fix(telemetry): start tracing before the first spans are emitted

telemetry_->start() ran at the end of ApplicationImp::start(), after
overlay_->start(). Spans are emitted well before that, during setup():
beginConsensus() runs the first consensus round there. SpanGuard drops a
span whenever the global Telemetry instance is not yet live, so that
round's spans were never recorded.

Move the start into setup(), behind a new startTelemetry() seam, right
after the node identity is known. getNodeIdentity() needs only the
cmdline, the config, or the wallet DB, and initRelationalDatabase()
has already created the latter -- the adjacent peerReservations_ load
proves it is usable -- so the identity block moves up with it.

The new position is bounded on both sides: after initRelationalDatabase()
because the identity needs the wallet DB and a DB failure aborts setup(),
and before beginConsensus() because that emits the first spans.

src/xrpld/app/main/Application.cpp

@@ -1141,6 +1141,22 @@ private:
     void
     startGenesisLedger();
 
+    /**
+     * Start the tracing pipeline.
+     *
+     * Called once from setup(), as soon as the node identity is known.
+     * Starting here rather than in start() means spans emitted during the
+     * rest of setup() are recorded: SpanGuard drops a span whenever the
+     * global Telemetry instance is not yet live, and the first consensus
+     * round runs inside setup().
+     *
+     * @pre nodeIdentity_ is populated, so setServiceInstanceId() has
+     * already supplied the service.instance.id resource attribute
+     * (the Telemetry resource is fixed once start() builds it).
+     */
+    void
+    startTelemetry();
+
     std::shared_ptr<Ledger>
     getLastFullLedger();
 
@@ -1227,6 +1243,27 @@ ApplicationImp::setup(boost::program_options::variables_map const& cmdline)
         return false;
     }
 
+    nodeIdentity_ = getNodeIdentity(*this, cmdline);
+
+    // Now that the node identity is known, inject it into the telemetry
+    // resource attributes — but only if the user didn't already set a
+    // custom service_instance_id in [telemetry].  The Telemetry object
+    // was constructed with an empty serviceInstanceId because
+    // nodeIdentity_ is not available in the member initializer list.
+    if (!config_->section("telemetry").exists("service_instance_id"))
+        telemetry_->setServiceInstanceId(toBase58(TokenType::NodePublic, nodeIdentity_->first));
+
+    // Start telemetry here, not in start(). Spans are emitted during the rest
+    // of setup() — the first consensus round in beginConsensus() below — and
+    // are dropped unless the global Telemetry instance is already live.
+    //
+    // The position is bounded on both sides:
+    //  - After initRelationalDatabase(): the wallet DB must exist for the node
+    //    identity above, and a DB failure aborts setup(), so starting earlier
+    //    would export a partial trace stream for a run that never comes up.
+    //  - Before beginConsensus(): that call emits the first consensus spans.
+    startTelemetry();
+
     if (validatorKeys_.keys)
         setMaxDisallowedLedger();
 
@@ -1314,16 +1351,6 @@ ApplicationImp::setup(boost::program_options::variables_map const& cmdline)
 
     orderBookDB_->setup(getLedgerMaster().getCurrentLedger());
 
-    nodeIdentity_ = getNodeIdentity(*this, cmdline);
-
-    // Now that the node identity is known, inject it into the telemetry
-    // resource attributes — but only if the user didn't already set a
-    // custom service_instance_id in [telemetry].  The Telemetry object
-    // was constructed with an empty serviceInstanceId because
-    // nodeIdentity_ is not available in the member initializer list.
-    if (!config_->section("telemetry").exists("service_instance_id"))
-        telemetry_->setServiceInstanceId(toBase58(TokenType::NodePublic, nodeIdentity_->first));
-
     if (!cluster_->load(config().section(Sections::kClusterNodes)))
     {
         JLOG(journal_.fatal()) << "Invalid entry in cluster configuration.";
@@ -1536,6 +1563,11 @@ ApplicationImp::start(bool withTimers)
 
     ledgerCleaner_->start();
     perfLog_->start();
+}
+
+void
+ApplicationImp::startTelemetry()
+{
     telemetry_->start();
 }