fix(engine): Mockingbird copy ceiling uses cast-payment stamp (#6440)

[claytonlin1110]

Summary

• Mockingbird-class AmountSpentToCastSource copy ceilings now read the entering object's mana_spent_to_cast_amount via the same objects→liminal dual lookup used for source identity (CR 400.7d).
• Uncast put-onto-battlefield (Chord of Calling) yields Some(0) instead of unconstrained None, so MV 2+ creatures are no longer legal copy targets.
• PendingSpellResolution.actual_mana_spent is no longer consulted for this ceiling (hostile unit fixture proves Chord's payment cannot override the stamp).

Closes #6440

Test plan

• cargo fmt --all
• Unit: issue_6440_* (4) + typed_copy_limit_zero_stamp_is_some_zero_not_unconstrained
• Integration: issue_6440_mockingbird_* (chord uncast, cast path, clone sibling, parse reach-guard)
• CI clippy / test-engine

Validation Failures

Plan review completed clean via isolated agents (2 rounds). Implementation and /review-impl subagents could not be spawned (API usage limit); implementation was done in the orchestrator thread against the approved plan. Isolated implementation review did not run — please give the PR an extra human/architecture pass before merge.

Summary by CodeRabbit

• Bug Fixes

  • Fixed copy effects that rely on mana spent to cast a creature so uncast entries are constrained to a maximum mana value of zero (instead of being treated as unconstrained).
  • Copy mana-value ceilings are now taken from the entering object’s cast-payment “stamp,” including when the stamp is zero and for liminal entries; Clone without a limit remains unrestricted.

• Tests

  • Added regression coverage for Mockingbird via Chord of Calling (uncast vs cast), and for Clone behavior, plus a new unit test covering the zero-stamp ceiling behavior.

[coderabbitai]

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ℹ️ Recent review info

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Run ID: 5830df47-80a8-4ccd-8a0d-701a500babab

📥 Commits

Reviewing files that changed from the base of the PR and between 155828c and 7b552b9.

📒 Files selected for processing (1)

• crates/engine/tests/integration/main.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/engine/tests/integration/main.rs

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📝 Walkthrough

Walkthrough

Mockingbird copy targeting now uses the entering object’s cast-payment stamp, including zero for uncast entries, instead of unrelated spell-resolution mana. Unit and integration tests cover cast, uncast, liminal, Clone, and parsing behavior.

Changes

Copy ceiling correction

Layer / File(s)	Summary
Copy ceiling semantics crates/engine/src/ai_support/copy.rs	Documentation and unit coverage define Some(0) as the constrained result for an AmountSpentToCastSource limit with a zero stamp.
Replacement-effect stamp propagation crates/engine/src/game/engine_replacement.rs	apply_post_replacement_effect extracts the entering object’s cast-payment stamp, including liminal objects, and uses it for BecomeCopy target limits.
Mockingbird integration coverage crates/engine/tests/integration/issue_6440_mockingbird_uncast_copy_ceiling.rs, crates/engine/tests/integration/main.rs	Integration tests cover uncast and cast Mockingbird behavior, Clone’s unconstrained behavior, oracle parsing, and test-module registration.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Possibly related PRs

• phase-rs/phase#6352: Both changes address cast-payment stamp propagation for copy-related effects.
• phase-rs/phase#6539: Both modify shared copy-choice and replacement-effect handling.

Suggested reviewers: matthewevans

Sequence Diagram(s)

sequenceDiagram
  participant apply_post_replacement_effect
  participant EnteringObject
  participant copy_target_mana_value_ceiling
  participant CopyTargetChoice
  apply_post_replacement_effect->>EnteringObject: read mana_spent_to_cast_amount
  EnteringObject-->>apply_post_replacement_effect: return cast-payment stamp
  apply_post_replacement_effect->>copy_target_mana_value_ceiling: calculate BecomeCopy max_mana_value
  copy_target_mana_value_ceiling-->>apply_post_replacement_effect: return Some(stamp) or None
  apply_post_replacement_effect->>CopyTargetChoice: apply copy target limit

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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 summarizes the main fix for Mockingbird's copy ceiling bug.
Linked Issues check	✅ Passed	The changes directly address #6440 by using the entering object's cast-payment stamp and adding regression coverage for the Chord of Calling case.
Out of Scope Changes check	✅ Passed	The added documentation, internal rename, and tests all support the reported Mockingbird copy-ceiling fix and do not appear unrelated.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

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• Create PR with unit tests

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[github-actions]

Parse changes introduced by this PR

✓ No card-parse changes detected.

[matthewevans]

Current-head maintainer review complete. The replacement seam derives the Mockingbird ceiling from the entering object’s cast provenance, while the registered Chord → uncast/cast/recast regression covers the lifecycle and leaves copy behavior unchanged. No further findings.

[matthewevans]

Current-head maintainer re-review complete. This port contains current main plus both independent integration module registrations; it does not alter the Mockingbird lifecycle behavior or its regression coverage. No further findings.