fix(solid): guard devComponent against undefined owner

[elcoosp]

Summary

devComponent (in packages/solid/src/client/core.ts) unconditionally dereferenced getOwner() and assigned owner._component, throwing "Cannot read properties of undefined (reading '[something]')" — surfacing as REACTIVITY_HALTED — whenever a component is rendered inside a root that has no enclosing owner.

This happens with a legally nested root: e.g. a component rendered inside a router's Provider/transparent root that is itself created within another owner. In dev builds this hard-crashes the entire reactive system. Production builds never hit this path.

Fix

The _component metadata is dev-only decoration. Guard it with if (owner) so it is skipped gracefully when there is no enclosing owner.

Reproduction

Render any component through a nested transparent root (createRoot(() => createRoot(() => <Comp/>, {transparent:true}), {transparent:true}), or a router Provider nested inside another root) in a dev build → devComponent throws. With the guard, it renders fine.

Scope

• Dev builds only (devComponent is dev instrumentation).
• No change to production behavior or public APIs.
• 1 file changed, +12 −5.

This was found while running vitest browser-mode tests against a Solid 2.0 app where a router Provider is nested inside a test render() root.