Prevent WAN cache invalidation from purging concurrent refreshes

[Copilot]

Namespace definition invalidation touched the WAN check key and then deleted the cached value. A refresh completing between those operations could be immediately discarded.

Changes

• Invalidation

  • Rely exclusively on touchCheckKey() for cross-server invalidation.
  • Remove the redundant value-key deletion and its race window.
  • Continue clearing request-local memoized definitions.

• Concurrency coverage

  • Verify stale fills racing invalidation are rejected after WAN holdoff.
  • Verify fresh fills completing during invalidation remain cached.
  • Exercise the production hotTTR, lockTSE, and cache-version options.

public function invalidate(): void {
	$this->cache->touchCheckKey( $this->getCheckKey() );
	$this->loaded = false;
	$this->memoizedDefinitions = [];
}

• Documentation
  • Clarify that namespace saves invalidate through the WAN check key.

[Copilot]

Pull request overview

This PR removes a race window in NamespaceRepository::invalidate() where a concurrent WANObjectCache refresh could complete between “touch check key” and “delete value key” and then be immediately discarded. The change makes invalidation rely solely on the WAN check key (while still clearing request-local memoization) and adds integration tests to exercise the concurrency behavior.

Changes:

• Remove value-key deletion from NamespaceRepository::invalidate() and rely on touchCheckKey() for cross-server invalidation.
• Add integration tests covering stale cache fills racing invalidation (rejected after holdoff) and fresh fills completing during invalidation (remain cached), using hotTTR, lockTSE, and cache version.
• Update README to clarify that namespace saves invalidate via the WAN check key.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/NamespaceRepository.php	Removes value-key deletion during invalidation to eliminate the refresh race window and rely on check-key invalidation.
tests/phpunit/integration/NamespaceRepositoryTest.php	Adds concurrency-focused integration tests that simulate racing fills/invalidation using WANObjectCache behavior.
README.md	Updates documentation to match the new invalidation behavior (check key only).