Expand singleflight boundary in ValidatingCache.Get to cover full hit+check and miss+load path

[yrobla]

Summary

Move the singleflight.Do boundary to wrap the entire Get operation rather than only the miss+load path. This coalesces concurrent liveness checks for the same key into a single storage.Load round-trip, reducing storage pressure under concurrent access.

With only one goroutine running per key at a time, concurrent Gets no longer race with each other. However, concurrent Set calls still happen outside the singleflight boundary, so the miss path retains ContainsOrAdd (not plain Add) to preserve writer-wins semantics: if a Set stores a fresher value while load() is in-flight, that value wins and is returned instead of the loaded one.

Behavior change: an expired cache hit now evicts the entry and falls through to load within the same singleflight operation, returning the fresh value (ok=true) instead of (zero, false). This is a fix: the previous behavior silently dropped a loadable value and forced callers to retry blind.

Fixes #4729

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

Changes

File	Change

Does this introduce a user-facing change?

Yes — Get on an expired entry now returns the freshly loaded value (ok=true) instead of (zero, false). Callers that were checking ok=false to detect expiry and re-calling Get will now receive the value on the first call.

[Copilot]

Pull request overview

This PR expands the singleflight boundary in ValidatingCache.Get so that the entire hit+check and miss+load paths are coalesced per key, aiming to reduce duplicate liveness checks / storage round-trips under concurrency.

Changes:

• Move singleflight.Do to wrap the full Get operation (hit validation + miss load).
• Simplify the miss-store path by replacing ContainsOrAdd + race-handling with a plain Add, and remove the struct-level onEvict field used for discarded-load cleanup.
• Update/replace unit tests to reflect new “expired hit falls through to load” behavior and to add a concurrency dedup test.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
pkg/cache/validating_cache.go	Wrap full Get in singleflight and simplify the miss store path.
pkg/cache/validating_cache_test.go	Update expired-hit expectations and replace a prior race test with a concurrent liveness-check dedup test.

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[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.06%. Comparing base (5e1e1d5) to head (c77a110).

Files with missing lines	Patch %	Lines
pkg/cache/validating_cache.go	87.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4798      +/-   ##
==========================================
- Coverage   69.09%   69.06%   -0.03%     
==========================================
  Files         530      530              
  Lines       55191    55202      +11     
==========================================
- Hits        38136    38128       -8     
- Misses      14134    14156      +22     
+ Partials     2921     2918       -3     

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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