LEGLINK-908: Avoid cache key collisions in Validation

[johnbritton]

🛠️ Description of Changes

Objects.hash returns a 32-bit int, so the key space is 2^32. Two different (codeSystem, code, display, valueSetUrl) tuples that hash to the same value share a cache entry, and the second lookup silently receives the first tuple's CodeValidationResult.

This PR replaces the hash with a delimiter-joined string key (codeSystem|code|display|valueSetUrl).

🧪 Testing Performed

Configured validation for remote terminology lookup and ran automated tests.

🧑‍🔬 Unit Testing

• I have written or updated unit tests to cover my changes
• Coverage: 100.0%

📓 Documentation Updated

N/A

Summary by CodeRabbit

• Bug Fixes
  • Improved validation and lookup caching to reliably distinguish different input combinations, including null, empty, and literal “null” values.
  • Ensured negative validation results are cached correctly while null results are not stored.
  • Improved cache consistency across supported caching backends.
• Tests
  • Added coverage for cache key uniqueness, repeated lookups, backend storage, and worker-thread cache resolution.

[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: 197d4a6b-a922-4ce8-b88e-3128eebaebf8

📥 Commits

Reviewing files that changed from the base of the PR and between e54a921 and 48c86c6.

📒 Files selected for processing (2)

• Java/validation/src/main/java/com/lantanagroup/link/validation/providers/ValidationCacheService.java
• Java/validation/src/test/java/com/lantanagroup/link/validation/providers/ValidationCacheServiceCachingTest.java

Included review availability: Your plan includes up to 1 review per rolling hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

ValidationCacheService now builds structured cache keys for validation and lookup operations. Tests cover key uniqueness, null handling, backend storage, result caching, and threaded cache access.

Changes

Validation cache keys

Layer / File(s)	Summary
Structured cache-key integration Java/validation/src/main/java/com/lantanagroup/link/validation/providers/ValidationCacheService.java	Validation and lookup cache keys now use a shared builder with explicit null markers and length-prefixed non-null values.
Cache behavior validation Java/validation/src/test/java/com/lantanagroup/link/validation/providers/ValidationCacheServiceCachingTest.java	Tests cover distinct keys, Caffeine and Redis storage, negative and null result caching, repeated lookups, threaded access, and Spring cache configuration.

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

Merge Risk: ⚪ Minimal · up to 48c86

The change makes validation cache keys specific to their input tuple and adds unit coverage; no actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: seanmcilvenna

🚥 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.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing validation cache key collisions.
Description check	✅ Passed	The description covers the changes, testing, unit tests, coverage, and documentation status.

✨ 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 users/jbritton/LEGLINK-908

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