection of a second direct-choice owner with unchanged state.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• phase-rs/phase#5866: Both changes cover optional direct-choice resolution and waiting-state handling.
• phase-rs/phase#6585: Both changes modify optional-effect direct-choice resolution.

Suggested labels: bug, quality

Suggested reviewers: jacobwoodson, lgray

🚥 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 summarizes the main change: atomic installation of optional-effect prompts.
Linked Issues check	✅ Passed	The PR addresses issue #6867 by preventing OptionalEffect PromptMismatch states through atomic frame and prompt installation.
Out of Scope Changes check	✅ Passed	The implementation and regression test directly support the linked crash fix and contain no unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ship/fix-engine-atomically-install-optional-effect-prompts

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[github-actions]

Generated for head 0e9d93adcce778aec66da2ed165aa8d1b50bab47.

Parse changes introduced by this PR

✓ No card-parse changes detected.