Introduce recurrence state-update logic

This commit adds the final piece of the payee-side recurrence flow:
updating the internal `next_payable_counter` once a recurring payment
has been successfully claimed.

The update is performed immediately before emitting the
`PaymentClaimed` event, ensuring the counter is advanced only after the
payment is fully completed and acknowledged by the node. This provides a
clear correctness boundary and avoids premature state transitions.

The approach is intentionally conservative for this PoC. Future
refinements may place the update earlier in the pipeline or integrate it
more tightly with the payment-claim flow, but the current design offers
simple and reliable semantics.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -50,7 +50,7 @@ use crate::chain::transaction::{OutPoint, TransactionData};
 use crate::chain::{BestBlock, ChannelMonitorUpdateStatus, Confirm, Watch};
 use crate::events::{
 	self, ClosureReason, Event, EventHandler, EventsProvider, HTLCHandlingFailureType,
-	InboundChannelFunds, PaymentFailureReason, ReplayEvent,
+	InboundChannelFunds, PaymentFailureReason, PaymentPurpose, ReplayEvent,
 };
 use crate::events::{FundingInfo, PaidBolt12Invoice};
 use crate::ln::chan_utils::selected_commitment_sat_per_1000_weight;
@@ -93,7 +93,9 @@ use crate::offers::async_receive_offer_cache::AsyncReceiveOfferCache;
 use crate::offers::flow::{HeldHtlcReplyPath, InvreqResponseInstructions, OffersMessageFlow};
 use crate::offers::invoice::{Bolt12Invoice, UnsignedBolt12Invoice};
 use crate::offers::invoice_error::InvoiceError;
-use crate::offers::invoice_request::{InvoiceRequest, InvoiceRequestVerifiedFromOffer};
+use crate::offers::invoice_request::{
+	InvoiceRequest, InvoiceRequestFields, InvoiceRequestVerifiedFromOffer,
+};
 use crate::offers::nonce::Nonce;
 use crate::offers::offer::{Offer, OfferFromHrn, RecurrenceData, RecurrenceFields};
 use crate::offers::parse::Bolt12SemanticError;
@@ -9514,6 +9516,32 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 						payment_id,
 						durable_preimage_channel,
 					}) = payment {
+						// At this point, the payment has been successfully claimed. If it belongs
+						// to a recurring offer, we can safely advance the recurrence state.
+
+						match &purpose {
+							PaymentPurpose::Bolt12OfferPayment {
+								payment_context: Bolt12OfferContext {
+									invoice_request: InvoiceRequestFields {
+										payer_signing_pubkey,
+										recurrence_counter: Some(paid_counter),
+										..
+									},
+									..
+								},
+								..
+							} => {
+								let mut sessions = self.active_recurrence_sessions.lock().unwrap();
+
+								if let Some(data) = sessions.get_mut(payer_signing_pubkey) {
+									if data.next_payable_counter == *paid_counter {
+										data.next_payable_counter += 1;
+									}
+								}
+							},
+							_ => {}
+						}
+
 						let event = events::Event::PaymentClaimed {
 							payment_hash,
 							purpose,