fix(telemetry): CI Werror — registry .get() and unused fields

Two build failures surfaced by CI on the Phase 9 branch:

1. NetworkOPsImp stores the ServiceRegistry as
   std::reference_wrapper<ServiceRegistry> registry_, so calls must go
   through registry_.get().<method>(). The MetricsRegistry hooks added
   in setMode() and recvValidation() dereferenced the wrapper directly,
   which compiles against a pre-existing accessor on the wrapper type
   on some toolchains but fails on clang 16/17/20 and gcc 13/15 with
   "no member named 'getMetricsRegistry' in
   std::reference_wrapper<xrpl::ServiceRegistry>".

2. MetricsRegistry::app_ and MetricsRegistry::journal_ are only used
   inside XRPL_ENABLE_TELEMETRY-guarded code paths (gauge callbacks
   and JLOG). When telemetry is disabled, clang's
   -Werror=-Wunused-private-field tripped. Move the two fields under
   the same #ifdef and guard the constructor initialisers with
   [[maybe_unused]] so the no-op build continues to compile cleanly.

src/xrpld/app/misc/NetworkOPs.cpp

@@ -2536,7 +2536,7 @@ NetworkOPsImp::setMode(OperatingMode om)
     accounting_.mode(om);
 
     // Record state change for OTel dashboard parity counter.
-    if (auto* mr = registry_.getMetricsRegistry())
+    if (auto* mr = registry_.get().getMetricsRegistry())
         mr->incrementStateChanges();
 
     JLOG(m_journal.info()) << "STATE->" << strOperatingMode();
@@ -2547,7 +2547,7 @@ bool
 NetworkOPsImp::recvValidation(std::shared_ptr<STValidation> const& val, std::string const& source)
 {
     JLOG(m_journal.trace()) << "recvValidation " << val->getLedgerHash() << " from " << source;
-    if (auto* mr = registry_.getMetricsRegistry())
+    if (auto* mr = registry_.get().getMetricsRegistry())
         mr->incrementValidationsChecked();
 
     std::unique_lock lock(validationsMutex_);

src/xrpld/telemetry/MetricsRegistry.cpp

@@ -65,8 +65,15 @@ namespace resource = opentelemetry::sdk::resource;
 namespace xrpl {
 namespace telemetry {
 
-MetricsRegistry::MetricsRegistry(bool enabled, ServiceRegistry& app, beast::Journal journal)
-    : enabled_(enabled), app_(app), journal_(journal)
+MetricsRegistry::MetricsRegistry(
+    [[maybe_unused]] bool enabled,
+    [[maybe_unused]] ServiceRegistry& app,
+    [[maybe_unused]] beast::Journal journal)
+    : enabled_(enabled)
+#ifdef XRPL_ENABLE_TELEMETRY
+    , app_(app)
+    , journal_(journal)
+#endif
 {
 }
 

src/xrpld/telemetry/MetricsRegistry.h

@@ -340,12 +340,6 @@ private:
     /// Master enable flag; when false all methods are no-ops.
     bool const enabled_;
 
-    /// Reference to Application services for gauge callbacks.
-    ServiceRegistry& app_;
-
-    /// Journal for logging.
-    beast::Journal const journal_;
-
     /// Tracks validation agreement between this node and the network.
     /// Lives outside the XRPL_ENABLE_TELEMETRY guard because it is
     /// always safe to record events; the gauge callback simply won't
@@ -353,6 +347,13 @@ private:
     ValidationTracker validationTracker_;
 
 #ifdef XRPL_ENABLE_TELEMETRY
+    /// Reference to Application services for gauge callbacks.
+    /// Only needed when OTel is compiled in, since observable gauge
+    /// callbacks live entirely inside the XRPL_ENABLE_TELEMETRY guard.
+    ServiceRegistry& app_;
+
+    /// Journal for logging.
+    beast::Journal const journal_;
     /// The SDK MeterProvider that owns the export pipeline.
     std::shared_ptr<opentelemetry::sdk::metrics::MeterProvider> provider_;