[unstable2507] Backport #10311: [Staking] Async Election and Export

cumulus/parachains/runtimes/assets/asset-hub-westend/src/staking.rs

@@ -294,7 +294,7 @@ impl pallet_staking_async::Config for Runtime {
 	type EventListeners = (NominationPools, DelegatedStaking);
 	type WeightInfo = weights::pallet_staking_async::WeightInfo<Runtime>;
 	type MaxInvulnerables = frame_support::traits::ConstU32<20>;
-	type PlanningEraOffset = PlanningEraOffset;
+	type PlanningEraOffset = ConstU32<6>;
 	type RcClientInterface = StakingRcClient;
 	type MaxEraDuration = MaxEraDuration;
 	type MaxPruningItems = MaxPruningItems;
@@ -305,6 +305,8 @@ impl pallet_staking_async_rc_client::Config for Runtime {
 	type AHStakingInterface = Staking;
 	type SendToRelayChain = StakingXcmToRelayChain;
 	type MaxValidatorSetRetries = ConstU32<64>;
+	// export validator session at end of session 4 within an era.
+	type ValidatorSetExportSession = ConstU32<4>;
 }
 
 #[derive(Encode, Decode)]

prdoc/pr_10311.prdoc

@@ -0,0 +1,20 @@
+title: '[Staking] Async Elections Post AHM'
+doc:
+- audience: Runtime Dev
+  description: |-
+    Staking elections can be configured so they run as soon as the era starts, but their results are buffered and
+    only sent to RC after the end of session `n - 2` and before start of session `n - 1`, assuming the new validator set
+    must activate at end of session `n`.
+
+    This helps us avoid difficulty of timing the election precisely as elections are long running and can sometimes
+    take longer than usual.
+
+    See documentation for `pallet_staking_async::Config::PlanningEraOffset` and
+    `pallet_staking_async_rc_client::Config::ValidatorSetExportSession` to learn more.
+crates:
+- name: pallet-staking-async
+  bump: minor
+- name: pallet-staking-async-rc-client
+  bump: minor
+- name: asset-hub-westend-runtime
+  bump: minor