[2.0 / next] Outside latest reads of a derivation expose errors and values at different times #4106

Describe the bug

With derived = createMemo(() => latest(source)), outside reads of latest(derived) expose successful and failed outcomes at different points during a held update.

A successful result becomes readable before the frame reveals. A rejection only becomes observable through the derivation after reveal, even though direct latest(source) already throws it. An async sibling keeps the frame held in both cases.

Your Example Website or App

https://s.olid.uk/id/Bp_ILv8vREiTHbnn0x6Ppg

Steps to Reproduce the Bug or Issue

Wait for Derived effect: 1 and Committed round: 1. The Read latest button samples both accessors from an event handler, outside a reactive computation.

Rejected result:

1. Click Start update, then Reject source.
2. Click Read latest. The output shows latest(source): boom but latest(derived): 1. The read helper catches thrown errors and displays their messages. The committed round remains 1 because the sibling is still pending.
3. Click Release sibling, then Read latest again. Both reads now throw boom, and the committed round is 2.

Successful result:

1. Reload the playground.
2. Click Start update, then Resolve source to 2 (control).
3. Click Read latest before releasing the sibling. Both reads already return 2, while the committed round remains 1.

Expected behavior

Outside reads should follow a consistent publication rule for successful and failed outcomes.

The point at which latest(derived) exposes a new outcome should not depend on whether the source fulfills or rejects.

Screenshots or Videos

No response

Platform

• OS: Linux
• Browser: Chromium 154.0.8037.57
• Solid: playground pinned to the next build at d5e32a9af41c7bfe0bc090f7438ee4297d540b17, which includes fix(signals): a held error waits for its frame (D-41) #4085.

Additional context

Related to #4085. Both the rejection and fulfillment paths were verified in the hosted playground.

The related publication rules are D-22 and D-41.