Refactor: unify invoice builder response paths (remove respond_with* split)

This refactor removes the separate `respond_with` / `respond_with_no_std`
variants and replaces them with a single unified
`respond_using_derived_keys(created_at)` API.

Reasoning:
- Upcoming recurrence logic requires setting `invoice_recurrence_basetime`
  based on the invoice’s `created_at` timestamp.
- For consistency with Offer and Refund builders, we want a single method
  that accepts an explicit `created_at` value at the callsite.
- The only real difference between the std/no_std response paths was how
  `created_at` was sourced; once it becomes a parameter, the split becomes
  unnecessary.

This change consolidates the response flow, reduces API surface, and
makes future recurrence-related changes simpler and more uniform across
Offer, InvoiceRequest, and Refund builders.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -13236,6 +13236,13 @@ where
 
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
 
+		#[cfg(not(feature = "std"))]
+		let created_at = Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64);
+		#[cfg(feature = "std")]
+		let created_at = std::time::SystemTime::now()
+			.duration_since(std::time::SystemTime::UNIX_EPOCH)
+			.expect("SystemTime::now() should come after SystemTime::UNIX_EPOCH");
+
 		let builder = self.flow.create_invoice_builder_from_refund(
 			&self.router,
 			entropy,
@@ -13245,6 +13252,7 @@ where
 				self.create_inbound_payment(Some(amount_msats), relative_expiry, None)
 					.map_err(|()| Bolt12SemanticError::InvalidAmount)
 			},
+			created_at
 		)?;
 
 		let invoice = builder.allow_mpp().build_and_sign(secp_ctx)?;
@@ -15407,6 +15415,13 @@ where
 					Err(_) => return None,
 				};
 
+				#[cfg(not(feature = "std"))]
+				let created_at = Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64);
+				#[cfg(feature = "std")]
+				let created_at = std::time::SystemTime::now()
+					.duration_since(std::time::SystemTime::UNIX_EPOCH)
+					.expect("SystemTime::now() should come after SystemTime::UNIX_EPOCH");
+
 				let get_payment_info = |amount_msats, relative_expiry| {
 					self.create_inbound_payment(
 						Some(amount_msats),
@@ -15422,6 +15437,7 @@ where
 							&request,
 							self.list_usable_channels(),
 							get_payment_info,
+							created_at
 						);
 
 						match result {
@@ -15446,6 +15462,7 @@ where
 							&request,
 							self.list_usable_channels(),
 							get_payment_info,
+							created_at
 						);
 
 						match result {

lightning/src/ln/offers_tests.rs

@@ -2337,7 +2337,7 @@ fn fails_paying_invoice_with_unknown_required_features() {
 
 	let invoice = match verified_invoice_request {
 		InvoiceRequestVerifiedFromOffer::DerivedKeys(request) => {
-			request.respond_using_derived_keys_no_std(payment_paths, payment_hash, created_at).unwrap()
+			request.respond_using_derived_keys(payment_paths, payment_hash, created_at).unwrap()
 				.features_unchecked(Bolt12InvoiceFeatures::unknown())
 				.build_and_sign(&secp_ctx).unwrap()
 		},

lightning/src/ln/outbound_payment.rs

@@ -3206,7 +3206,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), created_at).unwrap()
+			.respond_with(payment_paths(), payment_hash(), created_at).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 
@@ -3253,7 +3253,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
+			.respond_with(payment_paths(), payment_hash(), now()).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 
@@ -3316,7 +3316,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(&expanded_key, nonce, &secp_ctx, payment_id).unwrap()
 			.build_and_sign().unwrap()
-			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
+			.respond_with(payment_paths(), payment_hash(), now()).unwrap()
 			.build().unwrap()
 			.sign(recipient_sign).unwrap();
 

