chore: Fail fast for migration DTO null contracts

[hatayama]

Summary

• Align third-party tool migration DTOs with their existing non-null contracts.
• Add pinning tests so invalid internal calls fail fast instead of being silently normalized.

User Impact

• No supported migration workflow changes for valid projects.
• Invalid internal migration data now surfaces immediately during development instead of being converted to empty values.

Changes

• Replace migration rule data null fallbacks with ArgumentNullException after the existing Debug.Assert contracts.
• Make migration file path snapshots reject null while keeping the empty-array fast path.
• Add focused EditMode tests for the rule data and preview/result null contracts.

Verification

• dist/darwin-arm64/uloop compile --project-path "$(git rev-parse --show-toplevel)" (0 errors, 0 warnings)
• dist/darwin-arm64/uloop run-tests --project-path "$(git rev-parse --show-toplevel)" --test-mode EditMode --filter-type exact --filter-value "io.github.hatayama.UnityCliLoop.Tests.Editor.ThirdPartyToolMigrationRulesTests" (164 passed)
• dist/darwin-arm64/uloop run-tests --project-path "$(git rev-parse --show-toplevel)" --test-mode EditMode --filter-type exact --filter-value "io.github.hatayama.UnityCliLoop.Tests.Editor.ThirdPartyToolMigrationFileServiceTests" (133 passed, 4 skipped)
• dist/darwin-arm64/uloop run-tests --project-path "$(git rev-parse --show-toplevel)" --test-mode EditMode --filter-type regex --filter-value "(RemovedLegacyPlayerLoopTimingSignature_WhenOriginalParametersIsNull_Throws|RemovedLegacyPlayerLoopTimingSignature_WhenRemovedParametersIsNull_Throws|ThirdPartyToolMigrationContentResult_WhenContentIsNull_Throws|ThirdPartyToolMigrationContentResult_WhenRemovedSignaturesIsNull_Throws|ThirdPartyToolMigrationPreview_WhenFilePathsIsNull_Throws|ThirdPartyToolMigrationResult_WhenFilePathsIsNull_Throws)" (6 passed)

[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

Run ID: 2fd837c0-e975-4153-9ae7-996bb53d7b9a

📥 Commits

Reviewing files that changed from the base of the PR and between 071fd76 and c69749f.

📒 Files selected for processing (4)

• Assets/Tests/Editor/ThirdPartyToolMigrationFileServiceTests.cs
• Assets/Tests/Editor/ThirdPartyToolMigrationRulesTests.cs
• Packages/src/Editor/Domain/ThirdPartyToolMigrationData.cs
• Packages/src/Editor/Domain/ThirdPartyToolMigrationRuleData.cs

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📝 Walkthrough

Walkthrough

Constructors and copy logic in third-party tool migration domain classes now throw ArgumentNullException for null arguments (filePaths, originalParameters, removedParameters, content, removedPlayerLoopTimingSignatures) instead of substituting empty defaults. Corresponding unit tests were added to verify this fail-fast behavior.

Changes

Fail-fast validation for migration domain objects

Layer / File(s)	Summary
File path snapshot copy validation Packages/src/Editor/Domain/ThirdPartyToolMigrationData.cs, Assets/Tests/Editor/ThirdPartyToolMigrationFileServiceTests.cs	Copy(string[] filePaths) now throws ArgumentNullException for null input rather than returning an empty array; empty arrays still return Array.Empty<string>(). New tests assert ThirdPartyToolMigrationPreview and ThirdPartyToolMigrationResult throw on null filePaths.
Rewrite rule constructor validation Packages/src/Editor/Domain/ThirdPartyToolMigrationRuleData.cs, Assets/Tests/Editor/ThirdPartyToolMigrationRulesTests.cs	RemovedLegacyPlayerLoopTimingSignature and ThirdPartyToolMigrationContentResult constructors now throw ArgumentNullException for null originalParameters, removedParameters, content, and removedPlayerLoopTimingSignatures instead of defaulting to empty values. New tests added along with a using System; directive.

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

Possibly related PRs

• hatayama/unity-cli-loop#1540: Prior PR that introduced the same fail-fast ArgumentNullException pattern in these same domain constructors and their tests.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: failing fast on null migration DTO contracts.
Description check	✅ Passed	The description is directly related to the code changes and test updates in this pull request.
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 chore/fail-fast-migration-dto-null-contracts

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[cubic-dev-ai]

No issues found across 4 files

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