Warn when mounting different apps on the same host element

Editor assessment

The subject is clear and actionable — 'warn when mounting different apps on the same host element' names the trigger and the new behavior — and imperative, lowercase, with a (#5573) reference. My quibble is the type: introducing a new developer-facing warning is arguably feat, since changelog consumers may want it highlighted, whereas chore signals invisible maintenance; fix is defensible only if a warning regression is involved. The missing scope (runtime-core, presumably) also weakens filtering in a codebase that otherwise scopes consistently. No body, but the behavior described is self-explanatory. Solid, with type choice the main debate.