317229 2026-06-16 13:01:32 -0700 [NavigationScheduler] history.back/forward/go(n) coalescing across processes via UIProcess session history traversal queue 2026-07-02 14:41:21 -0700 1 1 1 Unclassified WebKit WebCore Misc. WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 basuke basuke webkit-bug-importer oldest_to_newest 2221279 0 basuke 2026-06-16 13:01:32 -0700 Follow-up to https://bugs.webkit.org/show_bug.cgi?id=317077. Per HTML spec, history.back/forward/go(n) appends a task to the top-level traversable's session history traversal queue. The previous fix (bug 317077) implemented per-WebProcess coalescing by forwarding to the top frame's NavigationScheduler when reachable in this WebProcess. Under Site Isolation, when the top frame is a RemoteFrame (a cross-site iframe initiates the traversal), the queue must live above any single WebProcess. Symptom: - iframe (process A) history.back(); and main frame (process B) history.forward(); queued synchronously do not coalesce; both navigations execute and the user sees an extra load event the spec says should not occur. Proposal: Introduce SessionHistoryTraversalQueue, owned by WebPageProxy (top-level traversable proxy). WebProcess NavigationScheduler routes to it via a new IPC when the top frame is a RemoteFrame. The queue accumulates pending delta and flushes on a 0-delay timer, calling goToBackForwardItemAtIndex with the net delta (no-op when delta == 0, matching "going nowhere"). Class naming leaves room for a future spec-faithful "sequential apply + synchronous queue jumping" implementation as a separate epic. Out of scope for this bug: spec-correct top-level reload semantics for history.go(0) (currently per-frame reload — see related followup). Test plan: - API tests covering cross-process iframe <-> main frame coalescing under Site Isolation enabled. - WPT suites under imported/w3c/web-platform-tests/html/browsers/browsing-the-web/overlapping-navigations-and-traversals/ with SI configuration. Local prototype on branch eng/basuke/cross-process-traversal-queue already passes a SiteIsolation.CrossProcessHistoryTraversalCoalesce API test; bug 317077 API/WPT do not regress. 2221778 1 basuke 2026-06-17 15:41:29 -0700 <rdar://problem/179574582> 2221780 2 basuke 2026-06-17 15:41:52 -0700 Pull request: https://github.com/WebKit/WebKit/pull/67386 2222494 3 basuke 2026-06-20 07:24:23 -0700 <rdar://problem/179641336> 2224332 4 basuke 2026-06-26 16:14:41 -0700 Pull request: https://github.com/WebKit/WebKit/pull/67459 2224367 5 basuke 2026-06-26 17:39:28 -0700 <rdar://problem/179857636> 2224368 6 basuke 2026-06-26 17:40:22 -0700 Pull request: https://github.com/WebKit/WebKit/pull/67993 2226334 7 ews-feeder 2026-07-02 14:41:19 -0700 Committed 316426@main (7a422d312c3c): <https://commits.webkit.org/316426@main> Reviewed commits have been landed. Closing PR #67993 and removing active labels.