316344 2026-06-04 14:41:04 -0700 [Site Isolation] Enable MultiProcessBackForwardCache in WebKitTestRunner when Site Isolation is enabled 2026-06-04 16:25:47 -0700 1 1 1 Unclassified WebKit Tools / Tests WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 basuke basuke webkit-bug-importer oldest_to_newest 2217742 0 basuke 2026-06-04 14:41:04 -0700 Under Site Isolation, WebProcessPool::createWebPage auto-enables MultiProcessBackForwardCache (and UseUIProcessForBackForwardItemLoading) at page creation. WebKitTestRunner applies a full preference set per test (resetPreferencesToConsistentValues -> WKPreferencesResetTestRunnerOverrides), resetting unspecified preferences to their defaults and clobbering that runtime flip. As a result, BFCache-under-Site-Isolation layout tests run with MultiProcessBackForwardCacheEnabled=false, so BackForwardCache::addIfCacheable's guard (siteIsolationEnabled() && !multiProcessBackForwardCacheEnabled()) rejects caching and back/forward restore fails (e.g. fast/events/event-timing-back-forward-cache-duration.html under the mac-site-isolation suite). Mirror the product coupling in WebKitTestRunner: when SiteIsolationEnabled is set, also enable MultiProcessBackForwardCacheEnabled. Add a same-origin Site-Isolation copy of the event-timing test as a regression guard. UseUIProcessForBackForwardItemLoading coupling is deferred; enabling it surfaces a separate nested-frame form-state restoration failure. 2217745 1 basuke 2026-06-04 14:49:51 -0700 <rdar://problem/178760818> 2217746 2 basuke 2026-06-04 14:50:11 -0700 Pull request: https://github.com/WebKit/WebKit/pull/66491 2217788 3 ews-feeder 2026-06-04 16:25:45 -0700 Committed 314591@main (49a03a1fa5d5): <https://commits.webkit.org/314591@main> Reviewed commits have been landed. Closing PR #66491 and removing active labels.