Fix empty service.instance.id by deferring node identity injection

The Telemetry object is constructed in ApplicationImp's member initializer
list where nodeIdentity_ is not yet available, resulting in an empty
service.instance.id resource attribute. Add setServiceInstanceId() virtual
method that Application::setup() calls after nodeIdentity_ is known but
before telemetry_->start() creates the OTel resource.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

include/xrpl/telemetry/Telemetry.h

@@ -108,6 +108,23 @@ public:
 
     virtual ~Telemetry() = default;
 
+    /** Update the service instance ID (OTel resource attribute
+        `service.instance.id`).
+
+        Must be called before start(). The node public key is not available
+        when Telemetry is constructed (during the ApplicationImp member
+        initializer list), so this setter allows Application::setup() to
+        inject the identity once nodeIdentity_ is known.
+
+        @param id  The node's base58-encoded public key or custom identifier.
+    */
+    virtual void
+    setServiceInstanceId(std::string const& id)
+    {
+        // Default no-op for NullTelemetry implementations.
+        (void)id;
+    }
+
     /** Initialize the tracing pipeline (exporter, processor, provider).
         Call after construction.
     */

src/libxrpl/telemetry/Telemetry.cpp

@@ -122,8 +122,11 @@ public:
 */
 class TelemetryImpl : public Telemetry
 {
-    /** Configuration from the [telemetry] config section. */
-    Setup const setup_;
+    /** Configuration from the [telemetry] config section.
+        Non-const so setServiceInstanceId() can update the instance ID
+        before start() creates the OTel resource.
+    */
+    Setup setup_;
 
     /** Journal used for log output during start/stop. */
     beast::Journal const journal_;
@@ -140,6 +143,12 @@ public:
     {
     }
 
+    void
+    setServiceInstanceId(std::string const& id) override
+    {
+        setup_.serviceInstanceId = id;
+    }
+
     void
     start() override
     {

src/xrpld/app/main/Application.cpp

@@ -263,7 +263,7 @@ public:
               telemetry::make_Telemetry(
                   telemetry::setup_Telemetry(
                       config_->section("telemetry"),
-                      "",  // nodePublicKey not yet available at this point
+                      "",  // Updated later via setServiceInstanceId()
                       BuildInfo::getVersionString()),
                   logs_->journal("Telemetry")))
 
@@ -1274,6 +1274,12 @@ ApplicationImp::setup(boost::program_options::variables_map const& cmdline)
 
     nodeIdentity_ = getNodeIdentity(*this, cmdline);
 
+    // Now that the node identity is known, inject it into the telemetry
+    // resource attributes.  The Telemetry object was constructed with an
+    // empty serviceInstanceId because nodeIdentity_ is not available in
+    // the ApplicationImp member initializer list.
+    telemetry_->setServiceInstanceId(toBase58(TokenType::NodePublic, nodeIdentity_->first));
+
     if (!cluster_->load(config().section(SECTION_CLUSTER_NODES)))
     {
         JLOG(m_journal.fatal()) << "Invalid entry in cluster configuration.";