fix(ai): filter target-dependent optional costs

[matthewevans]

Summary by CodeRabbit

• Bug Fixes
  • Improved decision validation for effects involving optional costs and deferred targets.
  • Optional payments that enable valid targets are now offered correctly.
  • Optional payments are excluded when declining them would leave no legal targets.
  • Added validation coverage for required casting conditions and target-dependent choices.

[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: 5cd4b382-d170-4bce-a5df-959106b27e69

📥 Commits

Reviewing files that changed from the base of the PR and between 6bfca3f and 252133a.

📒 Files selected for processing (3)

• crates/engine/src/ai_support/context.rs
• crates/engine/tests/integration/ai_decision_contract.rs
• crates/engine/tests/integration/main.rs

💤 Files with no reviewable changes (1)

• crates/engine/src/ai_support/context.rs

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📝 Walkthrough

Walkthrough

AiDecisionContract::issue now validates optional-cost choices that can defer target selection. An integration test verifies that choices leaving no legal targets are excluded.

Changes

Deferred Target Validation

Layer / File(s)	Summary
Reducer validation predicate and issuance crates/engine/src/ai_support/context.rs	AiDecisionContract::issue now validates target-dependent payment changes and deferred target selection during optional-cost decisions.
Deferred optional-cost integration coverage crates/engine/tests/integration/ai_decision_contract.rs, crates/engine/tests/integration/main.rs	The integration test verifies the rejected non-kicker branch and confirms that the contract exposes only the target-enabling kicker payment choice. The test module is registered in the integration suite.

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

Possibly related PRs

• phase-rs/phase#6829: This PR extends the same AiDecisionContract::issue reducer-validation logic.
• phase-rs/phase#7104: Both PRs update AiDecisionContract::issue for target-dependent payment and optional-cost decisions.

Suggested labels: bug

Suggested reviewers: lgray, nishu-builder, invalidcards

🚥 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 main change: filtering optional costs that depend on target legality.
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 docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ship/ai-optional-cost-targets

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/engine/src/ai_support/context.rs`:
- Around line 371-494: Move the regression test
decision_contract_filters_optional_cost_that_leaves_no_legal_targets from
context.rs into the appropriate crates/engine/tests/integration/ test module,
preserving both reach-guard assertions and its existing production cast/contract
behavior. Register the new integration test module through
tests/integration/main.rs as required.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 4b51ab31-9b08-4557-a295-d94928e12540

📥 Commits

Reviewing files that changed from the base of the PR and between d46667f and 6bfca3f.

📒 Files selected for processing (1)

• crates/engine/src/ai_support/context.rs

[github-actions]

Generated for head 252133ae569453efe491e4f06d718107be30fbfe.

Parse changes introduced by this PR

✓ No card-parse changes detected.