Consolidate extension runtime ownership behind the V2 lifecycle

[adhamhaithameid]

Summary

Reduce overlapping legacy ownership by moving more runtime behavior behind the shared V2 lifecycle without changing the user-facing experience.

Why

The extension works well now, but maintenance cost is still higher than it should be because old and new ownership paths overlap.

Scope

• identify the remaining legacy-owned hot paths
• reduce duplicate observers and lifecycle owners
• keep legacy available as rollback, not as the main place where new behavior grows
• preserve the current stable UX throughout the migration

Effect

Cleaner internals, better performance on heavy pages, and safer future engine work.