fix: improve acknowledged unicast retry reliability (#11320)

* Improve acknowledged unicast retry reliability

* Fix merged next-hop routing tests

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/NextHopRouter.h

@@ -39,6 +39,9 @@ struct PendingPacket {
     /** Starts at NUM_RETRANSMISSIONS -1 and counts down.  Once zero it will be removed from the list */
     uint8_t numRetransmissions = 0;
 
+    /** Initial remaining retry count, used to detect whether a retry has fired. */
+    uint8_t initialNumRetransmissions = 0;
+
     PendingPacket() {}
     explicit PendingPacket(meshtastic_MeshPacket *p, uint8_t numRetransmissions);
 };
@@ -77,8 +80,8 @@ class GlobalPacketIdHashFunction
   Namely, in the PacketHistory, we keep track of (up to 3) relayers of a packet. When the ACK is delivered back to us via a node
   that also relayed the original packet, we use that node as next hop for the destination from then on. This makes sure that only
   when there’s a two-way connection, we assign a next hop. Both the ReliableRouter and NextHopRouter will do retransmissions (the
-  NextHopRouter only 1 time). For the final retry, if no one actually relayed the packet, it will reset the next hop in order to
-  fall back to the FloodingRouter again. Note that thus also intermediate hops will do a single retransmission if the intended
+  NextHopRouter only a small number of times). For the final retry, if no one actually relayed the packet, it will reset the next
+  hop in order to fall back to the FloodingRouter again. Intermediate hops also do bounded retransmissions if the intended
   next-hop didn’t relay, in order to fix changes in the middle of the route.
 */
 class NextHopRouter : public FloodingRouter
@@ -109,10 +112,12 @@ class NextHopRouter : public FloodingRouter
         return min(d, r);
     }
 
-    // The number of retransmissions intermediate nodes will do (actually 1 less than this)
-    constexpr static uint8_t NUM_INTERMEDIATE_RETX = 2;
-    // The number of retransmissions the original sender will do
+    // Total attempts for directed hop-level delivery, including the initial send.
+    constexpr static uint8_t NUM_INTERMEDIATE_RETX = 3;
+    // Existing reliable broadcast budget, including the initial send.
     constexpr static uint8_t NUM_RELIABLE_RETX = 3;
+    // Total attempts for acknowledged unicast from the originating node.
+    constexpr static uint8_t NUM_RELIABLE_UNICAST_ATTEMPTS = 5;
 
     // M3: bounded RAM route-health table (reuse-oldest eviction, like PacketHistory)
     constexpr static uint8_t ROUTE_HEALTH_MAX = 32;              // ~12B/slot -> ~384B
@@ -155,6 +160,8 @@ class NextHopRouter : public FloodingRouter
      */
     PendingPacket *startRetransmission(meshtastic_MeshPacket *p, uint8_t numReTx = NUM_INTERMEDIATE_RETX);
 
+    ErrorCode sendWithNextHop(meshtastic_MeshPacket *p, bool trackRetransmission);
+
     // Return true if we're allowed to cancel a packet in the txQueue (so we may never transmit it even once)
     bool roleAllowsCancelingFromTxQueue(const meshtastic_MeshPacket *p);