Dart transfer tokens cannot report the loss of every alias

[sargunv]

Tracked from the Dart binding review log on the dart branch (#187).

ResourceRequestToken is isolate-sendable and may have independent copies. The native registry releases it on explicit completion or close, but cannot identify when every Dart copy has been lost. A finalizer on one copy could terminate a request still owned by another isolate, and making the token Finalizable would make it unsendable — Dart refuses to send Finalizable instances across isolate boundaries.

The same tension produced a second, narrower gap tracked separately: WakeSource drops leak reporting entirely to stay transferable.

Suggested next step: design registry-backed alias leases, or an explicit transfer protocol with deterministic last-owner reporting.

Area: owned-handle leak reporting. Severity: medium. Complexity: high.

[sargunv-bot]

Closing as not planned because #433 removes cross-isolate transfer of resource-request handles from the binding contract. The receiver that drains an adapter record owns and completes its request handle. Other execution contexts may receive copied request data and return copied response data. We can reconsider explicit ownership transfer if a concrete integration requires the handle itself to move between isolates or realms.