Nursery: Don't pass exceptions to main loop

README.md

@@ -190,11 +190,10 @@ nursery.openAdmission();
 
 auto lease = nursery.getNewSlotLease();
 lease.getSyncCanceler().startAcceptingWork();
-std::exception_ptr &exceptionStorage = lease.getExceptionStorage();
 lease.setOnSettledHook(
-	[&exceptionStorage]()
+	[](std::exception_ptr &exceptionPtr)
 	{
-		sscl::co::NonViralCompletion nvc(exceptionStorage);
+		sscl::co::NonViralCompletion nvc(exceptionPtr);
 		nvc.checkAndRethrowException();
 	});
 lease.fillSlot(
@@ -221,10 +220,9 @@ all slots have retired naturally and throw if admission is still open.
 `Slot::Lease` is commit-required: an uncommitted lease removes its reservation on
 destruction. `fillSlot()` takes an invoker factory (deferred construction) because
 non-viral coroutines may complete synchronously during invoker construction.
-The factory may capture `lease` by reference; `setOnSettledHook()` may not.
-The hook runs after the lease is destroyed, so capture slot-owned state such as
-`lease.getExceptionStorage()` (a reference to the slot's `exceptionPtr`), not
-`lease` itself.
+The factory may capture `lease` by reference; `setOnSettledHook()` may not
+capture `lease` itself. The nursery passes the slot's `exceptionPtr` into the
+hook at retirement.
 `Slot::Handle` is an opaque slot pointer valid only while the slot remains in the
 nursery.