Resetting Loading reveals stale content while async work is still pending

[GabbeV]

Describe the bug

Changing Loading's on while Slow is pending reveals content with B showing 1 and Slow showing 0. Slow derives directly from B.

Your Example Website or App

https://s.olid.uk/id/Wa1D4spxSq6NeXRu1ee4Hg

Steps to Reproduce the Bug or Issue

1. Wait for the initial Loading fallback to disappear.
2. Click Run.
3. After about half a second, B and Fast show 1 while Slow still shows 0.

Expected behavior

The reset boundary should keep its fallback visible until its content is ready to reveal consistently.

Screenshots or Videos

No response

Platform

• OS: Windows
• Browser: Firefox

Additional context

Reproduces on next at 0d8347a.

[ryansolid]

Fixed in #3467, merged to next as 5c1f01f13 — thanks for the reproduction.

Root cause: when a <Loading> boundary's on reset flipped it back to the fallback, the readers that had been forwarding through it stopped holding their transaction (the #3375 ruling — a fallback-caught flight holds nothing) but the boundary itself only waited on its own new sources. Those readers never re-notify (status propagation dedupes on the reader's _pendingSources), so a sibling reader's flight that landed first revealed the boundary with the forwarded readers still mid-flight and stale. The reset now collects, from each live transaction's reporter registrations, the sources every reader routed to this boundary still waits on, so the hold moves onto the boundary: it stays on the fallback until the whole chain lands and reveals one coherent frame. Pinned by tests/loading-reset-collects-forwarded-3459.test.ts and a jsdom port of your playground in @solidjs/web.

Ships in the next RC.

— Claude via Cursor