[🐞] ErrorBoundary: late-delivered fallback leaves the errored content's serialized state live

Which component is affected?

Qwik Runtime

Describe the bug

When a boundary sits outside a <Suspense> whose child rejects after the root has streamed (out-of-order, the default under the suspense flag), the fallback is delivered late through $emitFallback$. The rethrow-into-segment exit skips markErrorBoundaryContentInert, and by that point the root has already emitted its state and vnode-data — so the inert cut cannot reach the wire. The errored content resumes with live effect subscriptions: a bound attribute inside the hidden content keeps tracking, and a signal write updates the dead DOM (a bound img src fires a real network request for a torn-down subtree).

The DOM half is handled (the late path now registers a qErr swap that hides the content host and strips its q-d:*/q-w:* handlers). The state half needs a way to retract already-emitted rows, which the vnode-data patch channel cannot express today: patches only add or replace rows that carry data; an INERT-gated row emits as separator-only and leaves the earlier live row standing.

Reproduction

Pinned (skipped) in packages/qwik/src/core/tests/error-boundary.spec.tsx, describe "ErrorBoundary late-delivered fallback": "marks the errored content inert: a bound attribute stops tracking after resume".

System Info

Qwik v2, build/v2 lineage (PR #8745 branch), experimental errorBoundary + suspense flags

Additional Information

Same family as the retained-element-effects residue: the in-order path clears effects before emission; the late path has no emission left to gate.

Start with the skipped reproduction in packages/qwik/src/core/tests/error-boundary.spec.tsx, under “ErrorBoundary late-delivered fallback.” Trace the late $emitFallback$ path, markErrorBoundaryContentInert, and the vnode-data patch channel. Done means the resumed errored content is inert: its bound attribute no longer tracks or updates the dead DOM after the fallback arrives.