Error reporting in a context

Important: start the server with CK_DEBUG=false pnpm manual, for the same reason as in the other error reporting test.

Two editors share one Context, and the context has a context plugin of its own. A single onEditorError() callback logs every reported error together with what it was attributed to. Keep the console open — nothing is swallowed.

1. Click Throw from an editor plugin under the first editor. One entry naming editor 1. Then do the same under the second editor: one entry naming editor 2. Sharing a context must not make them look alike.
2. Click Throw from the context itself. The error is thrown with the Context as its context, so the entry should name the context. This is the case where the reported source is not an editor at all.
3. Click Throw from a context plugin. The plugin is shared by both editors, so no single editor owns the error and the entry should name the context, just like case 2.
4. Type in both editors, then throw again from either. Nothing restarts, so both editors keep their content and their undo history.

How the source is decided. Editors are asked first, one at a time, and only what none of them claims is offered to the context. An error is the context's own exactly when no editor in it has already taken responsibility.