docs(telemetry): InboundLedger acquireSpan_ is thread-free, not detached

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

src/xrpld/app/ledger/InboundLedger.h

@@ -201,10 +201,9 @@ private:
      * with the outcome (complete/failed), timeout count, and peer count.
      * Gives operators visibility into back-fill / fork-recovery cost, which
      * previously emitted no span or metric.
-     * Stored detached: emplaced by the acquiring thread, reset on a
-     * JtLedgerData worker. detached() strips the thread-local Scope so the
-     * guard can be destroyed on the worker without corrupting the origin
-     * thread's context stack.
+     * Thread-free: emplaced by the acquiring thread, reset on a JtLedgerData
+     * worker. A SpanGuard owns no thread-local Scope, so it can be destroyed
+     * on the worker without corrupting the origin thread's context stack.
      */
     std::optional<telemetry::SpanGuard> acquireSpan_;
 };