2.0: Nested route layouts remount on every navigation between their children

[cradle-song]

Describe the bug

A shared parent layout is torn down and re-created on every navigation between its child routes, even though its route stays in the match chain and the router correctly reuses its route context. This contradicts the documented behavior:

Solid Router reuses a matched route context while its route definition remains in the next match chain. Moving between sibling child routes therefore keeps their shared parent layout mounted.

The bug affects any nested routes -- path-ful and pathless layouts alike. Only navigations that change no level of the match chain (same leaf route, different params) are unaffected.

Fallout: everything that lives in a layout is destroyed per click -- component state resets, onCleanup fires, providers are re-created, and CSS transitions never play.

Your Example Website or App

https://github.com/cradle-song/repro-solid-router-remount

Steps to Reproduce the Bug or Issue

1. Open the app (with the browser console visible)
2. Click Page A
3. Click Page B

Expected behavior

The page shows Layout instance #1. One Layout mount #1 console log at startup, new clicks do not log anything.

Screenshots or Videos

The page shows Layout instance #N. Every click logs new Layout mount #N

Platform

• Version: 2.0.0-next.17

Additional context

Suggested fix in repo README.