fix(engine): drop never-gated hidden array items instead of null holes

[guitavano]

Summary

Same fix as the blocks runtime, ported to the deco engine.

Hiding an array item wraps it in a multivariate flag gated by a never matcher. blocks/flag.ts returns match?.value → undefined when no variant matched. The engine's resolvePropsWithHints wrote that undefined back into the resolved array (mutableProps[index] = undefined), leaving a hole that serializes to null in JSON and renders as an empty card (blank benefit rows, empty banners, etc.).

Fix (engine/core/resolver.ts)

Compact undefined out of resolved arrays before returning. A resolver returning null is a legitimate value and is kept — only the undefined "not present" sentinel is filtered.

Testing

Reproduced empirically first (array with a resolver returning undefined → serialized to [...,null,null]), then confirmed the fix drops the holes.

Added a regression step to engine/core/mod.test.ts (drops hidden array items (resolver -> undefined) but keeps null). Full resolve suite: 8/8 steps pass. deno fmt/deno lint clean.

🤖 Generated with Claude Code

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Summary by cubic

Drop hidden array items in the engine instead of leaving null holes. Prevents empty cards from undefined entries and skips extra work when arrays have no hidden items.

• Bug Fixes
  • Compact undefined from resolved arrays; only reallocate if the array contains undefined. Preserve null.
  • Broadened tests: all-hidden arrays resolve to [], nested arrays drop hidden items, and null is kept.

^{Written for commit a6f2afd. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes

  • Fixed array property resolution to drop elements that resolve to undefined, avoiding empty slots in results.
  • Preserved explicitly resolved null values so they remain intact in array outputs.

• Tests

  • Added additional test coverage for hidden/omitted items within arrays, including nested arrays and the case where all elements are hidden.

[github-actions]

Tagging Options

Should a new tag be published when this PR is merged?

• 👍 for Patch 1.202.2 update
• 🎉 for Minor 1.203.0 update
• 🚀 for Major 2.0.0 update

[coderabbitai]

📝 Walkthrough

Walkthrough

Array resolution now removes undefined results from untyped arrays while preserving null, including nested arrays. Tests cover mixed, all-hidden, and nested array results.

Changes

Array resolution

Layer / File(s)	Summary
Filter undefined array results engine/core/resolver.ts, engine/core/mod.test.ts	Untyped array results filter out undefined elements while preserving null; tests cover mixed, all-hidden, and nested arrays.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main fix: compacting hidden array items instead of leaving null-like holes.

✨ 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 guitavano/fix-never-matcher-null-array

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[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}