Isolate identity changes and persisted cache ownership

Parent

An existing browser owner/tenant switch cannot leak private cache data or be repopulated by old work.

Capture the old owner, cancel its queries/streams, handle pending mutations deliberately, clear private cached/persisted state, and construct the new owner's utilities.
Prove late old-owner mutation callbacks cannot seed or invalidate new-owner private entries.
Use safe result-changing identity/session/permission generations and never bearer credentials as keys.
Demonstrate identity-scoped persistence and schema/version busters with rejection of incompatible restored data.
Use existing application scenarios and minimal copied consumers; add no new authentication/session manager, showcase application, or example dependency.