[2.0 / next] A direct write does not clear a writable memo's previous error #4110

Describe the bug

A writable memo throws during its initial derivation, and <Errored> shows the error. A button outside the boundary calls its setter with 2, but the boundary continues showing the original error instead of rendering the written value.

Your Example Website or App

https://s.olid.uk/id/PmShIVyvSYWMQLTS5qkkSA

Steps to Reproduce the Bug or Issue

1. Open the playground. The boundary shows Error: boom.
2. Click Set value to 2.
3. The boundary continues showing Error: boom instead of Value: 2.

Expected behavior

The direct write should replace the memo's failed outcome with 2, allowing the boundary to recover and render Value: 2 without rerunning the derivation.

Screenshots or Videos

No response

Platform

• OS: Linux
• Browser: Chromium 154.0.8037.57
• Solid: playground pinned to next@d5e32a9af41c7bfe0bc090f7438ee4297d540b17. A reduced source regression also fails on current next@ccd99481deed3ebb567ee11ab7a152ced84d122b.

Additional context

The createSignal documentation says a direct write lands without rerunning the derivation.

The failure also affects ordinary accessor reads and createEffect, which retain the old error after a write. This playground makes it visible through an error boundary.

The failed-writable-memo cases from #3886 are explicitly outside #4085's held-error rule. #3886 contains related regression tests and candidate changes.