Merge branch 'pratik/otel-phase2-rpc-tracing' into pratik/otel-phase3-tx-tracing

Brings M1 (dropped-deterministic-id counter) + M2 (childSpan doc) forward.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

include/xrpl/telemetry/DeterministicIdGenerator.h

@@ -167,6 +167,22 @@ public:
     operator=(PendingTraceId&&) = delete;
 };
 
+/**
+ * Running count of deterministic trace_ids that were pinned by a
+ * PendingTraceId but never consumed by a forced-root span before the guard was
+ * destroyed. Bumped once per silent drop.
+ *
+ * ~PendingTraceId also asserts on this condition, but the assert is a no-op in
+ * release builds, so this monotonic counter is the only signal that a
+ * deterministic trace root was lost there. It is process-wide (summed across
+ * all threads) and intended for a future diagnostic metric or debugger
+ * inspection; reading it has no side effects.
+ *
+ * @return the total number of unconsumed deterministic trace_id drops so far.
+ */
+[[nodiscard]] std::uint64_t
+unconsumedDeterministicIdDrops() noexcept;
+
 }  // namespace xrpl::telemetry
 
 #endif  // XRPL_ENABLE_TELEMETRY

include/xrpl/telemetry/SpanGuard.h

@@ -329,10 +329,19 @@ public:
     // --- Child / linked span creation ----------------------------------
 
     /**
-     * Create a child span parented to the current thread's active
-     * context. This is meaningful when this guard's span is active on
-     * the thread (e.g. wrapped in a ScopedSpanGuard); otherwise the
-     * child inherits whatever context is currently on the stack.
+     * Create a child span parented to the CURRENT ambient context of this
+     * store, not to this guard's own span. It reads the active context via the
+     * runtime context store, so it is meaningful only when a scope is active on
+     * THIS store — a ScopedSpanGuard, a ScopedActivation, or this guard's span
+     * activated some other way. With coroutine-aware storage the ambient
+     * context is the correct parent in scoped and coroutine contexts (a
+     * coroutine keeps its store across a resume on another worker). When no
+     * scope is active the child inherits whatever context happens to be on the
+     * store, which may be unrelated.
+     *
+     * For explicit, store-independent parenting to a specific span (e.g.
+     * across stores or threads), capture spanContext() and use
+     * childSpan(name, ctx) instead.
      * @param name  Span name for the child.
      * @return A new guard, or null if this guard is inactive.
      */

src/libxrpl/telemetry/DeterministicIdGenerator.cpp

@@ -22,6 +22,7 @@
 #include <opentelemetry/trace/trace_id.h>
 
 #include <array>
+#include <atomic>
 #include <cstdint>
 #include <optional>
 
@@ -42,6 +43,14 @@ thread_local std::optional<std::array<std::uint8_t, 16>> gTlsPendingTraceId;
  */
 thread_local bool gTlsPendingConsumed = false;
 
+/**
+ * Process-wide count of deterministic trace_ids dropped without being consumed.
+ * Bumped in ~PendingTraceId when the pending id was never taken by a root span.
+ * Atomic because it is summed across all threads; relaxed ordering is enough
+ * for a diagnostic tally. Exposed via unconsumedDeterministicIdDrops().
+ */
+std::atomic<std::uint64_t> gUnconsumedDeterministicIdDrops{0};
+
 }  // namespace
 
 DeterministicIdGenerator::DeterministicIdGenerator()
@@ -84,10 +93,23 @@ PendingTraceId::~PendingTraceId() noexcept
     XRPL_ASSERT(
         gTlsPendingConsumed,
         "xrpl::telemetry::PendingTraceId : deterministic trace_id was not consumed");
+    if (!gTlsPendingConsumed)
+    {
+        // The assert above is stripped in release, so bump a counter too: a
+        // dropped deterministic trace root stays observable via
+        // unconsumedDeterministicIdDrops(). Relaxed: this is a diagnostic tally.
+        gUnconsumedDeterministicIdDrops.fetch_add(1, std::memory_order_relaxed);
+    }
     gTlsPendingTraceId.reset();  // never leak, even in release
     gTlsPendingConsumed = false;
 }
 
+std::uint64_t
+unconsumedDeterministicIdDrops() noexcept
+{
+    return gUnconsumedDeterministicIdDrops.load(std::memory_order_relaxed);
+}
+
 }  // namespace xrpl::telemetry
 
 #endif  // XRPL_ENABLE_TELEMETRY