feat: restore aggregate at source

src/agreement/proposal.rs

@@ -65,7 +65,6 @@ pub(crate) enum Proposal {
 
     // Proposal to accumulate the message at the source (that is, our section) and then send it to
     // its destination.
-    // TODO: it seems we might not need this. Consider removing it.
     AccumulateAtSrc {
         message: Box<PlainMessage>,
         proof_chain: SectionChain,

src/routing/core.rs

@@ -2185,6 +2185,9 @@ impl Core {
                 proof_chain,
                 None,
             )?
+        } else if itinerary.aggregate_at_src() {
+            let proposal = self.create_aggregate_at_src_proposal(itinerary.dst, variant, None)?;
+            return self.propose(proposal);
         } else {
             Message::single_src(&self.node, itinerary.dst, variant, None, None)?
         };
@@ -2206,6 +2209,37 @@ impl Core {
         Ok(commands)
     }
 
+    fn create_aggregate_at_src_proposal(
+        &self,
+        dst: DstLocation,
+        variant: Variant,
+        proof_chain_first_key: Option<&bls::PublicKey>,
+    ) -> Result<Proposal> {
+        let proof_chain = self.create_proof_chain(&dst, proof_chain_first_key)?;
+        let dst_key = if let Some(name) = dst.name() {
+            *self.section_key_by_name(&name)
+        } else {
+            // NOTE: `dst` is `Direct`. We use this when we want the message to accumulate at the
+            // destination and also be handled only there. We only do this if the recipient is in
+            // our section, so it's OK to use our latest key as the `dst_key`.
+            *self.section.chain().last_key()
+        };
+
+        let message = PlainMessage {
+            src: self.section.prefix().name(),
+            dst,
+            dst_key,
+            variant,
+        };
+
+        let proposal = Proposal::AccumulateAtSrc {
+            message: Box::new(message),
+            proof_chain,
+        };
+        trace!("Created aggregate at source proposal {:?}", proposal);
+        Ok(proposal)
+    }
+
     fn send_message_for_dst_accumulation(
         &self,
         src: XorName,