Deterministic reconstruct_manager option in tests

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index e50a9b8..569bb37 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -17819,6 +17819,15 @@ pub struct ChannelManagerReadArgs<
 	///
 	/// This is not exported to bindings users because we have no HashMap bindings
 	pub channel_monitors: HashMap<ChannelId, &'a ChannelMonitor<SP::EcdsaSigner>>,
+
+	/// Whether the `ChannelManager` should attempt to reconstruct its set of pending HTLCs from
+	/// `Channel{Monitor}` data rather than its own persisted maps, which is planned to become
+	/// the default behavior in upcoming versions.
+	///
+	/// If `None`, whether we reconstruct or use the legacy maps will be decided randomly during
+	/// `ChannelManager::from_channel_manager_data`.
+	#[cfg(test)]
+	pub reconstruct_manager_from_monitors: Option<bool>,
 }
 
 impl<
@@ -17856,6 +17865,8 @@ impl<
 			channel_monitors: hash_map_from_iter(
 				channel_monitors.drain(..).map(|monitor| (monitor.channel_id(), monitor)),
 			),
+			#[cfg(test)]
+			reconstruct_manager_from_monitors: None,
 		}
 	}
 }
@@ -18553,26 +18564,30 @@ impl<
 		#[cfg(not(test))]
 		let reconstruct_manager_from_monitors = false;
 		#[cfg(test)]
-		let reconstruct_manager_from_monitors = {
-			use core::hash::{BuildHasher, Hasher};
-
-			match std::env::var("LDK_TEST_REBUILD_MGR_FROM_MONITORS") {
-				Ok(val) => match val.as_str() {
-					"1" => true,
-					"0" => false,
-					_ => panic!("LDK_TEST_REBUILD_MGR_FROM_MONITORS must be 0 or 1, got: {}", val),
-				},
-				Err(_) => {
-					let rand_val =
-						std::collections::hash_map::RandomState::new().build_hasher().finish();
-					if rand_val % 2 == 0 {
-						true
-					} else {
-						false
-					}
-				},
-			}
-		};
+		let reconstruct_manager_from_monitors =
+			args.reconstruct_manager_from_monitors.unwrap_or_else(|| {
+				use core::hash::{BuildHasher, Hasher};
+
+				match std::env::var("LDK_TEST_REBUILD_MGR_FROM_MONITORS") {
+					Ok(val) => match val.as_str() {
+						"1" => true,
+						"0" => false,
+						_ => panic!(
+							"LDK_TEST_REBUILD_MGR_FROM_MONITORS must be 0 or 1, got: {}",
+							val
+						),
+					},
+					Err(_) => {
+						let rand_val =
+							std::collections::hash_map::RandomState::new().build_hasher().finish();
+						if rand_val % 2 == 0 {
+							true
+						} else {
+							false
+						}
+					},
+				}
+			});
 
 		// If there's any preimages for forwarded HTLCs hanging around in ChannelMonitors we
 		// should ensure we try them again on the inbound edge. We put them here and do so after we
diff --git a/lightning/src/ln/functional_test_utils.rs b/lightning/src/ln/functional_test_utils.rs
index 6800078..25b5408 100644
--- a/lightning/src/ln/functional_test_utils.rs
+++ b/lightning/src/ln/functional_test_utils.rs
@@ -911,6 +911,8 @@ impl<'a, 'b, 'c> Drop for Node<'a, 'b, 'c> {
 						tx_broadcaster: &broadcaster,
 						logger: &self.logger,
 						channel_monitors,
+						#[cfg(test)]
+						reconstruct_manager_from_monitors: None,
 					},
 				)
 				.unwrap();
@@ -1309,7 +1311,7 @@ fn check_claimed_htlcs_match_route<'a, 'b, 'c>(
 
 pub fn _reload_node<'a, 'b, 'c>(
 	node: &'a Node<'a, 'b, 'c>, config: UserConfig, chanman_encoded: &[u8],
-	monitors_encoded: &[&[u8]],
+	monitors_encoded: &[&[u8]], _reconstruct_manager_from_monitors: Option<bool>,
 ) -> TestChannelManager<'b, 'c> {
 	let mut monitors_read = Vec::with_capacity(monitors_encoded.len());
 	for encoded in monitors_encoded {
@@ -1343,6 +1345,8 @@ pub fn _reload_node<'a, 'b, 'c>(
 				tx_broadcaster: node.tx_broadcaster,
 				logger: node.logger,
 				channel_monitors,
+				#[cfg(test)]
+				reconstruct_manager_from_monitors: _reconstruct_manager_from_monitors,
 			},
 		)
 		.unwrap()
@@ -1378,7 +1382,7 @@ macro_rules! reload_node {
 		$node.chain_monitor = &$new_chain_monitor;
 
 		$new_channelmanager =
-			_reload_node(&$node, $new_config, &chanman_encoded, $monitors_encoded);
+			_reload_node(&$node, $new_config, &chanman_encoded, $monitors_encoded, None);
 		$node.node = &$new_channelmanager;
 		$node.onion_messenger.set_offers_handler(&$new_channelmanager);
 		$node.onion_messenger.set_async_payments_handler(&$new_channelmanager);
diff --git a/lightning/src/ln/reload_tests.rs b/lightning/src/ln/reload_tests.rs
index 360ffe2..cac1871 100644
--- a/lightning/src/ln/reload_tests.rs
+++ b/lightning/src/ln/reload_tests.rs
@@ -438,6 +438,7 @@ fn test_manager_serialize_deserialize_inconsistent_monitor() {
 		tx_broadcaster: nodes[0].tx_broadcaster,
 		logger: &logger,
 		channel_monitors: node_0_stale_monitors.iter().map(|monitor| { (monitor.channel_id(), monitor) }).collect(),
+		reconstruct_manager_from_monitors: None,
 	}) { } else {
 		panic!("If the monitor(s) are stale, this indicates a bug and we should get an Err return");
 	};
@@ -456,6 +457,7 @@ fn test_manager_serialize_deserialize_inconsistent_monitor() {
 		tx_broadcaster: nodes[0].tx_broadcaster,
 		logger: &logger,
 		channel_monitors: node_0_monitors.iter().map(|monitor| { (monitor.channel_id(), monitor) }).collect(),
+		reconstruct_manager_from_monitors: None,
 	}).unwrap();
 	nodes_0_deserialized = nodes_0_deserialized_tmp;
 	assert!(nodes_0_read.is_empty());