Persist splice intents until the splice locks

LDK only persists a splice once its negotiation reaches
AwaitingSignatures, so a splice in flight when the node stops can leave
no trace in LDK. Persist each user-initiated splice as an intent record
before its contribution is handed to LDK, so such a splice can be
recognized at the next startup — releasing whatever the wallet still
holds for it, which a later commit adds — and so events about the
splice can be described in terms of the original request.

A fee bump reuses the channel's existing intent record, so at most one
record ever exists per channel. The record is undone when LDK rejects
the hand-off synchronously and settled once the splice locks, its
failure is surfaced, or its channel closes. A failure event settles the
intent only after the event is durably queued — a crash in between
leaves the intent for the replayed event to settle, erring toward a
duplicate report over a lost one — and only when the event's
contribution identifies the recorded splice: a mismatch means the
failure concerns an older, superseded attempt with no record of its
own. A splice queued behind another pending splice survives the pending
splice's lock, so its intent is re-anchored to the new funding rather
than settled.

Wallet state staged on a splice's behalf is flushed only after the
intent record persists, so nothing the wallet reserves for a splice can
outlive the record through which a later startup would release it. A
splice that fails before the hand-off releases what the wallet holds
for it immediately; one LDK rejects has it returned through the
DiscardFunding event instead. When a lock settles an intent without
spending its inputs — a replacement or counterparty-initiated splice
locked instead — the inputs are released for other spends.

Once a splice funding payment is classified, the intent is carried on
the payment's record until the splice locks; a payment that already
graduated instead removes the leftover intent record.

Developed with assistance from Claude Code.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: jkczyz

src/builder.rs

@@ -53,6 +53,7 @@ use lightning_dns_resolver::OMDomainResolver;
 use vss_client::headers::VssHeaderProvider;
 
 use crate::chain::ChainSource;
+use crate::channel::SpliceTracker;
 #[cfg(feature = "chain-bitcoind")]
 use crate::config::BitcoindRestClientConfig;
 use crate::config::{
@@ -2451,6 +2452,14 @@ fn build_with_store_internal(
 		})
 	});
 
+	let splice_tracker = Arc::new(SpliceTracker::new(
+		Arc::clone(&channel_manager),
+		Arc::clone(&wallet),
+		Arc::clone(&pending_payment_store),
+		Arc::clone(&payment_store),
+		Arc::clone(&logger),
+	));
+
 	#[cfg(cycle_tests)]
 	let mut _leak_checker = crate::LeakChecker(Vec::new());
 	#[cfg(cycle_tests)]
@@ -2490,6 +2499,7 @@ fn build_with_store_internal(
 		scorer,
 		peer_store,
 		payment_store,
+		splice_tracker,
 		lnurl_auth,
 		is_running,
 		node_metrics,