Conditional JSX stays stale during a held branch change

[GabbeV]

Describe the bug

While an async memo holds show at true, updating count displays Count: 1 but leaves show() ? count() : "hidden" displaying 0.

Your Example Website or App

https://s.olid.uk/id/LTuZMI4_S8SJuZxMpv8QSQ

Steps to Reproduce the Bug or Issue

1. Wait for initialization.
2. Click Run.
3. After 500ms, Count becomes 1 while Show remains true and Panel remains 0.
4. After another 500ms, Show becomes false and Panel becomes hidden.

Expected behavior

Panel should agree with Count while Show is true.

Screenshots or Videos

No response

Platform

Verified with compiled JSX in jsdom on Node.js 24.18.0, in development and production builds.

Additional context

Reproduced on next at efcaeba, after #3431 merged, and on #3337 at 20f3143.

Related to #3410, but this is an inline JSX conditional. Wrapping the conditional in createMemo avoids the mismatch on next.

Unlike #3412, this needs no Loading boundary or reset; Show still correctly displays true during the mismatch.

[ryansolid]

Fixed in a0d6dd2 (#3439 by @brenelz), merged to next — ships in the next rc.

The compiler emits {show() ? count() : "hidden"} as an insert effect (only !!show() is memoized), and the #3431 rule that a staged pass keeps its dependency tail until the frame is replaced keyed on a memo's staged value slot, which an effect doesn't have — its frame is the run it owes, and that run was stashed when the same flush became a hold. The effect's pass dropped count at once, so setCount(1) never reached the frame still showing 0. Now an effect's dependencies are the committed frame's until its run applies: the count write reaches it and, as a mainline reader of the foreign hold, it re-derives Panel: 1 beside Count: 1; the landing reveals hidden with Show: false.

The memo-wrapped conditional keeps its shape (the count write joins the hold and reveals at the landing) — both frames are coherent; effects render mainline by design.

— Claude via Cursor