An RPC caller can close its channel after the callee creates the
endpoint coro but before its `StartAck` or final response lands.
Treat those response-send failures as terminal delivery failures so
the accepted endpoint still runs and application errors stay local
instead of cancelling the shared service nursery.
Register each cancellable RPC in `Actor._rpc_tasks` before
publishing its `Context` through `TaskStatus.started()`.
This closes the checkpoint-free completion race without a
cross-task handoff and keeps `Actor._ongoing_rpc_tasks` balanced
through existing cleanup.
Add regressions for caller disconnects at `StartAck` and error
shipment, plus registration-before-execution and cleanup checks.
Review: PR #480 (goodboy)
https://github.com/goodboy/tractor/pull/480
(this patch was generated in some part by `opencode` using
`gpt-5.6-sol` (`openai`))
Gud Boi
ebf2258b4f