OOOS: rejecting deferred child under a Slot-projecting wrapper trips 'Missing child' assert on resume

What is it?

• Bug

Description

Under out-of-order streaming, when a Slot-projecting wrapper contains a sibling element and a <Suspense> whose deferred child rejects, the resumed client throws Internal assert ... Missing child at vnode_getChildWithIdx (core/client/vnode-utils.ts:873) via vnode_locate ← DomContainer.vNodeLocate ← ensureProjectionResolved ← materializeFromVNodeData ← vnode_materialize.

The rejection is required: an identical topology whose deferred child resolves late produces no assert and stays interactive. Reproduces at d54b5d436 (merge-base with main) — pre-existing, not caused by the ErrorBoundary branch where it was found.

Repro recipe

Router app served by the qwik-e2e dev-server; one route rendering: a Slot-projecting wrapper containing a sibling <div> and a <Suspense> whose child, on the server, returns waitForRelease(...).then(() => { throw new Error("boom") }) (release-gated so the shell streams first). POST the data-release-url, let the page resume, then click any signal-bumping button — the assert fires during materialization.

Two traps when bisecting against the merge-base from a feature branch: git checkout <merge-base> -- packages/qwik/src resurrects files the branch deleted (remove them manually or the build silently uses stale modules), and packages/qwik/handlers.mjs + packages/qwik/public.d.ts live outside src and must be reverted together.

Found migrating the error-handling e2e suite (#8745 stack); the affected e2e test is parked as test.fixme referencing this issue. Likely the same OOOS vnode-data family as #8876 but no shared-root evidence yet.

Start with the affected error-handling e2e test, currently parked as test.fixme, and reproduce it through the qwik-e2e dev-server with the release-gated rejecting Suspense child. Trace the reported path from core/client/vnode-utils.ts:873 through vnode_locate, DomContainer.vNodeLocate, ensureProjectionResolved, and materializeFromVNodeData. Done means the rejection case resumes without the Missing child assert and remains interactive.