lightning/src/offers/flow.rs

@@ -932,7 +932,7 @@ where
 	/// This is not exported to bindings users as builder patterns don't map outside of move semantics.
 	pub fn create_invoice_builder_from_refund<'a, ES: Deref, R: Deref, F>(
 		&'a self, router: &R, entropy_source: ES, refund: &'a Refund,
-		usable_channels: Vec<ChannelDetails>, get_payment_info: F,
+		usable_channels: Vec<ChannelDetails>, get_payment_info: F, created_at: Duration,
 	) -> Result<InvoiceBuilder<'a, DerivedSigningPubkey>, Bolt12SemanticError>
 	where
 		ES::Target: EntropySource,
@@ -963,18 +963,7 @@ where
 			)
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
-		#[cfg(feature = "std")]
 		let builder = refund.respond_using_derived_keys(
-			payment_paths,
-			payment_hash,
-			expanded_key,
-			entropy,
-		)?;
-
-		#[cfg(not(feature = "std"))]
-		let created_at = Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64);
-		#[cfg(not(feature = "std"))]
-		let builder = refund.respond_using_derived_keys_no_std(
 			payment_paths,
 			payment_hash,
 			created_at,
@@ -1001,7 +990,7 @@ where
 	/// - The [`InvoiceBuilder`] could not be created from the [`InvoiceRequest`].
 	pub fn create_invoice_builder_from_invoice_request_with_keys<'a, R: Deref, F>(
 		&self, router: &R, invoice_request: &'a VerifiedInvoiceRequest<DerivedSigningPubkey>,
-		usable_channels: Vec<ChannelDetails>, get_payment_info: F,
+		usable_channels: Vec<ChannelDetails>, get_payment_info: F, created_at: Duration,
 	) -> Result<(InvoiceBuilder<'a, DerivedSigningPubkey>, MessageContext), Bolt12SemanticError>
 	where
 		R::Target: Router,
@@ -1030,15 +1019,8 @@ where
 			)
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
-		#[cfg(feature = "std")]
-		let builder = invoice_request.respond_using_derived_keys(payment_paths, payment_hash);
-		#[cfg(not(feature = "std"))]
-		let builder = invoice_request.respond_using_derived_keys_no_std(
-			payment_paths,
-			payment_hash,
-			Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64),
-		);
-		let builder = builder.map(|b| InvoiceBuilder::from(b).allow_mpp())?;
+		let builder = invoice_request.respond_using_derived_keys(payment_paths, payment_hash, created_at)
+			.map(|b| InvoiceBuilder::from(b).allow_mpp())?;
 
 		let context = MessageContext::Offers(OffersContext::InboundPayment { payment_hash });
 
@@ -1061,7 +1043,7 @@ where
 	/// - The [`InvoiceBuilder`] could not be created from the [`InvoiceRequest`].
 	pub fn create_invoice_builder_from_invoice_request_without_keys<'a, R: Deref, F>(
 		&self, router: &R, invoice_request: &'a VerifiedInvoiceRequest<ExplicitSigningPubkey>,
-		usable_channels: Vec<ChannelDetails>, get_payment_info: F,
+		usable_channels: Vec<ChannelDetails>, get_payment_info: F, created_at: Duration,
 	) -> Result<(InvoiceBuilder<'a, ExplicitSigningPubkey>, MessageContext), Bolt12SemanticError>
 	where
 		R::Target: Router,
@@ -1090,16 +1072,8 @@ where
 			)
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
-		#[cfg(feature = "std")]
-		let builder = invoice_request.respond_with(payment_paths, payment_hash);
-		#[cfg(not(feature = "std"))]
-		let builder = invoice_request.respond_with_no_std(
-			payment_paths,
-			payment_hash,
-			Duration::from_secs(self.highest_seen_timestamp.load(Ordering::Acquire) as u64),
-		);
-
-		let builder = builder.map(|b| InvoiceBuilder::from(b).allow_mpp())?;
+		let builder = invoice_request.respond_with(payment_paths, payment_hash, created_at)
+			.map(|b| InvoiceBuilder::from(b).allow_mpp())?;
 
 		let context = MessageContext::Offers(OffersContext::InboundPayment { payment_hash });