feat(shamap): inject Family PRNG into missing-node walks

NodeFamily forwards Application::getPrng. SHAMapSync draws first-child
offsets from that engine. TestNodeFamily keeps default_prng.

src/test/shamap/common.h

@@ -24,6 +24,7 @@
 #include <xrpld/nodestore/Manager.h>
 #include <xrpld/shamap/Family.h>
 #include <xrpl/basics/chrono.h>
+#include <xrpl/basics/random.h>
 
 namespace ripple {
 namespace tests {
@@ -80,6 +81,12 @@ public:
         return j_;
     }
 
+    beast::xor_shift_engine&
+    prng() override
+    {
+        return default_prng();
+    }
+
     std::shared_ptr<FullBelowCache>
     getFullBelowCache() override
     {

src/xrpld/shamap/Family.h

@@ -25,6 +25,7 @@
 #include <xrpld/shamap/TreeNodeCache.h>
 #include <xrpl/basics/Log.h>
 #include <xrpl/beast/utility/Journal.h>
+#include <xrpl/beast/xor_shift_engine.h>
 #include <cstdint>
 
 namespace ripple {
@@ -53,6 +54,9 @@ public:
     virtual beast::Journal const&
     journal() = 0;
 
+    virtual beast::xor_shift_engine&
+    prng() = 0;
+
     /** Return a pointer to the Family Full Below Cache */
     virtual std::shared_ptr<FullBelowCache>
     getFullBelowCache() = 0;

src/xrpld/shamap/NodeFamily.h

@@ -60,6 +60,9 @@ public:
         return j_;
     }
 
+    beast::xor_shift_engine&
+    prng() override;
+
     std::shared_ptr<FullBelowCache>
     getFullBelowCache() override
     {

src/xrpld/shamap/detail/NodeFamily.cpp

@@ -46,6 +46,12 @@ NodeFamily::NodeFamily(Application& app, CollectorManager& cm)
 {
 }
 
+beast::xor_shift_engine&
+NodeFamily::prng()
+{
+    return app_.getPrng();
+}
+
 void
 NodeFamily::sweep()
 {

src/xrpld/shamap/detail/SHAMapSync.cpp

@@ -235,7 +235,7 @@ SHAMap::gmn_ProcessNodes(MissingNodes& mn, MissingNodes::StackEntry& se)
                 // Switch to processing the child node
                 node = static_cast<SHAMapInnerNode*>(d);
                 nodeID = nodeID.getChildNodeID(branch);
-                firstChild = rand_int(255);
+                firstChild = rand_int(f_.prng(), 255);
                 currentChild = 0;
                 fullBelow = true;
             }
@@ -342,7 +342,7 @@ SHAMap::getMissingNodes(int max, SHAMapSyncFilter* filter)
     MissingNodes::StackEntry pos{
         static_cast<SHAMapInnerNode*>(root_.get()),
         SHAMapNodeID(),
-        rand_int(255),
+        rand_int(f_.prng(), 255),
         0,
         true};
     auto& node = std::get<0>(pos);
@@ -399,7 +399,7 @@ SHAMap::getMissingNodes(int max, SHAMapSyncFilter* filter)
                 for (auto const& [innerNode, nodeId] : mn.resumes_)
                     if (!innerNode->isFullBelow(mn.generation_))
                         mn.stack_.push(std::make_tuple(
-                            innerNode, nodeId, rand_int(255), 0, true));
+                            innerNode, nodeId, rand_int(f_.prng(), 255), 0, true));
 
                 mn.resumes_.clear();
             }