[plumb] Add forced async invoice refresh selection

Async receive offers currently decide static invoice refreshes from
timer-based freshness only. Channel changes need a separate selector so
callers can rebuild server-side invoices without waiting for the normal age
threshold.

Add a cache helper that returns used and pending offers for forced invoice
refresh. Ready offers stay on the existing offer rotation path because they
have not been returned to the application yet.

AI-assisted: planning and writing commit

Co-Authored-By: OpenAI Codex <codex@openai.com>

Author: shaavan

lightning/src/offers/async_receive_offer_cache.rs

@@ -469,6 +469,32 @@ impl AsyncReceiveOfferCache {
 		})
 	}
 
+	/// Returns cached offers whose static invoices should be refreshed after a local channel change.
+	pub(super) fn offers_needing_forced_invoice_refresh(
+		&self,
+	) -> impl Iterator<Item = (&Offer, Nonce, &Responder)> {
+		self.offers_with_idx().filter_map(move |(_, offer)| {
+			let needs_invoice_update = match offer.status {
+				// Used offers may already be published by the application. Keep their server-side
+				// invoices aligned with our current channels instead of waiting for the timer
+				// threshold.
+				OfferStatus::Used { .. } => true,
+				// Pending offers have already been sent to the server, but are not confirmed yet.
+				// Re-sending them is safe and matches the normal timer retry behavior.
+				OfferStatus::Pending => true,
+				// Ready offers have not been handed to the application yet. They are rotated by the
+				// offer-refresh path, so forcing invoice updates for them would mostly create extra
+				// server churn without helping published offers.
+				OfferStatus::Ready { .. } => false,
+			};
+			if needs_invoice_update {
+				Some((&offer.offer, offer.offer_nonce, &offer.update_static_invoice_path))
+			} else {
+				None
+			}
+		})
+	}
+
 	/// Should be called when we receive a [`StaticInvoicePersisted`] message from the static invoice
 	/// server, which indicates that a new offer was persisted by the server and they are ready to
 	/// serve the corresponding static invoice to payers on our behalf.